JIT: Stack allocate non-escaping strings#129202

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EgorBo wants to merge 8 commits into from
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JIT: Stack allocate non-escaping strings #129202

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3198d9e
JIT: Stack allocate non-escaping strings
EgorBo Jun 10, 2026
ef02bad
JIT: Merge string stack-alloc into the array path
EgorBo Jun 10, 2026
622f7fa
Merge branch 'main' into egorbo/jit-stackalloc-strings
EgorBo Jun 10, 2026
0858d0a
Merge branch 'main' into egorbo/jit-stackalloc-strings
EgorBo Jun 22, 2026
506834d
Merge branch 'main' into egorbo/jit-stackalloc-strings
EgorBo Jun 26, 2026
f6bfc0b
Merge branch 'main' into egorbo/jit-stackalloc-strings
EgorBo Jul 6, 2026
79c4877
JIT: Add FileCheck tests for stack-allocated strings
EgorBo Jul 6, 2026
0f922cb
Potential fix for pull request finding
EgorBo Jul 6, 2026
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1 change: 1 addition & 0 deletions src/coreclr/jit/compiler.h
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Original file line numberDiff line numberDiff line change
Expand Up@@ -8008,6 +8008,7 @@ class Compiler
#define OMF_HAS_STACK_ARRAY 0x00100000 // Method contains stack allocated arrays
#define OMF_HAS_BOUNDS_CHECKS 0x00200000 // Method contains bounds checks
#define OMF_HAS_EARLY_QMARKS 0x00400000 // Method contains early expandable QMARKs
#define OMF_HAS_FASTSTRINGALLOC 0x00800000 // Method contains String.FastAllocateString calls

// clang-format on

Expand Down
68 changes: 40 additions & 28 deletions src/coreclr/jit/helperexpansion.cpp
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Original file line numberDiff line numberDiff line change
Expand Up@@ -2848,30 +2848,42 @@ PhaseStatus Compiler::fgExpandStackArrayAllocations()
//
bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt, GenTreeCall* call)
{
if (!call->IsHelperCall())
{
return false;
}

const CorInfoHelpFunc helper = call->GetHelperNum();
int lengthArgIndex = -1;
int typeArgIndex = -1;
int lengthArgIndex = -1;
int typeArgIndex = -1;
unsigned lengthOffset = 0;

switch (helper)
if (call->IsHelperCall())
{
case CORINFO_HELP_NEWARR_1_DIRECT:
case CORINFO_HELP_NEWARR_1_VC:
case CORINFO_HELP_NEWARR_1_PTR:
case CORINFO_HELP_NEWARR_1_ALIGN8:
lengthArgIndex = 1;
typeArgIndex = 0;
break;
switch (call->GetHelperNum())
{
case CORINFO_HELP_NEWARR_1_DIRECT:
case CORINFO_HELP_NEWARR_1_VC:
case CORINFO_HELP_NEWARR_1_PTR:
case CORINFO_HELP_NEWARR_1_ALIGN8:
lengthArgIndex = 1;
typeArgIndex = 0;
lengthOffset = OFFSETOF__CORINFO_Array__length;
break;

default:
return false;
default:
return false;
}
}
else if (call->IsSpecialIntrinsic(this, NI_System_String_FastAllocateString))
{
// Strings are modelled as FastAllocateString(pMT, length) and reuse the array
// stack allocation path; only the length field offset differs.
//
lengthArgIndex = 1;
typeArgIndex = 0;
lengthOffset = OFFSETOF__CORINFO_String__stringLen;
}
else
{
return false;
}

// If this is a local array, the new helper will have an arg for the array's address
// If this is a local array or string, the call will have an arg for the object's address
//
CallArg* const stackLocalAddressArg = call->gtArgs.FindWellKnownArg(WellKnownArg::StackArrayLocal);

Expand All@@ -2880,7 +2892,7 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,
return false;
}

JITDUMP("Expanding new array helper for stack allocated array at [%06d] in " FMT_BB ":\n", dspTreeID(call),
JITDUMP("Expanding new array/string helper for stack allocated object at [%06d] in " FMT_BB ":\n", dspTreeID(call),
block->bbNum);
DISPTREE(call);
JITDUMP("\n");
Expand All@@ -2900,22 +2912,22 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,

GenTree* const stackLocalAddress = stackLocalAddressArg->GetNode();

// Initialize the array method table pointer.
// Initialize the method table pointer.
//
GenTree* const mt = call->gtArgs.GetArgByIndex(typeArgIndex)->GetNode();
GenTree* const mtStore = gtNewStoreValueNode(TYP_I_IMPL, stackLocalAddress, mt);
Statement* const mtStmt = fgNewStmtFromTree(mtStore);

fgInsertStmtBefore(block, stmt, mtStmt);

// Initialize the array length.
// Initialize the array/string length.
//
GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
GenTree* const lengthAddress = gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress),
gtNewIconNode(OFFSETOF__CORINFO_Array__length, TYP_I_IMPL));
GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
Statement* const lenStmt = fgNewStmtFromTree(lengthStore);
GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
GenTree* const lengthAddress =
gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress), gtNewIconNode(lengthOffset, TYP_I_IMPL));
GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
Statement* const lenStmt = fgNewStmtFromTree(lengthStore);

fgInsertStmtBefore(block, stmt, lenStmt);

Expand Down
6 changes: 6 additions & 0 deletions src/coreclr/jit/importercalls.cpp
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Open in desktop
Original file line numberDiff line numberDiff line change
Expand Up@@ -4148,7 +4148,13 @@ GenTree* Compiler::impIntrinsic(CORINFO_CLASS_HANDLE clsHnd,
}

case NI_System_ArgumentNullException_ThrowIfNull:
isSpecial = true;
break;

case NI_System_String_FastAllocateString:
// Flag the method so the object allocator runs its escape analysis and can
// stack allocate non-escaping, constant-length strings.
optMethodFlags |= OMF_HAS_FASTSTRINGALLOC;
isSpecial = true;
break;

Expand Down
1 change: 1 addition & 0 deletions src/coreclr/jit/jitconfigvalues.h
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Open in desktop
Original file line numberDiff line numberDiff line change
Expand Up@@ -713,6 +713,7 @@ RELEASE_CONFIG_INTEGER(JitObjectStackAllocationBoxedValueClass, "JitObjectStackA
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationConditionalEscape, "JitObjectStackAllocationConditionalEscape", 1)
CONFIG_STRING(JitObjectStackAllocationConditionalEscapeRange, "JitObjectStackAllocationConditionalEscapeRange")
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationArray, "JitObjectStackAllocationArray", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationString, "JitObjectStackAllocationString", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationSize, "JitObjectStackAllocationSize", 528)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationTrackFields, "JitObjectStackAllocationTrackFields", 1)
CONFIG_STRING(JitObjectStackAllocationTrackFieldsRange, "JitObjectStackAllocationTrackFieldsRange")
Expand Down
2 changes: 2 additions & 0 deletions src/coreclr/jit/jitmetadatalist.h
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Original file line numberDiff line numberDiff line change
Expand Up@@ -89,6 +89,8 @@ JITMETADATAMETRIC(NewBoxedValueClassHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedBoxedValueClasses, int, 0)
JITMETADATAMETRIC(NewArrayHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedArrays, int, 0)
JITMETADATAMETRIC(NewStringAllocations, int, 0)
JITMETADATAMETRIC(StackAllocatedStrings, int, 0)
JITMETADATAMETRIC(LocalAssertionCount, int, 0)
JITMETADATAMETRIC(LocalAssertionOverflow, int, 0)
JITMETADATAMETRIC(MorphTrackedLocals, int, 0)
Expand Down
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, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
 blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

