Skip to content

JIT: Enable implicit tailcalls for tail-awaits#129255

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

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
jakobbotsch merged 7 commits into from
Jul 1, 2026
Merged

JIT: Enable implicit tailcalls for tail-awaits #129255

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
7 commits
Select commit Hold shift + click to select a range
dcda86e
JIT: Enable implicit tailcalls for tail-awaits
jakobbotsch Jun 10, 2026
2eb525c
Feedback
jakobbotsch Jun 11, 2026
6f6428c
Merge branch 'main' into real-tailcall-for-tailawaits
jakobbotsch Jun 26, 2026
d4603a8
Fix
jakobbotsch Jun 26, 2026
4fc43ab
Also allow TransparentAwait
jakobbotsch Jun 26, 2026
653e982
Reset tailcall prefix flag before importing RET in async version
jakobbotsch Jun 27, 2026
0d7296d
Address feedback, remove unnecessary check
jakobbotsch Jun 29, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
14 changes: 13 additions & 1 deletion src/coreclr/jit/importer.cpp
View file
Open in desktop
Original file line numberDiff line numberDiff line change
Expand Up@@ -4602,7 +4602,8 @@ bool Compiler::impIsImplicitTailCallCandidate(
#endif // !FEATURE_TAILCALL_OPT_SHARED_RETURN

// must be call+ret or call+pop+ret
if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive))
if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive) &&
((prefixFlags & PREFIX_IS_ASYNC_VERSION_TAIL_AWAIT) == 0))
{
return false;
}
Expand DownExpand Up@@ -9331,6 +9332,7 @@ void Compiler::impImportBlockCode(BasicBlock* block)
impAppendTree(gtUnusedValNode(val), CHECK_SPILL_ALL, impCurStmtDI);
}

prefixFlags &= ~PREFIX_TAILCALL;
goto RET;
}

Expand DownExpand Up@@ -11784,6 +11786,16 @@ bool Compiler::impWrapTopOfStackInAwait()
if (impInlineRoot()->compIsAsyncVersion())
{
asyncInfo->IsTailAwait = !compIsForInlining() || impInlineInfo->iciCall->GetAsyncInfo().IsTailAwait;

#if FEATURE_TAILCALL_OPT
// We intentionally do not consult with the EE and canTailCall because
// this is us introducing a call as an implementation detail and not a
// user-introduced call.
if (asyncInfo->IsTailAwait && opts.compTailCallOpt && opts.OptimizationEnabled())
{
awaitCall->gtCallMoreFlags |= GTF_CALL_M_IMPLICIT_TAILCALL;
}
#endif
Comment thread
jakobbotsch marked this conversation as resolved.
}
else
{
Expand Down
18 changes: 12 additions & 6 deletions src/coreclr/jit/importercalls.cpp
View file
Open in desktop
Original file line numberDiff line numberDiff line change
Expand Up@@ -66,7 +66,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
// to see any imperative security.
// Reverse P/Invokes need a call to CORINFO_HELP_JIT_REVERSE_PINVOKE_EXIT
// at the end, so tailcalls should be disabled.
// Async methods need to restore contexts, so tailcalls should be disabled.
if (info.compFlags & CORINFO_FLG_SYNCH)
{
canTailCall = false;
Expand All@@ -77,11 +76,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
canTailCall = false;
szCanTailCallFailReason = "Caller is Reverse P/Invoke";
}
else if (compIsAsync())
{
canTailCall = false;
szCanTailCallFailReason = "Caller is async method";
}
#if !FEATURE_FIXED_OUT_ARGS
else if (info.compIsVarArgs)
{
Expand DownExpand Up@@ -1141,6 +1135,18 @@ var_types Compiler::impImportCall(OPCODE opcode,
BADCODE("Stack should be empty after tailcall");
}

// Async methods need to restore contexts, so in general tailcalls
// should be disabled. The exception is a tail await: for those the JIT
// directly returns the callee's continuation to the caller and no
// context needs to be restored, so the async call can be turned into a
// real tail call. Any other tail call candidate in an async method
// must be disqualified.
if (canTailCall && compIsAsync() && (!call->AsCall()->IsAsync() || !call->AsCall()->GetAsyncInfo().IsTailAwait))
{
canTailCall = false;
szCanTailCallFailReason = "Caller is async method and call is not a tail await";
}
Comment thread
jakobbotsch marked this conversation as resolved.
Comment thread
jakobbotsch marked this conversation as resolved.
Comment thread
jakobbotsch marked this conversation as resolved.