Skip to content
JIT: Stack allocate non-escaping strings#129202

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 Closed

EgorBo
wants to merge
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commits into

from

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JIT: Stack allocate non-escaping strings
#129202
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3198d9e

JIT: Stack allocate non-escaping strings


EgorBo Jun 10, 2026
ef02bad

JIT: Merge string stack-alloc into the array path


EgorBo Jun 10, 2026
622f7fa

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 10, 2026
0858d0a

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 22, 2026
506834d

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 26, 2026
f6bfc0b

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jul 6, 2026
79c4877

JIT: Add FileCheck tests for stack-allocated strings


EgorBo Jul 6, 2026
0f922cb

Potential fix for pull request finding


EgorBo Jul 6, 2026

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1 change: 1 addition & 0 deletions
src/coreclr/jit/compiler.h

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -8008,6 +8008,7 @@ class Compiler
#define OMF_HAS_STACK_ARRAY 0x00100000 // Method contains stack allocated arrays
#define OMF_HAS_BOUNDS_CHECKS 0x00200000 // Method contains bounds checks
#define OMF_HAS_EARLY_QMARKS 0x00400000 // Method contains early expandable QMARKs
#define OMF_HAS_FASTSTRINGALLOC 0x00800000 // Method contains String.FastAllocateString calls

 // clang-format on

Expand Down

68 changes: 40 additions & 28 deletions
src/coreclr/jit/helperexpansion.cpp

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2848,30 +2848,42 @@ PhaseStatus Compiler::fgExpandStackArrayAllocations()
//
bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt, GenTreeCall* call)
{
 if (!call->IsHelperCall())
 {
 return false;
 }

 const CorInfoHelpFunc helper = call->GetHelperNum();
 int lengthArgIndex = -1;
 int typeArgIndex = -1;
 int lengthArgIndex = -1;
 int typeArgIndex = -1;
 unsigned lengthOffset = 0;

switch (helper)
if (call->IsHelperCall())
 {
 case CORINFO_HELP_NEWARR_1_DIRECT:
 case CORINFO_HELP_NEWARR_1_VC:
 case CORINFO_HELP_NEWARR_1_PTR:
 case CORINFO_HELP_NEWARR_1_ALIGN8:
 lengthArgIndex = 1;
 typeArgIndex = 0;
 break;
 switch (call->GetHelperNum())
 {
 case CORINFO_HELP_NEWARR_1_DIRECT:
 case CORINFO_HELP_NEWARR_1_VC:
 case CORINFO_HELP_NEWARR_1_PTR:
 case CORINFO_HELP_NEWARR_1_ALIGN8:
 lengthArgIndex = 1;
 typeArgIndex = 0;
 lengthOffset = OFFSETOF__CORINFO_Array__length;
 break;

 default:
 return false;
 default:
 return false;
 }
 }
 else if (call->IsSpecialIntrinsic(this, NI_System_String_FastAllocateString))
 {
 // Strings are modelled as FastAllocateString(pMT, length) and reuse the array
 // stack allocation path; only the length field offset differs.
 //
 lengthArgIndex = 1;
 typeArgIndex = 0;
 lengthOffset = OFFSETOF__CORINFO_String__stringLen;
 }
 else
 {
 return false;
 }

 // If this is a local array, the new helper will have an arg for the array's address
 // If this is a local array or string, the call will have an arg for the object's address
 //
 CallArg* const stackLocalAddressArg = call->gtArgs.FindWellKnownArg(WellKnownArg::StackArrayLocal);

Expand All@@ -2880,7 +2892,7 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,
 return false;
 }

 JITDUMP("Expanding new array helper for stack allocated array at [%06d] in " FMT_BB ":\n", dspTreeID(call),
 JITDUMP("Expanding new array/string helper for stack allocated object at [%06d] in " FMT_BB ":\n", dspTreeID(call),
 block->bbNum);
 DISPTREE(call);
 JITDUMP("\n");
Expand All@@ -2900,22 +2912,22 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,

 GenTree* const stackLocalAddress = stackLocalAddressArg->GetNode();

 // Initialize the array method table pointer.
 // Initialize the method table pointer.
 //
 GenTree* const mt = call->gtArgs.GetArgByIndex(typeArgIndex)->GetNode();
 GenTree* const mtStore = gtNewStoreValueNode(TYP_I_IMPL, stackLocalAddress, mt);
 Statement* const mtStmt = fgNewStmtFromTree(mtStore);

 fgInsertStmtBefore(block, stmt, mtStmt);

 // Initialize the array length.
 // Initialize the array/string length.
 //
 GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
 GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
 GenTree* const lengthAddress = gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress),
gtNewIconNode(OFFSETOF__CORINFO_Array__length, TYP_I_IMPL));
 GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
 Statement* const lenStmt = fgNewStmtFromTree(lengthStore);
 GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
 GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
 GenTree* const lengthAddress =
gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress), gtNewIconNode(lengthOffset, TYP_I_IMPL));
 GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
 Statement* const lenStmt = fgNewStmtFromTree(lengthStore);

 fgInsertStmtBefore(block, stmt, lenStmt);

Expand Down

6 changes: 6 additions & 0 deletions
src/coreclr/jit/importercalls.cpp

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Original file line numberDiff line numberDiff line change
Expand Up@@ -4148,7 +4148,13 @@ GenTree* Compiler::impIntrinsic(CORINFO_CLASS_HANDLE clsHnd,
 }

 case NI_System_ArgumentNullException_ThrowIfNull:
 isSpecial = true;
 break;

 case NI_System_String_FastAllocateString:
 // Flag the method so the object allocator runs its escape analysis and can
 // stack allocate non-escaping, constant-length strings.
 optMethodFlags |= OMF_HAS_FASTSTRINGALLOC;
 isSpecial = true;
 break;

Expand Down

1 change: 1 addition & 0 deletions
src/coreclr/jit/jitconfigvalues.h

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Original file line numberDiff line numberDiff line change
Expand Up@@ -713,6 +713,7 @@ RELEASE_CONFIG_INTEGER(JitObjectStackAllocationBoxedValueClass, "JitObjectStackA
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationConditionalEscape, "JitObjectStackAllocationConditionalEscape", 1)
CONFIG_STRING(JitObjectStackAllocationConditionalEscapeRange, "JitObjectStackAllocationConditionalEscapeRange")
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationArray, "JitObjectStackAllocationArray", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationString, "JitObjectStackAllocationString", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationSize, "JitObjectStackAllocationSize", 528)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationTrackFields, "JitObjectStackAllocationTrackFields", 1)
CONFIG_STRING(JitObjectStackAllocationTrackFieldsRange, "JitObjectStackAllocationTrackFieldsRange")
Expand Down

2 changes: 2 additions & 0 deletions
src/coreclr/jit/jitmetadatalist.h

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Original file line numberDiff line numberDiff line change
Expand Up@@ -89,6 +89,8 @@ JITMETADATAMETRIC(NewBoxedValueClassHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedBoxedValueClasses, int, 0)
JITMETADATAMETRIC(NewArrayHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedArrays, int, 0)
JITMETADATAMETRIC(NewStringAllocations, int, 0)
JITMETADATAMETRIC(StackAllocatedStrings, int, 0)
JITMETADATAMETRIC(LocalAssertionCount, int, 0)
JITMETADATAMETRIC(LocalAssertionOverflow, int, 0)
JITMETADATAMETRIC(MorphTrackedLocals, int, 0)
Expand Down
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
JIT: Stack allocate non-escaping strings#129202

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Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

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 Closed

EgorBo
wants to merge
8
commits into

from

 Closed


JIT: Stack allocate non-escaping strings
#129202
Show file tree
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Commits

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8 commits


Select commit
Hold shift + click to select a range
3198d9e

JIT: Stack allocate non-escaping strings


EgorBo Jun 10, 2026
ef02bad

JIT: Merge string stack-alloc into the array path


EgorBo Jun 10, 2026
622f7fa

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 10, 2026
0858d0a

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 22, 2026
506834d

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 26, 2026
f6bfc0b

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jul 6, 2026
79c4877

JIT: Add FileCheck tests for stack-allocated strings


EgorBo Jul 6, 2026
0f922cb

Potential fix for pull request finding


EgorBo Jul 6, 2026

File filter

Filter by extension
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1 change: 1 addition & 0 deletions
src/coreclr/jit/compiler.h

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -8008,6 +8008,7 @@ class Compiler
#define OMF_HAS_STACK_ARRAY 0x00100000 // Method contains stack allocated arrays
#define OMF_HAS_BOUNDS_CHECKS 0x00200000 // Method contains bounds checks
#define OMF_HAS_EARLY_QMARKS 0x00400000 // Method contains early expandable QMARKs
#define OMF_HAS_FASTSTRINGALLOC 0x00800000 // Method contains String.FastAllocateString calls

 // clang-format on

Expand Down

68 changes: 40 additions & 28 deletions
src/coreclr/jit/helperexpansion.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2848,30 +2848,42 @@ PhaseStatus Compiler::fgExpandStackArrayAllocations()
//
bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt, GenTreeCall* call)
{
 if (!call->IsHelperCall())
 {
 return false;
 }

 const CorInfoHelpFunc helper = call->GetHelperNum();
 int lengthArgIndex = -1;
 int typeArgIndex = -1;
 int lengthArgIndex = -1;
 int typeArgIndex = -1;
 unsigned lengthOffset = 0;

switch (helper)
if (call->IsHelperCall())
 {
 case CORINFO_HELP_NEWARR_1_DIRECT:
 case CORINFO_HELP_NEWARR_1_VC:
 case CORINFO_HELP_NEWARR_1_PTR:
 case CORINFO_HELP_NEWARR_1_ALIGN8:
 lengthArgIndex = 1;
 typeArgIndex = 0;
 break;
 switch (call->GetHelperNum())
 {
 case CORINFO_HELP_NEWARR_1_DIRECT:
 case CORINFO_HELP_NEWARR_1_VC:
 case CORINFO_HELP_NEWARR_1_PTR:
 case CORINFO_HELP_NEWARR_1_ALIGN8:
 lengthArgIndex = 1;
 typeArgIndex = 0;
 lengthOffset = OFFSETOF__CORINFO_Array__length;
 break;

 default:
 return false;
 default:
 return false;
 }
 }
 else if (call->IsSpecialIntrinsic(this, NI_System_String_FastAllocateString))
 {
 // Strings are modelled as FastAllocateString(pMT, length) and reuse the array
 // stack allocation path; only the length field offset differs.
 //
 lengthArgIndex = 1;
 typeArgIndex = 0;
 lengthOffset = OFFSETOF__CORINFO_String__stringLen;
 }
 else
 {
 return false;
 }

 // If this is a local array, the new helper will have an arg for the array's address
 // If this is a local array or string, the call will have an arg for the object's address
 //
 CallArg* const stackLocalAddressArg = call->gtArgs.FindWellKnownArg(WellKnownArg::StackArrayLocal);

Expand All@@ -2880,7 +2892,7 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,
 return false;
 }

 JITDUMP("Expanding new array helper for stack allocated array at [%06d] in " FMT_BB ":\n", dspTreeID(call),
 JITDUMP("Expanding new array/string helper for stack allocated object at [%06d] in " FMT_BB ":\n", dspTreeID(call),
 block->bbNum);
 DISPTREE(call);
 JITDUMP("\n");
Expand All@@ -2900,22 +2912,22 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,

 GenTree* const stackLocalAddress = stackLocalAddressArg->GetNode();

 // Initialize the array method table pointer.
 // Initialize the method table pointer.
 //
 GenTree* const mt = call->gtArgs.GetArgByIndex(typeArgIndex)->GetNode();
 GenTree* const mtStore = gtNewStoreValueNode(TYP_I_IMPL, stackLocalAddress, mt);
 Statement* const mtStmt = fgNewStmtFromTree(mtStore);

 fgInsertStmtBefore(block, stmt, mtStmt);

 // Initialize the array length.
 // Initialize the array/string length.
 //
 GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
 GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
 GenTree* const lengthAddress = gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress),
gtNewIconNode(OFFSETOF__CORINFO_Array__length, TYP_I_IMPL));
 GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
 Statement* const lenStmt = fgNewStmtFromTree(lengthStore);
 GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
 GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
 GenTree* const lengthAddress =
gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress), gtNewIconNode(lengthOffset, TYP_I_IMPL));
 GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
 Statement* const lenStmt = fgNewStmtFromTree(lengthStore);

 fgInsertStmtBefore(block, stmt, lenStmt);

Expand Down

6 changes: 6 additions & 0 deletions
src/coreclr/jit/importercalls.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -4148,7 +4148,13 @@ GenTree* Compiler::impIntrinsic(CORINFO_CLASS_HANDLE clsHnd,
 }

 case NI_System_ArgumentNullException_ThrowIfNull:
 isSpecial = true;
 break;

 case NI_System_String_FastAllocateString:
 // Flag the method so the object allocator runs its escape analysis and can
 // stack allocate non-escaping, constant-length strings.
 optMethodFlags |= OMF_HAS_FASTSTRINGALLOC;
 isSpecial = true;
 break;

Expand Down

1 change: 1 addition & 0 deletions
src/coreclr/jit/jitconfigvalues.h

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -713,6 +713,7 @@ RELEASE_CONFIG_INTEGER(JitObjectStackAllocationBoxedValueClass, "JitObjectStackA
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationConditionalEscape, "JitObjectStackAllocationConditionalEscape", 1)
CONFIG_STRING(JitObjectStackAllocationConditionalEscapeRange, "JitObjectStackAllocationConditionalEscapeRange")
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationArray, "JitObjectStackAllocationArray", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationString, "JitObjectStackAllocationString", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationSize, "JitObjectStackAllocationSize", 528)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationTrackFields, "JitObjectStackAllocationTrackFields", 1)
CONFIG_STRING(JitObjectStackAllocationTrackFieldsRange, "JitObjectStackAllocationTrackFieldsRange")
Expand Down

2 changes: 2 additions & 0 deletions
src/coreclr/jit/jitmetadatalist.h

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -89,6 +89,8 @@ JITMETADATAMETRIC(NewBoxedValueClassHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedBoxedValueClasses, int, 0)
JITMETADATAMETRIC(NewArrayHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedArrays, int, 0)
JITMETADATAMETRIC(NewStringAllocations, int, 0)
JITMETADATAMETRIC(StackAllocatedStrings, int, 0)
JITMETADATAMETRIC(LocalAssertionCount, int, 0)
JITMETADATAMETRIC(LocalAssertionOverflow, int, 0)
JITMETADATAMETRIC(MorphTrackedLocals, int, 0)
Expand Down
Loading
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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JIT: Stack allocate non-escaping strings#129202