// For opportunistic tailcalls we allow implicit widening, i.e. tailcalls from int32 -> int16, since the
// managed calling convention dictates that the callee widens the value. For explicit tailcalls or async
// functions we don't want to require this detail of the calling convention to bubble up to helper
Expand Down
Loading
, 'i'); if (__m === '*' || __re.test(location.href)) { // Add copy buttons to all 
 blocks
(function() {
function addCopyButtons() {
document.querySelectorAll('pre code').forEach(function(codeBlock) {
if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;
codeBlock.parentElement.setAttribute('data-copy-added', 'true');
var btn = document.createElement('button');
btn.textContent = 'Copy';
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;';
btn.onmouseover = function() { this.style.opacity = '1'; };
btn.onmouseout = function() { this.style.opacity = '0.7'; };
btn.onclick = function() {
navigator.clipboard.writeText(codeBlock.textContent).then(function() {
btn.textContent = 'Copied!';
setTimeout(function() { btn.textContent = 'Copy'; }, 1500);
});
};
codeBlock.parentElement.style.position = 'relative';
codeBlock.parentElement.appendChild(btn);
});
}
addCopyButtons();
// Re-run on dynamic content
var observer = new MutationObserver(addCopyButtons);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '
JIT: Enable implicit tailcalls for tail-awaits by jakobbotsch · Pull Request #129255 · dotnet/runtime · GitHub
Skip to content
JIT: Enable implicit tailcalls for tail-awaits#129255

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

By clicking “Sign up for GitHub”, you agree to our terms of service and
privacy statement. We’ll occasionally send you account related emails.

Already on GitHub?
Sign in
to your account

 Merged

jakobbotsch
merged 7 commits into

from

Jul 1, 2026
 Merged


JIT: Enable implicit tailcalls for tail-awaits
#129255
Show file tree
Hide file tree
 Changes from all commits
Commits

Show all changes


7 commits


Select commit
Hold shift + click to select a range
dcda86e

JIT: Enable implicit tailcalls for tail-awaits


jakobbotsch Jun 10, 2026
2eb525c

Feedback


jakobbotsch Jun 11, 2026
6f6428c

Merge branch 'main' into real-tailcall-for-tailawaits


jakobbotsch Jun 26, 2026
d4603a8

Fix


jakobbotsch Jun 26, 2026
4fc43ab

Also allow TransparentAwait


jakobbotsch Jun 26, 2026
653e982

Reset tailcall prefix flag before importing RET in async version


jakobbotsch Jun 27, 2026
0d7296d

Address feedback, remove unnecessary check


jakobbotsch Jun 29, 2026

File filter

Filter by extension
Filter by extension
Conversations

Failed to load comments. 
Loading
Jump to

Jump to file


Failed to load files. 
Loading
 Diff view

 Diff view


14 changes: 13 additions & 1 deletion
src/coreclr/jit/importer.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -4602,7 +4602,8 @@ bool Compiler::impIsImplicitTailCallCandidate(
#endif // !FEATURE_TAILCALL_OPT_SHARED_RETURN

 // must be call+ret or call+pop+ret
 if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive))
 if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive) &&
 ((prefixFlags & PREFIX_IS_ASYNC_VERSION_TAIL_AWAIT) == 0))
 {
 return false;
 }
Expand DownExpand Up@@ -9331,6 +9332,7 @@ void Compiler::impImportBlockCode(BasicBlock* block)
 impAppendTree(gtUnusedValNode(val), CHECK_SPILL_ALL, impCurStmtDI);
 }

 prefixFlags &= ~PREFIX_TAILCALL;
 goto RET;
 }

Expand DownExpand Up@@ -11784,6 +11786,16 @@ bool Compiler::impWrapTopOfStackInAwait()
 if (impInlineRoot()->compIsAsyncVersion())
 {
 asyncInfo->IsTailAwait = !compIsForInlining() || impInlineInfo->iciCall->GetAsyncInfo().IsTailAwait;

#if FEATURE_TAILCALL_OPT
 // We intentionally do not consult with the EE and canTailCall because
 // this is us introducing a call as an implementation detail and not a
 // user-introduced call.
 if (asyncInfo->IsTailAwait && opts.compTailCallOpt && opts.OptimizationEnabled())
 {
 awaitCall->gtCallMoreFlags |= GTF_CALL_M_IMPLICIT_TAILCALL;
 }
#endif
Comment thread
jakobbotsch marked this conversation as resolved.

 }
 else
 {
Expand Down

18 changes: 12 additions & 6 deletions
src/coreclr/jit/importercalls.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -66,7 +66,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
 // to see any imperative security.
 // Reverse P/Invokes need a call to CORINFO_HELP_JIT_REVERSE_PINVOKE_EXIT
 // at the end, so tailcalls should be disabled.
 // Async methods need to restore contexts, so tailcalls should be disabled.
 if (info.compFlags & CORINFO_FLG_SYNCH)
 {
 canTailCall = false;
Expand All@@ -77,11 +76,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
 canTailCall = false;
 szCanTailCallFailReason = "Caller is Reverse P/Invoke";
 }
 else if (compIsAsync())
 {
 canTailCall = false;
 szCanTailCallFailReason = "Caller is async method";
 }
#if !FEATURE_FIXED_OUT_ARGS
 else if (info.compIsVarArgs)
 {
Expand DownExpand Up@@ -1141,6 +1135,18 @@ var_types Compiler::impImportCall(OPCODE opcode,
 BADCODE("Stack should be empty after tailcall");
 }

 // Async methods need to restore contexts, so in general tailcalls
 // should be disabled. The exception is a tail await: for those the JIT
 // directly returns the callee's continuation to the caller and no
 // context needs to be restored, so the async call can be turned into a
 // real tail call. Any other tail call candidate in an async method
 // must be disqualified.
 if (canTailCall && compIsAsync() && (!call->AsCall()->IsAsync() || !call->AsCall()->GetAsyncInfo().IsTailAwait))
 {
 canTailCall = false;
 szCanTailCallFailReason = "Caller is async method and call is not a tail await";
 }
Comment thread
jakobbotsch marked this conversation as resolved.