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EgorBo
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from

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JIT: Stack allocate non-escaping strings
#129202
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3198d9e

JIT: Stack allocate non-escaping strings


EgorBo Jun 10, 2026
ef02bad

JIT: Merge string stack-alloc into the array path


EgorBo Jun 10, 2026
622f7fa

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 10, 2026
0858d0a

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 22, 2026
506834d

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 26, 2026
f6bfc0b

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jul 6, 2026
79c4877

JIT: Add FileCheck tests for stack-allocated strings


EgorBo Jul 6, 2026
0f922cb

Potential fix for pull request finding


EgorBo Jul 6, 2026

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1 change: 1 addition & 0 deletions
src/coreclr/jit/compiler.h

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -8008,6 +8008,7 @@ class Compiler
#define OMF_HAS_STACK_ARRAY 0x00100000 // Method contains stack allocated arrays
#define OMF_HAS_BOUNDS_CHECKS 0x00200000 // Method contains bounds checks
#define OMF_HAS_EARLY_QMARKS 0x00400000 // Method contains early expandable QMARKs
#define OMF_HAS_FASTSTRINGALLOC 0x00800000 // Method contains String.FastAllocateString calls

 // clang-format on

Expand Down

68 changes: 40 additions & 28 deletions
src/coreclr/jit/helperexpansion.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2848,30 +2848,42 @@ PhaseStatus Compiler::fgExpandStackArrayAllocations()
//
bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt, GenTreeCall* call)
{
 if (!call->IsHelperCall())
 {
 return false;
 }

 const CorInfoHelpFunc helper = call->GetHelperNum();
 int lengthArgIndex = -1;
 int typeArgIndex = -1;
 int lengthArgIndex = -1;
 int typeArgIndex = -1;
 unsigned lengthOffset = 0;

switch (helper)
if (call->IsHelperCall())
 {
 case CORINFO_HELP_NEWARR_1_DIRECT:
 case CORINFO_HELP_NEWARR_1_VC:
 case CORINFO_HELP_NEWARR_1_PTR:
 case CORINFO_HELP_NEWARR_1_ALIGN8:
 lengthArgIndex = 1;
 typeArgIndex = 0;
 break;
 switch (call->GetHelperNum())
 {
 case CORINFO_HELP_NEWARR_1_DIRECT:
 case CORINFO_HELP_NEWARR_1_VC:
 case CORINFO_HELP_NEWARR_1_PTR:
 case CORINFO_HELP_NEWARR_1_ALIGN8:
 lengthArgIndex = 1;
 typeArgIndex = 0;
 lengthOffset = OFFSETOF__CORINFO_Array__length;
 break;

 default:
 return false;
 default:
 return false;
 }
 }
 else if (call->IsSpecialIntrinsic(this, NI_System_String_FastAllocateString))
 {
 // Strings are modelled as FastAllocateString(pMT, length) and reuse the array
 // stack allocation path; only the length field offset differs.
 //
 lengthArgIndex = 1;
 typeArgIndex = 0;
 lengthOffset = OFFSETOF__CORINFO_String__stringLen;
 }
 else
 {
 return false;
 }

 // If this is a local array, the new helper will have an arg for the array's address
 // If this is a local array or string, the call will have an arg for the object's address
 //
 CallArg* const stackLocalAddressArg = call->gtArgs.FindWellKnownArg(WellKnownArg::StackArrayLocal);

Expand All@@ -2880,7 +2892,7 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,
 return false;
 }

 JITDUMP("Expanding new array helper for stack allocated array at [%06d] in " FMT_BB ":\n", dspTreeID(call),
 JITDUMP("Expanding new array/string helper for stack allocated object at [%06d] in " FMT_BB ":\n", dspTreeID(call),
 block->bbNum);
 DISPTREE(call);
 JITDUMP("\n");
Expand All@@ -2900,22 +2912,22 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,

 GenTree* const stackLocalAddress = stackLocalAddressArg->GetNode();

 // Initialize the array method table pointer.
 // Initialize the method table pointer.
 //
 GenTree* const mt = call->gtArgs.GetArgByIndex(typeArgIndex)->GetNode();
 GenTree* const mtStore = gtNewStoreValueNode(TYP_I_IMPL, stackLocalAddress, mt);
 Statement* const mtStmt = fgNewStmtFromTree(mtStore);

 fgInsertStmtBefore(block, stmt, mtStmt);

 // Initialize the array length.
 // Initialize the array/string length.
 //
 GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
 GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
 GenTree* const lengthAddress = gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress),
gtNewIconNode(OFFSETOF__CORINFO_Array__length, TYP_I_IMPL));
 GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
 Statement* const lenStmt = fgNewStmtFromTree(lengthStore);
 GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
 GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
 GenTree* const lengthAddress =
gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress), gtNewIconNode(lengthOffset, TYP_I_IMPL));
 GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
 Statement* const lenStmt = fgNewStmtFromTree(lengthStore);

 fgInsertStmtBefore(block, stmt, lenStmt);

Expand Down

6 changes: 6 additions & 0 deletions
src/coreclr/jit/importercalls.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -4148,7 +4148,13 @@ GenTree* Compiler::impIntrinsic(CORINFO_CLASS_HANDLE clsHnd,
 }

 case NI_System_ArgumentNullException_ThrowIfNull:
 isSpecial = true;
 break;

 case NI_System_String_FastAllocateString:
 // Flag the method so the object allocator runs its escape analysis and can
 // stack allocate non-escaping, constant-length strings.
 optMethodFlags |= OMF_HAS_FASTSTRINGALLOC;
 isSpecial = true;
 break;

Expand Down

1 change: 1 addition & 0 deletions
src/coreclr/jit/jitconfigvalues.h

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -713,6 +713,7 @@ RELEASE_CONFIG_INTEGER(JitObjectStackAllocationBoxedValueClass, "JitObjectStackA
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationConditionalEscape, "JitObjectStackAllocationConditionalEscape", 1)
CONFIG_STRING(JitObjectStackAllocationConditionalEscapeRange, "JitObjectStackAllocationConditionalEscapeRange")
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationArray, "JitObjectStackAllocationArray", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationString, "JitObjectStackAllocationString", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationSize, "JitObjectStackAllocationSize", 528)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationTrackFields, "JitObjectStackAllocationTrackFields", 1)
CONFIG_STRING(JitObjectStackAllocationTrackFieldsRange, "JitObjectStackAllocationTrackFieldsRange")
Expand Down

2 changes: 2 additions & 0 deletions
src/coreclr/jit/jitmetadatalist.h

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -89,6 +89,8 @@ JITMETADATAMETRIC(NewBoxedValueClassHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedBoxedValueClasses, int, 0)
JITMETADATAMETRIC(NewArrayHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedArrays, int, 0)
JITMETADATAMETRIC(NewStringAllocations, int, 0)
JITMETADATAMETRIC(StackAllocatedStrings, int, 0)
JITMETADATAMETRIC(LocalAssertionCount, int, 0)
JITMETADATAMETRIC(LocalAssertionOverflow, int, 0)
JITMETADATAMETRIC(MorphTrackedLocals, int, 0)
Expand Down
Loading
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

Skip to content
JIT: Stack allocate non-escaping strings#129202

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

 Sign up for GitHub

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privacy statement. We’ll occasionally send you account related emails.

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to your account

 Closed

EgorBo
wants to merge
8
commits into

from

 Closed


JIT: Stack allocate non-escaping strings
#129202
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3198d9e

JIT: Stack allocate non-escaping strings


EgorBo Jun 10, 2026
ef02bad

JIT: Merge string stack-alloc into the array path


EgorBo Jun 10, 2026
622f7fa

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 10, 2026
0858d0a

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 22, 2026
506834d

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 26, 2026
f6bfc0b

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jul 6, 2026
79c4877

JIT: Add FileCheck tests for stack-allocated strings


EgorBo Jul 6, 2026
0f922cb

Potential fix for pull request finding


EgorBo Jul 6, 2026

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1 change: 1 addition & 0 deletions
src/coreclr/jit/compiler.h

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -8008,6 +8008,7 @@ class Compiler
#define OMF_HAS_STACK_ARRAY 0x00100000 // Method contains stack allocated arrays
#define OMF_HAS_BOUNDS_CHECKS 0x00200000 // Method contains bounds checks
#define OMF_HAS_EARLY_QMARKS 0x00400000 // Method contains early expandable QMARKs
#define OMF_HAS_FASTSTRINGALLOC 0x00800000 // Method contains String.FastAllocateString calls

 // clang-format on

Expand Down

68 changes: 40 additions & 28 deletions
src/coreclr/jit/helperexpansion.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2848,30 +2848,42 @@ PhaseStatus Compiler::fgExpandStackArrayAllocations()
//
bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt, GenTreeCall* call)
{
 if (!call->IsHelperCall())
 {
 return false;
 }

 const CorInfoHelpFunc helper = call->GetHelperNum();
 int lengthArgIndex = -1;
 int typeArgIndex = -1;
 int lengthArgIndex = -1;
 int typeArgIndex = -1;
 unsigned lengthOffset = 0;

switch (helper)
if (call->IsHelperCall())
 {
 case CORINFO_HELP_NEWARR_1_DIRECT:
 case CORINFO_HELP_NEWARR_1_VC:
 case CORINFO_HELP_NEWARR_1_PTR:
 case CORINFO_HELP_NEWARR_1_ALIGN8:
 lengthArgIndex = 1;
 typeArgIndex = 0;
 break;
 switch (call->GetHelperNum())
 {
 case CORINFO_HELP_NEWARR_1_DIRECT:
 case CORINFO_HELP_NEWARR_1_VC:
 case CORINFO_HELP_NEWARR_1_PTR:
 case CORINFO_HELP_NEWARR_1_ALIGN8:
 lengthArgIndex = 1;
 typeArgIndex = 0;
 lengthOffset = OFFSETOF__CORINFO_Array__length;
 break;

 default:
 return false;
 default:
 return false;
 }
 }
 else if (call->IsSpecialIntrinsic(this, NI_System_String_FastAllocateString))
 {
 // Strings are modelled as FastAllocateString(pMT, length) and reuse the array
 // stack allocation path; only the length field offset differs.
 //
 lengthArgIndex = 1;
 typeArgIndex = 0;
 lengthOffset = OFFSETOF__CORINFO_String__stringLen;
 }
 else
 {
 return false;
 }

 // If this is a local array, the new helper will have an arg for the array's address
 // If this is a local array or string, the call will have an arg for the object's address
 //
 CallArg* const stackLocalAddressArg = call->gtArgs.FindWellKnownArg(WellKnownArg::StackArrayLocal);

Expand All@@ -2880,7 +2892,7 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,
 return false;
 }

 JITDUMP("Expanding new array helper for stack allocated array at [%06d] in " FMT_BB ":\n", dspTreeID(call),
 JITDUMP("Expanding new array/string helper for stack allocated object at [%06d] in " FMT_BB ":\n", dspTreeID(call),
 block->bbNum);
 DISPTREE(call);
 JITDUMP("\n");
Expand All@@ -2900,22 +2912,22 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,

 GenTree* const stackLocalAddress = stackLocalAddressArg->GetNode();

 // Initialize the array method table pointer.
 // Initialize the method table pointer.
 //
 GenTree* const mt = call->gtArgs.GetArgByIndex(typeArgIndex)->GetNode();
 GenTree* const mtStore = gtNewStoreValueNode(TYP_I_IMPL, stackLocalAddress, mt);
 Statement* const mtStmt = fgNewStmtFromTree(mtStore);

 fgInsertStmtBefore(block, stmt, mtStmt);

 // Initialize the array length.
 // Initialize the array/string length.
 //
 GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
 GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
 GenTree* const lengthAddress = gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress),
gtNewIconNode(OFFSETOF__CORINFO_Array__length, TYP_I_IMPL));
 GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
 Statement* const lenStmt = fgNewStmtFromTree(lengthStore);
 GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
 GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
 GenTree* const lengthAddress =
gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress), gtNewIconNode(lengthOffset, TYP_I_IMPL));
 GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
 Statement* const lenStmt = fgNewStmtFromTree(lengthStore);

 fgInsertStmtBefore(block, stmt, lenStmt);

Expand Down

6 changes: 6 additions & 0 deletions
src/coreclr/jit/importercalls.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -4148,7 +4148,13 @@ GenTree* Compiler::impIntrinsic(CORINFO_CLASS_HANDLE clsHnd,
 }

 case NI_System_ArgumentNullException_ThrowIfNull:
 isSpecial = true;
 break;

 case NI_System_String_FastAllocateString:
 // Flag the method so the object allocator runs its escape analysis and can
 // stack allocate non-escaping, constant-length strings.
 optMethodFlags |= OMF_HAS_FASTSTRINGALLOC;
 isSpecial = true;
 break;

Expand Down

1 change: 1 addition & 0 deletions
src/coreclr/jit/jitconfigvalues.h

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -713,6 +713,7 @@ RELEASE_CONFIG_INTEGER(JitObjectStackAllocationBoxedValueClass, "JitObjectStackA
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationConditionalEscape, "JitObjectStackAllocationConditionalEscape", 1)
CONFIG_STRING(JitObjectStackAllocationConditionalEscapeRange, "JitObjectStackAllocationConditionalEscapeRange")
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationArray, "JitObjectStackAllocationArray", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationString, "JitObjectStackAllocationString", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationSize, "JitObjectStackAllocationSize", 528)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationTrackFields, "JitObjectStackAllocationTrackFields", 1)
CONFIG_STRING(JitObjectStackAllocationTrackFieldsRange, "JitObjectStackAllocationTrackFieldsRange")
Expand Down

2 changes: 2 additions & 0 deletions
src/coreclr/jit/jitmetadatalist.h

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -89,6 +89,8 @@ JITMETADATAMETRIC(NewBoxedValueClassHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedBoxedValueClasses, int, 0)
JITMETADATAMETRIC(NewArrayHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedArrays, int, 0)
JITMETADATAMETRIC(NewStringAllocations, int, 0)
JITMETADATAMETRIC(StackAllocatedStrings, int, 0)
JITMETADATAMETRIC(LocalAssertionCount, int, 0)
JITMETADATAMETRIC(LocalAssertionOverflow, int, 0)
JITMETADATAMETRIC(MorphTrackedLocals, int, 0)
Expand Down
Loading
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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JIT: Stack allocate non-escaping strings
#129202
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3198d9e

JIT: Stack allocate non-escaping strings


EgorBo Jun 10, 2026
ef02bad

JIT: Merge string stack-alloc into the array path


EgorBo Jun 10, 2026
622f7fa

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 10, 2026
0858d0a

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 22, 2026
506834d

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 26, 2026
f6bfc0b

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jul 6, 2026
79c4877

JIT: Add FileCheck tests for stack-allocated strings


EgorBo Jul 6, 2026
0f922cb

Potential fix for pull request finding


EgorBo Jul 6, 2026

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1 change: 1 addition & 0 deletions
src/coreclr/jit/compiler.h