Comment thread
jakobbotsch marked this conversation as resolved.

Comment thread
jakobbotsch marked this conversation as resolved.


 // For opportunistic tailcalls we allow implicit widening, i.e. tailcalls from int32 -> int16, since the
 // managed calling convention dictates that the callee widens the value. For explicit tailcalls or async
 // functions we don't want to require this detail of the calling convention to bubble up to helper
Expand Down
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Force GitHub README to respect dark mode
(function() {
var style = document.createElement('style');
style.textContent = '
.markdown-body {
color-scheme: dark light;
}
.markdown-body pre { background: #161b22 !important; }
.markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }
.markdown-body table th, .markdown-body table td { border-color: #30363d !important; }
.markdown-body img { background: #0d1117; }
.markdown-body blockquote { border-left-color: #8b949e; }
.markdown-body hr { border-color: #30363d; }
';
document.head.appendChild(style);
})();
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
JIT: Enable implicit tailcalls for tail-awaits by jakobbotsch · Pull Request #129255 · dotnet/runtime · GitHub
Skip to content
JIT: Enable implicit tailcalls for tail-awaits#129255

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

By clicking “Sign up for GitHub”, you agree to our terms of service and
privacy statement. We’ll occasionally send you account related emails.

Already on GitHub?
Sign in
to your account

 Merged

jakobbotsch
merged 7 commits into

from

Jul 1, 2026
 Merged


JIT: Enable implicit tailcalls for tail-awaits
#129255
Show file tree
Hide file tree
 Changes from all commits
Commits

Show all changes


7 commits


Select commit
Hold shift + click to select a range
dcda86e

JIT: Enable implicit tailcalls for tail-awaits


jakobbotsch Jun 10, 2026
2eb525c

Feedback


jakobbotsch Jun 11, 2026
6f6428c

Merge branch 'main' into real-tailcall-for-tailawaits


jakobbotsch Jun 26, 2026
d4603a8

Fix


jakobbotsch Jun 26, 2026
4fc43ab

Also allow TransparentAwait


jakobbotsch Jun 26, 2026
653e982

Reset tailcall prefix flag before importing RET in async version


jakobbotsch Jun 27, 2026
0d7296d

Address feedback, remove unnecessary check


jakobbotsch Jun 29, 2026

File filter

Filter by extension
Filter by extension
Conversations

Failed to load comments. 
Loading
Jump to

Jump to file


Failed to load files. 
Loading
 Diff view

 Diff view


14 changes: 13 additions & 1 deletion
src/coreclr/jit/importer.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -4602,7 +4602,8 @@ bool Compiler::impIsImplicitTailCallCandidate(
#endif // !FEATURE_TAILCALL_OPT_SHARED_RETURN

 // must be call+ret or call+pop+ret
 if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive))
 if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive) &&
 ((prefixFlags & PREFIX_IS_ASYNC_VERSION_TAIL_AWAIT) == 0))
 {
 return false;
 }
Expand DownExpand Up@@ -9331,6 +9332,7 @@ void Compiler::impImportBlockCode(BasicBlock* block)
 impAppendTree(gtUnusedValNode(val), CHECK_SPILL_ALL, impCurStmtDI);
 }

 prefixFlags &= ~PREFIX_TAILCALL;
 goto RET;
 }

Expand DownExpand Up@@ -11784,6 +11786,16 @@ bool Compiler::impWrapTopOfStackInAwait()
 if (impInlineRoot()->compIsAsyncVersion())
 {
 asyncInfo->IsTailAwait = !compIsForInlining() || impInlineInfo->iciCall->GetAsyncInfo().IsTailAwait;

#if FEATURE_TAILCALL_OPT
 // We intentionally do not consult with the EE and canTailCall because
 // this is us introducing a call as an implementation detail and not a
 // user-introduced call.
 if (asyncInfo->IsTailAwait && opts.compTailCallOpt && opts.OptimizationEnabled())
 {
 awaitCall->gtCallMoreFlags |= GTF_CALL_M_IMPLICIT_TAILCALL;
 }
#endif
Comment thread
jakobbotsch marked this conversation as resolved.

 }
 else
 {
Expand Down

18 changes: 12 additions & 6 deletions
src/coreclr/jit/importercalls.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -66,7 +66,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
 // to see any imperative security.
 // Reverse P/Invokes need a call to CORINFO_HELP_JIT_REVERSE_PINVOKE_EXIT
 // at the end, so tailcalls should be disabled.
 // Async methods need to restore contexts, so tailcalls should be disabled.
 if (info.compFlags & CORINFO_FLG_SYNCH)
 {
 canTailCall = false;
Expand All@@ -77,11 +76,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
 canTailCall = false;
 szCanTailCallFailReason = "Caller is Reverse P/Invoke";
 }
 else if (compIsAsync())
 {
 canTailCall = false;
 szCanTailCallFailReason = "Caller is async method";
 }
#if !FEATURE_FIXED_OUT_ARGS
 else if (info.compIsVarArgs)
 {
Expand DownExpand Up@@ -1141,6 +1135,18 @@ var_types Compiler::impImportCall(OPCODE opcode,
 BADCODE("Stack should be empty after tailcall");
 }

 // Async methods need to restore contexts, so in general tailcalls
 // should be disabled. The exception is a tail await: for those the JIT
 // directly returns the callee's continuation to the caller and no
 // context needs to be restored, so the async call can be turned into a
 // real tail call. Any other tail call candidate in an async method
 // must be disqualified.
 if (canTailCall && compIsAsync() && (!call->AsCall()->IsAsync() || !call->AsCall()->GetAsyncInfo().IsTailAwait))
 {
 canTailCall = false;
 szCanTailCallFailReason = "Caller is async method and call is not a tail await";
 }
Comment thread
jakobbotsch marked this conversation as resolved.

Comment thread
jakobbotsch marked this conversation as resolved.

Comment thread
jakobbotsch marked this conversation as resolved.


 // For opportunistic tailcalls we allow implicit widening, i.e. tailcalls from int32 -> int16, since the
 // managed calling convention dictates that the callee widens the value. For explicit tailcalls or async
 // functions we don't want to require this detail of the calling convention to bubble up to helper
Expand Down
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Highlight search terms from Google/DuckDuckGo/Bing referrer
(function() {
var ref = document.referrer;
var terms = [];
if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {
var url = new URL(ref);
var q = url.searchParams.get('q') || url.searchParams.get('p');
if (q) {
terms = q.split(/\s+/).filter(function(t) { return t.length > 2; });
}
}
if (terms.length === 0) return;
var style = document.createElement('style');
style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';
document.head.appendChild(style);
function highlight(node) {
if (node.nodeType === 3) { // text node
var text = node.textContent;
var found = false;
terms.forEach(function(term) {
var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\]\\]/g, '\\') + ')', 'gi');
if (regex.test(text)) {
found = true;
var frag = document.createDocumentFragment();
var parts = text.split(regex);
parts.forEach(function(part, i) {
if (i % 2 === 0) {
frag.appendChild(document.createTextNode(part));
} else {
var span = document.createElement('span');
span.className = 'userscript-highlight';
span.textContent = part;
frag.appendChild(span);
}
});
node.parentNode.replaceChild(frag, node);
}
});
} else if (node.nodeType === 1 && node.childNodes) { // element
var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];
if (!skipTags.includes(node.tagName)) {
Array.from(node.childNodes).forEach(highlight);
}
}
}
highlight(document.body);
// Re-highlight on dynamic content
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1 || node.nodeType === 3) highlight(node);
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
JIT: Enable implicit tailcalls for tail-awaits by jakobbotsch · Pull Request #129255 · dotnet/runtime · GitHub
Skip to content
JIT: Enable implicit tailcalls for tail-awaits#129255

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

By clicking “Sign up for GitHub”, you agree to our terms of service and
privacy statement. We’ll occasionally send you account related emails.

Already on GitHub?
Sign in
to your account

 Merged

jakobbotsch
merged 7 commits into

from

Jul 1, 2026
 Merged


JIT: Enable implicit tailcalls for tail-awaits
#129255
Show file tree
Hide file tree
 Changes from all commits
Commits

Show all changes


7 commits


Select commit
Hold shift + click to select a range
dcda86e

JIT: Enable implicit tailcalls for tail-awaits


jakobbotsch Jun 10, 2026
2eb525c

Feedback


jakobbotsch Jun 11, 2026
6f6428c

Merge branch 'main' into real-tailcall-for-tailawaits


jakobbotsch Jun 26, 2026
d4603a8

Fix


jakobbotsch Jun 26, 2026
4fc43ab

Also allow TransparentAwait


jakobbotsch Jun 26, 2026
653e982

Reset tailcall prefix flag before importing RET in async version


jakobbotsch Jun 27, 2026
0d7296d

Address feedback, remove unnecessary check


jakobbotsch Jun 29, 2026

File filter

Filter by extension
Filter by extension
Conversations

Failed to load comments. 
Loading
Jump to

Jump to file


Failed to load files. 
Loading
 Diff view

 Diff view


14 changes: 13 additions & 1 deletion
src/coreclr/jit/importer.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -4602,7 +4602,8 @@ bool Compiler::impIsImplicitTailCallCandidate(
#endif // !FEATURE_TAILCALL_OPT_SHARED_RETURN

 // must be call+ret or call+pop+ret
 if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive))
 if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive) &&
 ((prefixFlags & PREFIX_IS_ASYNC_VERSION_TAIL_AWAIT) == 0))
 {
 return false;
 }
Expand DownExpand Up@@ -9331,6 +9332,7 @@ void Compiler::impImportBlockCode(BasicBlock* block)
 impAppendTree(gtUnusedValNode(val), CHECK_SPILL_ALL, impCurStmtDI);
 }

 prefixFlags &= ~PREFIX_TAILCALL;
 goto RET;
 }

Expand DownExpand Up@@ -11784,6 +11786,16 @@ bool Compiler::impWrapTopOfStackInAwait()
 if (impInlineRoot()->compIsAsyncVersion())
 {
 asyncInfo->IsTailAwait = !compIsForInlining() || impInlineInfo->iciCall->GetAsyncInfo().IsTailAwait;