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Original file line numberDiff line numberDiff line change
Expand Up@@ -8008,6 +8008,7 @@ class Compiler
#define OMF_HAS_STACK_ARRAY 0x00100000 // Method contains stack allocated arrays
#define OMF_HAS_BOUNDS_CHECKS 0x00200000 // Method contains bounds checks
#define OMF_HAS_EARLY_QMARKS 0x00400000 // Method contains early expandable QMARKs
#define OMF_HAS_FASTSTRINGALLOC 0x00800000 // Method contains String.FastAllocateString calls

 // clang-format on

Expand Down

68 changes: 40 additions & 28 deletions
src/coreclr/jit/helperexpansion.cpp

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Original file line numberDiff line numberDiff line change
Expand Up@@ -2848,30 +2848,42 @@ PhaseStatus Compiler::fgExpandStackArrayAllocations()
//
bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt, GenTreeCall* call)
{
 if (!call->IsHelperCall())
 {
 return false;
 }

 const CorInfoHelpFunc helper = call->GetHelperNum();
 int lengthArgIndex = -1;
 int typeArgIndex = -1;
 int lengthArgIndex = -1;
 int typeArgIndex = -1;
 unsigned lengthOffset = 0;

switch (helper)
if (call->IsHelperCall())
 {
 case CORINFO_HELP_NEWARR_1_DIRECT:
 case CORINFO_HELP_NEWARR_1_VC:
 case CORINFO_HELP_NEWARR_1_PTR:
 case CORINFO_HELP_NEWARR_1_ALIGN8:
 lengthArgIndex = 1;
 typeArgIndex = 0;
 break;
 switch (call->GetHelperNum())
 {
 case CORINFO_HELP_NEWARR_1_DIRECT:
 case CORINFO_HELP_NEWARR_1_VC:
 case CORINFO_HELP_NEWARR_1_PTR:
 case CORINFO_HELP_NEWARR_1_ALIGN8:
 lengthArgIndex = 1;
 typeArgIndex = 0;
 lengthOffset = OFFSETOF__CORINFO_Array__length;
 break;

 default:
 return false;
 default:
 return false;
 }
 }
 else if (call->IsSpecialIntrinsic(this, NI_System_String_FastAllocateString))
 {
 // Strings are modelled as FastAllocateString(pMT, length) and reuse the array
 // stack allocation path; only the length field offset differs.
 //
 lengthArgIndex = 1;
 typeArgIndex = 0;
 lengthOffset = OFFSETOF__CORINFO_String__stringLen;
 }
 else
 {
 return false;
 }

 // If this is a local array, the new helper will have an arg for the array's address
 // If this is a local array or string, the call will have an arg for the object's address
 //
 CallArg* const stackLocalAddressArg = call->gtArgs.FindWellKnownArg(WellKnownArg::StackArrayLocal);

Expand All@@ -2880,7 +2892,7 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,
 return false;
 }

 JITDUMP("Expanding new array helper for stack allocated array at [%06d] in " FMT_BB ":\n", dspTreeID(call),
 JITDUMP("Expanding new array/string helper for stack allocated object at [%06d] in " FMT_BB ":\n", dspTreeID(call),
 block->bbNum);
 DISPTREE(call);
 JITDUMP("\n");
Expand All@@ -2900,22 +2912,22 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,

 GenTree* const stackLocalAddress = stackLocalAddressArg->GetNode();

 // Initialize the array method table pointer.
 // Initialize the method table pointer.
 //
 GenTree* const mt = call->gtArgs.GetArgByIndex(typeArgIndex)->GetNode();
 GenTree* const mtStore = gtNewStoreValueNode(TYP_I_IMPL, stackLocalAddress, mt);
 Statement* const mtStmt = fgNewStmtFromTree(mtStore);

 fgInsertStmtBefore(block, stmt, mtStmt);

 // Initialize the array length.
 // Initialize the array/string length.
 //
 GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
 GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
 GenTree* const lengthAddress = gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress),
gtNewIconNode(OFFSETOF__CORINFO_Array__length, TYP_I_IMPL));
 GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
 Statement* const lenStmt = fgNewStmtFromTree(lengthStore);
 GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
 GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
 GenTree* const lengthAddress =
gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress), gtNewIconNode(lengthOffset, TYP_I_IMPL));
 GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
 Statement* const lenStmt = fgNewStmtFromTree(lengthStore);

 fgInsertStmtBefore(block, stmt, lenStmt);

Expand Down

6 changes: 6 additions & 0 deletions
src/coreclr/jit/importercalls.cpp

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Original file line numberDiff line numberDiff line change
Expand Up@@ -4148,7 +4148,13 @@ GenTree* Compiler::impIntrinsic(CORINFO_CLASS_HANDLE clsHnd,
 }

 case NI_System_ArgumentNullException_ThrowIfNull:
 isSpecial = true;
 break;

 case NI_System_String_FastAllocateString:
 // Flag the method so the object allocator runs its escape analysis and can
 // stack allocate non-escaping, constant-length strings.
 optMethodFlags |= OMF_HAS_FASTSTRINGALLOC;
 isSpecial = true;
 break;

Expand Down

1 change: 1 addition & 0 deletions
src/coreclr/jit/jitconfigvalues.h

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Original file line numberDiff line numberDiff line change
Expand Up@@ -713,6 +713,7 @@ RELEASE_CONFIG_INTEGER(JitObjectStackAllocationBoxedValueClass, "JitObjectStackA
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationConditionalEscape, "JitObjectStackAllocationConditionalEscape", 1)
CONFIG_STRING(JitObjectStackAllocationConditionalEscapeRange, "JitObjectStackAllocationConditionalEscapeRange")
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationArray, "JitObjectStackAllocationArray", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationString, "JitObjectStackAllocationString", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationSize, "JitObjectStackAllocationSize", 528)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationTrackFields, "JitObjectStackAllocationTrackFields", 1)
CONFIG_STRING(JitObjectStackAllocationTrackFieldsRange, "JitObjectStackAllocationTrackFieldsRange")
Expand Down

2 changes: 2 additions & 0 deletions
src/coreclr/jit/jitmetadatalist.h

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Original file line numberDiff line numberDiff line change
Expand Up@@ -89,6 +89,8 @@ JITMETADATAMETRIC(NewBoxedValueClassHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedBoxedValueClasses, int, 0)
JITMETADATAMETRIC(NewArrayHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedArrays, int, 0)
JITMETADATAMETRIC(NewStringAllocations, int, 0)
JITMETADATAMETRIC(StackAllocatedStrings, int, 0)
JITMETADATAMETRIC(LocalAssertionCount, int, 0)
JITMETADATAMETRIC(LocalAssertionOverflow, int, 0)
JITMETADATAMETRIC(MorphTrackedLocals, int, 0)
Expand Down
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
JIT: Stack allocate non-escaping strings#129202

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Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

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 Closed

EgorBo
wants to merge
8
commits into

from

 Closed


JIT: Stack allocate non-escaping strings
#129202
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3198d9e