#if FEATURE_TAILCALL_OPT
 // We intentionally do not consult with the EE and canTailCall because
 // this is us introducing a call as an implementation detail and not a
 // user-introduced call.
 if (asyncInfo->IsTailAwait && opts.compTailCallOpt && opts.OptimizationEnabled())
 {
 awaitCall->gtCallMoreFlags |= GTF_CALL_M_IMPLICIT_TAILCALL;
 }
#endif
Comment thread
jakobbotsch marked this conversation as resolved.

 }
 else
 {
Expand Down

18 changes: 12 additions & 6 deletions
src/coreclr/jit/importercalls.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -66,7 +66,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
 // to see any imperative security.
 // Reverse P/Invokes need a call to CORINFO_HELP_JIT_REVERSE_PINVOKE_EXIT
 // at the end, so tailcalls should be disabled.
 // Async methods need to restore contexts, so tailcalls should be disabled.
 if (info.compFlags & CORINFO_FLG_SYNCH)
 {
 canTailCall = false;
Expand All@@ -77,11 +76,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
 canTailCall = false;
 szCanTailCallFailReason = "Caller is Reverse P/Invoke";
 }
 else if (compIsAsync())
 {
 canTailCall = false;
 szCanTailCallFailReason = "Caller is async method";
 }
#if !FEATURE_FIXED_OUT_ARGS
 else if (info.compIsVarArgs)
 {
Expand DownExpand Up@@ -1141,6 +1135,18 @@ var_types Compiler::impImportCall(OPCODE opcode,
 BADCODE("Stack should be empty after tailcall");
 }

 // Async methods need to restore contexts, so in general tailcalls
 // should be disabled. The exception is a tail await: for those the JIT
 // directly returns the callee's continuation to the caller and no
 // context needs to be restored, so the async call can be turned into a
 // real tail call. Any other tail call candidate in an async method
 // must be disqualified.
 if (canTailCall && compIsAsync() && (!call->AsCall()->IsAsync() || !call->AsCall()->GetAsyncInfo().IsTailAwait))
 {
 canTailCall = false;
 szCanTailCallFailReason = "Caller is async method and call is not a tail await";
 }
Comment thread
jakobbotsch marked this conversation as resolved.

Comment thread
jakobbotsch marked this conversation as resolved.

Comment thread
jakobbotsch marked this conversation as resolved.


 // For opportunistic tailcalls we allow implicit widening, i.e. tailcalls from int32 -> int16, since the
 // managed calling convention dictates that the callee widens the value. For explicit tailcalls or async
 // functions we don't want to require this detail of the calling convention to bubble up to helper
Expand Down
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Strip utm_, fbclid, gclid, etc. from all links on page
(function() {
var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',
'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
'ref', 'ref_src', 'source', 'medium', 'campaign'];
function cleanUrl(url) {
try {
var u = new URL(url, window.location.origin);
var changed = false;
trackingParams.forEach(function(p) {
if (u.searchParams.has(p)) {
u.searchParams.delete(p);
changed = true;
}
});
return changed ? u.toString() : url;
} catch (e) {
return url;
}
}
function cleanLinks() {
document.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
cleanLinks();
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1) {
if (node.tagName === 'A') cleanLinks();
node.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '
JIT: Enable implicit tailcalls for tail-awaits by jakobbotsch · Pull Request #129255 · dotnet/runtime · GitHub
Skip to content
JIT: Enable implicit tailcalls for tail-awaits#129255

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

By clicking “Sign up for GitHub”, you agree to our terms of service and
privacy statement. We’ll occasionally send you account related emails.

Already on GitHub?
Sign in
to your account

 Merged

jakobbotsch
merged 7 commits into

from

Jul 1, 2026
 Merged


JIT: Enable implicit tailcalls for tail-awaits
#129255
Show file tree
Hide file tree
 Changes from all commits
Commits

Show all changes


7 commits


Select commit
Hold shift + click to select a range
dcda86e

JIT: Enable implicit tailcalls for tail-awaits


jakobbotsch Jun 10, 2026
2eb525c

Feedback


jakobbotsch Jun 11, 2026
6f6428c

Merge branch 'main' into real-tailcall-for-tailawaits


jakobbotsch Jun 26, 2026
d4603a8

Fix


jakobbotsch Jun 26, 2026
4fc43ab

Also allow TransparentAwait


jakobbotsch Jun 26, 2026
653e982

Reset tailcall prefix flag before importing RET in async version


jakobbotsch Jun 27, 2026
0d7296d

Address feedback, remove unnecessary check


jakobbotsch Jun 29, 2026

File filter

Filter by extension
Filter by extension
Conversations

Failed to load comments. 
Loading
Jump to

Jump to file


Failed to load files. 
Loading
 Diff view

 Diff view


14 changes: 13 additions & 1 deletion
src/coreclr/jit/importer.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -4602,7 +4602,8 @@ bool Compiler::impIsImplicitTailCallCandidate(
#endif // !FEATURE_TAILCALL_OPT_SHARED_RETURN

 // must be call+ret or call+pop+ret
 if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive))
 if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive) &&
 ((prefixFlags & PREFIX_IS_ASYNC_VERSION_TAIL_AWAIT) == 0))
 {
 return false;
 }
Expand DownExpand Up@@ -9331,6 +9332,7 @@ void Compiler::impImportBlockCode(BasicBlock* block)
 impAppendTree(gtUnusedValNode(val), CHECK_SPILL_ALL, impCurStmtDI);
 }

 prefixFlags &= ~PREFIX_TAILCALL;
 goto RET;
 }

Expand DownExpand Up@@ -11784,6 +11786,16 @@ bool Compiler::impWrapTopOfStackInAwait()
 if (impInlineRoot()->compIsAsyncVersion())
 {
 asyncInfo->IsTailAwait = !compIsForInlining() || impInlineInfo->iciCall->GetAsyncInfo().IsTailAwait;

#if FEATURE_TAILCALL_OPT
 // We intentionally do not consult with the EE and canTailCall because
 // this is us introducing a call as an implementation detail and not a
 // user-introduced call.
 if (asyncInfo->IsTailAwait && opts.compTailCallOpt && opts.OptimizationEnabled())
 {
 awaitCall->gtCallMoreFlags |= GTF_CALL_M_IMPLICIT_TAILCALL;
 }
#endif
Comment thread
jakobbotsch marked this conversation as resolved.

 }
 else
 {
Expand Down

18 changes: 12 additions & 6 deletions
src/coreclr/jit/importercalls.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -66,7 +66,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
 // to see any imperative security.
 // Reverse P/Invokes need a call to CORINFO_HELP_JIT_REVERSE_PINVOKE_EXIT
 // at the end, so tailcalls should be disabled.
 // Async methods need to restore contexts, so tailcalls should be disabled.
 if (info.compFlags & CORINFO_FLG_SYNCH)
 {
 canTailCall = false;
Expand All@@ -77,11 +76,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
 canTailCall = false;
 szCanTailCallFailReason = "Caller is Reverse P/Invoke";
 }
 else if (compIsAsync())
 {
 canTailCall = false;
 szCanTailCallFailReason = "Caller is async method";
 }
#if !FEATURE_FIXED_OUT_ARGS
 else if (info.compIsVarArgs)
 {
Expand DownExpand Up@@ -1141,6 +1135,18 @@ var_types Compiler::impImportCall(OPCODE opcode,
 BADCODE("Stack should be empty after tailcall");
 }

 // Async methods need to restore contexts, so in general tailcalls
 // should be disabled. The exception is a tail await: for those the JIT
 // directly returns the callee's continuation to the caller and no
 // context needs to be restored, so the async call can be turned into a
 // real tail call. Any other tail call candidate in an async method
 // must be disqualified.
 if (canTailCall && compIsAsync() && (!call->AsCall()->IsAsync() || !call->AsCall()->GetAsyncInfo().IsTailAwait))
 {
 canTailCall = false;
 szCanTailCallFailReason = "Caller is async method and call is not a tail await";
 }
Comment thread
jakobbotsch marked this conversation as resolved.

Comment thread
jakobbotsch marked this conversation as resolved.

Comment thread
jakobbotsch marked this conversation as resolved.


 // For opportunistic tailcalls we allow implicit widening, i.e. tailcalls from int32 -> int16, since the
 // managed calling convention dictates that the callee widens the value. For explicit tailcalls or async
 // functions we don't want to require this detail of the calling convention to bubble up to helper
Expand Down
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
}
}
// Try immediately
tryTheater();
// Try after navigation (SPA)
var lastUrl = location.href;
setInterval(function() {
if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
var observer = new MutationObserver(tryTheater);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
JIT: Enable implicit tailcalls for tail-awaits by jakobbotsch · Pull Request #129255 · dotnet/runtime · GitHub
Skip to content
JIT: Enable implicit tailcalls for tail-awaits#129255

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

By clicking “Sign up for GitHub”, you agree to our terms of service and
privacy statement. We’ll occasionally send you account related emails.

Already on GitHub?
Sign in
to your account

 Merged

jakobbotsch
merged 7 commits into

from

Jul 1, 2026
 Merged


JIT: Enable implicit tailcalls for tail-awaits
#129255
Show file tree
Hide file tree
 Changes from all commits
Commits