JIT: Stack allocate non-escaping strings


EgorBo Jun 10, 2026
ef02bad

JIT: Merge string stack-alloc into the array path


EgorBo Jun 10, 2026
622f7fa

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 10, 2026
0858d0a

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 22, 2026
506834d

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 26, 2026
f6bfc0b

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jul 6, 2026
79c4877

JIT: Add FileCheck tests for stack-allocated strings


EgorBo Jul 6, 2026
0f922cb

Potential fix for pull request finding


EgorBo Jul 6, 2026

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1 change: 1 addition & 0 deletions
src/coreclr/jit/compiler.h

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -8008,6 +8008,7 @@ class Compiler
#define OMF_HAS_STACK_ARRAY 0x00100000 // Method contains stack allocated arrays
#define OMF_HAS_BOUNDS_CHECKS 0x00200000 // Method contains bounds checks
#define OMF_HAS_EARLY_QMARKS 0x00400000 // Method contains early expandable QMARKs
#define OMF_HAS_FASTSTRINGALLOC 0x00800000 // Method contains String.FastAllocateString calls

 // clang-format on

Expand Down

68 changes: 40 additions & 28 deletions
src/coreclr/jit/helperexpansion.cpp

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2848,30 +2848,42 @@ PhaseStatus Compiler::fgExpandStackArrayAllocations()
//
bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt, GenTreeCall* call)
{
 if (!call->IsHelperCall())
 {
 return false;
 }

 const CorInfoHelpFunc helper = call->GetHelperNum();
 int lengthArgIndex = -1;
 int typeArgIndex = -1;
 int lengthArgIndex = -1;
 int typeArgIndex = -1;
 unsigned lengthOffset = 0;

switch (helper)
if (call->IsHelperCall())
 {
 case CORINFO_HELP_NEWARR_1_DIRECT:
 case CORINFO_HELP_NEWARR_1_VC:
 case CORINFO_HELP_NEWARR_1_PTR:
 case CORINFO_HELP_NEWARR_1_ALIGN8:
 lengthArgIndex = 1;
 typeArgIndex = 0;
 break;
 switch (call->GetHelperNum())
 {
 case CORINFO_HELP_NEWARR_1_DIRECT:
 case CORINFO_HELP_NEWARR_1_VC:
 case CORINFO_HELP_NEWARR_1_PTR:
 case CORINFO_HELP_NEWARR_1_ALIGN8:
 lengthArgIndex = 1;
 typeArgIndex = 0;
 lengthOffset = OFFSETOF__CORINFO_Array__length;
 break;

 default:
 return false;
 default:
 return false;
 }
 }
 else if (call->IsSpecialIntrinsic(this, NI_System_String_FastAllocateString))
 {
 // Strings are modelled as FastAllocateString(pMT, length) and reuse the array
 // stack allocation path; only the length field offset differs.
 //
 lengthArgIndex = 1;
 typeArgIndex = 0;
 lengthOffset = OFFSETOF__CORINFO_String__stringLen;
 }
 else
 {
 return false;
 }

 // If this is a local array, the new helper will have an arg for the array's address
 // If this is a local array or string, the call will have an arg for the object's address
 //
 CallArg* const stackLocalAddressArg = call->gtArgs.FindWellKnownArg(WellKnownArg::StackArrayLocal);

Expand All@@ -2880,7 +2892,7 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,
 return false;
 }

 JITDUMP("Expanding new array helper for stack allocated array at [%06d] in " FMT_BB ":\n", dspTreeID(call),
 JITDUMP("Expanding new array/string helper for stack allocated object at [%06d] in " FMT_BB ":\n", dspTreeID(call),
 block->bbNum);
 DISPTREE(call);
 JITDUMP("\n");
Expand All@@ -2900,22 +2912,22 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,

 GenTree* const stackLocalAddress = stackLocalAddressArg->GetNode();

 // Initialize the array method table pointer.
 // Initialize the method table pointer.
 //
 GenTree* const mt = call->gtArgs.GetArgByIndex(typeArgIndex)->GetNode();
 GenTree* const mtStore = gtNewStoreValueNode(TYP_I_IMPL, stackLocalAddress, mt);
 Statement* const mtStmt = fgNewStmtFromTree(mtStore);

 fgInsertStmtBefore(block, stmt, mtStmt);

 // Initialize the array length.
 // Initialize the array/string length.
 //
 GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
 GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
 GenTree* const lengthAddress = gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress),
gtNewIconNode(OFFSETOF__CORINFO_Array__length, TYP_I_IMPL));
 GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
 Statement* const lenStmt = fgNewStmtFromTree(lengthStore);
 GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
 GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
 GenTree* const lengthAddress =
gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress), gtNewIconNode(lengthOffset, TYP_I_IMPL));
 GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
 Statement* const lenStmt = fgNewStmtFromTree(lengthStore);

 fgInsertStmtBefore(block, stmt, lenStmt);

Expand Down

6 changes: 6 additions & 0 deletions
src/coreclr/jit/importercalls.cpp

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Original file line numberDiff line numberDiff line change
Expand Up@@ -4148,7 +4148,13 @@ GenTree* Compiler::impIntrinsic(CORINFO_CLASS_HANDLE clsHnd,
 }

 case NI_System_ArgumentNullException_ThrowIfNull:
 isSpecial = true;
 break;

 case NI_System_String_FastAllocateString:
 // Flag the method so the object allocator runs its escape analysis and can
 // stack allocate non-escaping, constant-length strings.
 optMethodFlags |= OMF_HAS_FASTSTRINGALLOC;
 isSpecial = true;
 break;

Expand Down

1 change: 1 addition & 0 deletions
src/coreclr/jit/jitconfigvalues.h

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -713,6 +713,7 @@ RELEASE_CONFIG_INTEGER(JitObjectStackAllocationBoxedValueClass, "JitObjectStackA
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationConditionalEscape, "JitObjectStackAllocationConditionalEscape", 1)
CONFIG_STRING(JitObjectStackAllocationConditionalEscapeRange, "JitObjectStackAllocationConditionalEscapeRange")
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationArray, "JitObjectStackAllocationArray", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationString, "JitObjectStackAllocationString", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationSize, "JitObjectStackAllocationSize", 528)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationTrackFields, "JitObjectStackAllocationTrackFields", 1)
CONFIG_STRING(JitObjectStackAllocationTrackFieldsRange, "JitObjectStackAllocationTrackFieldsRange")
Expand Down

2 changes: 2 additions & 0 deletions
src/coreclr/jit/jitmetadatalist.h

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Original file line numberDiff line numberDiff line change
Expand Up@@ -89,6 +89,8 @@ JITMETADATAMETRIC(NewBoxedValueClassHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedBoxedValueClasses, int, 0)
JITMETADATAMETRIC(NewArrayHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedArrays, int, 0)
JITMETADATAMETRIC(NewStringAllocations, int, 0)
JITMETADATAMETRIC(StackAllocatedStrings, int, 0)
JITMETADATAMETRIC(LocalAssertionCount, int, 0)
JITMETADATAMETRIC(LocalAssertionOverflow, int, 0)
JITMETADATAMETRIC(MorphTrackedLocals, int, 0)
Expand Down
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

Skip to content
JIT: Stack allocate non-escaping strings#129202

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 Closed

EgorBo
wants to merge
8
commits into

from

 Closed


JIT: Stack allocate non-escaping strings
#129202
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3198d9e

JIT: Stack allocate non-escaping strings


EgorBo Jun 10, 2026
ef02bad

JIT: Merge string stack-alloc into the array path


EgorBo Jun 10, 2026
622f7fa

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 10, 2026
0858d0a

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 22, 2026
506834d

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jun 26, 2026
f6bfc0b

Merge branch 'main' into egorbo/jit-stackalloc-strings


EgorBo Jul 6, 2026
79c4877

JIT: Add FileCheck tests for stack-allocated strings


EgorBo Jul 6, 2026
0f922cb

Potential fix for pull request finding


EgorBo Jul 6, 2026

File filter

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1 change: 1 addition & 0 deletions
src/coreclr/jit/compiler.h