Show all changes


7 commits


Select commit
Hold shift + click to select a range
dcda86e

JIT: Enable implicit tailcalls for tail-awaits


jakobbotsch Jun 10, 2026
2eb525c

Feedback


jakobbotsch Jun 11, 2026
6f6428c

Merge branch 'main' into real-tailcall-for-tailawaits


jakobbotsch Jun 26, 2026
d4603a8

Fix


jakobbotsch Jun 26, 2026
4fc43ab

Also allow TransparentAwait


jakobbotsch Jun 26, 2026
653e982

Reset tailcall prefix flag before importing RET in async version


jakobbotsch Jun 27, 2026
0d7296d

Address feedback, remove unnecessary check


jakobbotsch Jun 29, 2026

File filter

Filter by extension
Filter by extension
Conversations

Failed to load comments. 
Loading
Jump to

Jump to file


Failed to load files. 
Loading
 Diff view

 Diff view


14 changes: 13 additions & 1 deletion
src/coreclr/jit/importer.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -4602,7 +4602,8 @@ bool Compiler::impIsImplicitTailCallCandidate(
#endif // !FEATURE_TAILCALL_OPT_SHARED_RETURN

 // must be call+ret or call+pop+ret
 if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive))
 if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive) &&
 ((prefixFlags & PREFIX_IS_ASYNC_VERSION_TAIL_AWAIT) == 0))
 {
 return false;
 }
Expand DownExpand Up@@ -9331,6 +9332,7 @@ void Compiler::impImportBlockCode(BasicBlock* block)
 impAppendTree(gtUnusedValNode(val), CHECK_SPILL_ALL, impCurStmtDI);
 }

 prefixFlags &= ~PREFIX_TAILCALL;
 goto RET;
 }

Expand DownExpand Up@@ -11784,6 +11786,16 @@ bool Compiler::impWrapTopOfStackInAwait()
 if (impInlineRoot()->compIsAsyncVersion())
 {
 asyncInfo->IsTailAwait = !compIsForInlining() || impInlineInfo->iciCall->GetAsyncInfo().IsTailAwait;

#if FEATURE_TAILCALL_OPT
 // We intentionally do not consult with the EE and canTailCall because
 // this is us introducing a call as an implementation detail and not a
 // user-introduced call.
 if (asyncInfo->IsTailAwait && opts.compTailCallOpt && opts.OptimizationEnabled())
 {
 awaitCall->gtCallMoreFlags |= GTF_CALL_M_IMPLICIT_TAILCALL;
 }
#endif
Comment thread
jakobbotsch marked this conversation as resolved.

 }
 else
 {
Expand Down

18 changes: 12 additions & 6 deletions
src/coreclr/jit/importercalls.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -66,7 +66,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
 // to see any imperative security.
 // Reverse P/Invokes need a call to CORINFO_HELP_JIT_REVERSE_PINVOKE_EXIT
 // at the end, so tailcalls should be disabled.
 // Async methods need to restore contexts, so tailcalls should be disabled.
 if (info.compFlags & CORINFO_FLG_SYNCH)
 {
 canTailCall = false;
Expand All@@ -77,11 +76,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
 canTailCall = false;
 szCanTailCallFailReason = "Caller is Reverse P/Invoke";
 }
 else if (compIsAsync())
 {
 canTailCall = false;
 szCanTailCallFailReason = "Caller is async method";
 }
#if !FEATURE_FIXED_OUT_ARGS
 else if (info.compIsVarArgs)
 {
Expand DownExpand Up@@ -1141,6 +1135,18 @@ var_types Compiler::impImportCall(OPCODE opcode,
 BADCODE("Stack should be empty after tailcall");
 }

 // Async methods need to restore contexts, so in general tailcalls
 // should be disabled. The exception is a tail await: for those the JIT
 // directly returns the callee's continuation to the caller and no
 // context needs to be restored, so the async call can be turned into a
 // real tail call. Any other tail call candidate in an async method
 // must be disqualified.
 if (canTailCall && compIsAsync() && (!call->AsCall()->IsAsync() || !call->AsCall()->GetAsyncInfo().IsTailAwait))
 {
 canTailCall = false;
 szCanTailCallFailReason = "Caller is async method and call is not a tail await";
 }
Comment thread
jakobbotsch marked this conversation as resolved.

Comment thread
jakobbotsch marked this conversation as resolved.

Comment thread
jakobbotsch marked this conversation as resolved.


 // For opportunistic tailcalls we allow implicit widening, i.e. tailcalls from int32 -> int16, since the
 // managed calling convention dictates that the callee widens the value. For explicit tailcalls or async
 // functions we don't want to require this detail of the calling convention to bubble up to helper
Expand Down
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Remove or un-stick sticky/fixed headers that block content
(function() {
function unstick() {
document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) {
if (el.style.position === 'fixed' || el.style.position === 'sticky' || getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {
el.style.position = 'static';
el.style.top = 'auto';
el.style.zIndex = 'auto';
}
});
}
unstick();
var observer = new MutationObserver(unstick);
observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });
})();
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
JIT: Enable implicit tailcalls for tail-awaits by jakobbotsch · Pull Request #129255 · dotnet/runtime · GitHub
Skip to content
JIT: Enable implicit tailcalls for tail-awaits#129255

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

By clicking “Sign up for GitHub”, you agree to our terms of service and
privacy statement. We’ll occasionally send you account related emails.