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -8008,6 +8008,7 @@ class Compiler
#define OMF_HAS_STACK_ARRAY 0x00100000 // Method contains stack allocated arrays
#define OMF_HAS_BOUNDS_CHECKS 0x00200000 // Method contains bounds checks
#define OMF_HAS_EARLY_QMARKS 0x00400000 // Method contains early expandable QMARKs
#define OMF_HAS_FASTSTRINGALLOC 0x00800000 // Method contains String.FastAllocateString calls

 // clang-format on

Expand Down

68 changes: 40 additions & 28 deletions
src/coreclr/jit/helperexpansion.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2848,30 +2848,42 @@ PhaseStatus Compiler::fgExpandStackArrayAllocations()
//
bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt, GenTreeCall* call)
{
 if (!call->IsHelperCall())
 {
 return false;
 }

 const CorInfoHelpFunc helper = call->GetHelperNum();
 int lengthArgIndex = -1;
 int typeArgIndex = -1;
 int lengthArgIndex = -1;
 int typeArgIndex = -1;
 unsigned lengthOffset = 0;

switch (helper)
if (call->IsHelperCall())
 {
 case CORINFO_HELP_NEWARR_1_DIRECT:
 case CORINFO_HELP_NEWARR_1_VC:
 case CORINFO_HELP_NEWARR_1_PTR:
 case CORINFO_HELP_NEWARR_1_ALIGN8:
 lengthArgIndex = 1;
 typeArgIndex = 0;
 break;
 switch (call->GetHelperNum())
 {
 case CORINFO_HELP_NEWARR_1_DIRECT:
 case CORINFO_HELP_NEWARR_1_VC:
 case CORINFO_HELP_NEWARR_1_PTR:
 case CORINFO_HELP_NEWARR_1_ALIGN8:
 lengthArgIndex = 1;
 typeArgIndex = 0;
 lengthOffset = OFFSETOF__CORINFO_Array__length;
 break;

 default:
 return false;
 default:
 return false;
 }
 }
 else if (call->IsSpecialIntrinsic(this, NI_System_String_FastAllocateString))
 {
 // Strings are modelled as FastAllocateString(pMT, length) and reuse the array
 // stack allocation path; only the length field offset differs.
 //
 lengthArgIndex = 1;
 typeArgIndex = 0;
 lengthOffset = OFFSETOF__CORINFO_String__stringLen;
 }
 else
 {
 return false;
 }

 // If this is a local array, the new helper will have an arg for the array's address
 // If this is a local array or string, the call will have an arg for the object's address
 //
 CallArg* const stackLocalAddressArg = call->gtArgs.FindWellKnownArg(WellKnownArg::StackArrayLocal);

Expand All@@ -2880,7 +2892,7 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,
 return false;
 }

 JITDUMP("Expanding new array helper for stack allocated array at [%06d] in " FMT_BB ":\n", dspTreeID(call),
 JITDUMP("Expanding new array/string helper for stack allocated object at [%06d] in " FMT_BB ":\n", dspTreeID(call),
 block->bbNum);
 DISPTREE(call);
 JITDUMP("\n");
Expand All@@ -2900,22 +2912,22 @@ bool Compiler::fgExpandStackArrayAllocation(BasicBlock* block, Statement* stmt,

 GenTree* const stackLocalAddress = stackLocalAddressArg->GetNode();

 // Initialize the array method table pointer.
 // Initialize the method table pointer.
 //
 GenTree* const mt = call->gtArgs.GetArgByIndex(typeArgIndex)->GetNode();
 GenTree* const mtStore = gtNewStoreValueNode(TYP_I_IMPL, stackLocalAddress, mt);
 Statement* const mtStmt = fgNewStmtFromTree(mtStore);

 fgInsertStmtBefore(block, stmt, mtStmt);

 // Initialize the array length.
 // Initialize the array/string length.
 //
 GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
 GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
 GenTree* const lengthAddress = gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress),
gtNewIconNode(OFFSETOF__CORINFO_Array__length, TYP_I_IMPL));
 GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
 Statement* const lenStmt = fgNewStmtFromTree(lengthStore);
 GenTree* const lengthArg = call->gtArgs.GetArgByIndex(lengthArgIndex)->GetNode();
 GenTree* const lengthArgInt = fgOptimizeCast(gtNewCastNode(TYP_INT, lengthArg, false, TYP_INT));
 GenTree* const lengthAddress =
gtNewOperNode(GT_ADD, TYP_I_IMPL, gtCloneExpr(stackLocalAddress), gtNewIconNode(lengthOffset, TYP_I_IMPL));
 GenTree* const lengthStore = gtNewStoreValueNode(TYP_INT, lengthAddress, lengthArgInt);
 Statement* const lenStmt = fgNewStmtFromTree(lengthStore);

 fgInsertStmtBefore(block, stmt, lenStmt);

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6 changes: 6 additions & 0 deletions
src/coreclr/jit/importercalls.cpp

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Original file line numberDiff line numberDiff line change
Expand Up@@ -4148,7 +4148,13 @@ GenTree* Compiler::impIntrinsic(CORINFO_CLASS_HANDLE clsHnd,
 }

 case NI_System_ArgumentNullException_ThrowIfNull:
 isSpecial = true;
 break;

 case NI_System_String_FastAllocateString:
 // Flag the method so the object allocator runs its escape analysis and can
 // stack allocate non-escaping, constant-length strings.
 optMethodFlags |= OMF_HAS_FASTSTRINGALLOC;
 isSpecial = true;
 break;

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1 change: 1 addition & 0 deletions
src/coreclr/jit/jitconfigvalues.h

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Original file line numberDiff line numberDiff line change
Expand Up@@ -713,6 +713,7 @@ RELEASE_CONFIG_INTEGER(JitObjectStackAllocationBoxedValueClass, "JitObjectStackA
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationConditionalEscape, "JitObjectStackAllocationConditionalEscape", 1)
CONFIG_STRING(JitObjectStackAllocationConditionalEscapeRange, "JitObjectStackAllocationConditionalEscapeRange")
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationArray, "JitObjectStackAllocationArray", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationString, "JitObjectStackAllocationString", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationSize, "JitObjectStackAllocationSize", 528)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationTrackFields, "JitObjectStackAllocationTrackFields", 1)
CONFIG_STRING(JitObjectStackAllocationTrackFieldsRange, "JitObjectStackAllocationTrackFieldsRange")
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2 changes: 2 additions & 0 deletions
src/coreclr/jit/jitmetadatalist.h

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Original file line numberDiff line numberDiff line change
Expand Up@@ -89,6 +89,8 @@ JITMETADATAMETRIC(NewBoxedValueClassHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedBoxedValueClasses, int, 0)
JITMETADATAMETRIC(NewArrayHelperCalls, int, 0)
JITMETADATAMETRIC(StackAllocatedArrays, int, 0)
JITMETADATAMETRIC(NewStringAllocations, int, 0)
JITMETADATAMETRIC(StackAllocatedStrings, int, 0)
JITMETADATAMETRIC(LocalAssertionCount, int, 0)
JITMETADATAMETRIC(LocalAssertionOverflow, int, 0)
JITMETADATAMETRIC(MorphTrackedLocals, int, 0)
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