Already on GitHub?
Sign in
to your account

 Merged

jakobbotsch
merged 7 commits into

from

Jul 1, 2026
 Merged


JIT: Enable implicit tailcalls for tail-awaits
#129255
Show file tree
Hide file tree
 Changes from all commits
Commits

Show all changes


7 commits


Select commit
Hold shift + click to select a range
dcda86e

JIT: Enable implicit tailcalls for tail-awaits


jakobbotsch Jun 10, 2026
2eb525c

Feedback


jakobbotsch Jun 11, 2026
6f6428c

Merge branch 'main' into real-tailcall-for-tailawaits


jakobbotsch Jun 26, 2026
d4603a8

Fix


jakobbotsch Jun 26, 2026
4fc43ab

Also allow TransparentAwait


jakobbotsch Jun 26, 2026
653e982

Reset tailcall prefix flag before importing RET in async version


jakobbotsch Jun 27, 2026
0d7296d

Address feedback, remove unnecessary check


jakobbotsch Jun 29, 2026

File filter

Filter by extension
Filter by extension
Conversations

Failed to load comments. 
Loading
Jump to

Jump to file


Failed to load files. 
Loading
 Diff view

 Diff view


14 changes: 13 additions & 1 deletion
src/coreclr/jit/importer.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -4602,7 +4602,8 @@ bool Compiler::impIsImplicitTailCallCandidate(
#endif // !FEATURE_TAILCALL_OPT_SHARED_RETURN

 // must be call+ret or call+pop+ret
 if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive))
 if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive) &&
 ((prefixFlags & PREFIX_IS_ASYNC_VERSION_TAIL_AWAIT) == 0))
 {
 return false;
 }
Expand DownExpand Up@@ -9331,6 +9332,7 @@ void Compiler::impImportBlockCode(BasicBlock* block)
 impAppendTree(gtUnusedValNode(val), CHECK_SPILL_ALL, impCurStmtDI);
 }

 prefixFlags &= ~PREFIX_TAILCALL;
 goto RET;
 }

Expand DownExpand Up@@ -11784,6 +11786,16 @@ bool Compiler::impWrapTopOfStackInAwait()
 if (impInlineRoot()->compIsAsyncVersion())
 {
 asyncInfo->IsTailAwait = !compIsForInlining() || impInlineInfo->iciCall->GetAsyncInfo().IsTailAwait;

#if FEATURE_TAILCALL_OPT
 // We intentionally do not consult with the EE and canTailCall because
 // this is us introducing a call as an implementation detail and not a
 // user-introduced call.
 if (asyncInfo->IsTailAwait && opts.compTailCallOpt && opts.OptimizationEnabled())
 {
 awaitCall->gtCallMoreFlags |= GTF_CALL_M_IMPLICIT_TAILCALL;
 }
#endif
Comment thread
jakobbotsch marked this conversation as resolved.

 }
 else
 {
Expand Down

18 changes: 12 additions & 6 deletions
src/coreclr/jit/importercalls.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -66,7 +66,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
 // to see any imperative security.
 // Reverse P/Invokes need a call to CORINFO_HELP_JIT_REVERSE_PINVOKE_EXIT
 // at the end, so tailcalls should be disabled.
 // Async methods need to restore contexts, so tailcalls should be disabled.
 if (info.compFlags & CORINFO_FLG_SYNCH)
 {
 canTailCall = false;
Expand All@@ -77,11 +76,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
 canTailCall = false;
 szCanTailCallFailReason = "Caller is Reverse P/Invoke";
 }
 else if (compIsAsync())
 {
 canTailCall = false;
 szCanTailCallFailReason = "Caller is async method";
 }
#if !FEATURE_FIXED_OUT_ARGS
 else if (info.compIsVarArgs)
 {
Expand DownExpand Up@@ -1141,6 +1135,18 @@ var_types Compiler::impImportCall(OPCODE opcode,
 BADCODE("Stack should be empty after tailcall");
 }

 // Async methods need to restore contexts, so in general tailcalls
 // should be disabled. The exception is a tail await: for those the JIT
 // directly returns the callee's continuation to the caller and no
 // context needs to be restored, so the async call can be turned into a
 // real tail call. Any other tail call candidate in an async method
 // must be disqualified.
 if (canTailCall && compIsAsync() && (!call->AsCall()->IsAsync() || !call->AsCall()->GetAsyncInfo().IsTailAwait))
 {
 canTailCall = false;
 szCanTailCallFailReason = "Caller is async method and call is not a tail await";
 }
Comment thread
jakobbotsch marked this conversation as resolved.

Comment thread
jakobbotsch marked this conversation as resolved.

Comment thread
jakobbotsch marked this conversation as resolved.


 // For opportunistic tailcalls we allow implicit widening, i.e. tailcalls from int32 -> int16, since the
 // managed calling convention dictates that the callee widens the value. For explicit tailcalls or async
 // functions we don't want to require this detail of the calling convention to bubble up to helper
Expand Down
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Universal Dark Mode - works on any site
(function() {
var enabled = true;
function applyDarkMode() {
if (!enabled) return;
// Create style element if it doesn't exist
var style = document.getElementById('universal-dark-mode-style');
if (!style) {
style = document.createElement('style');
style.id = 'universal-dark-mode-style';
document.head.appendChild(style);
}
// Dark mode CSS - inverts colors but preserves images/video
style.textContent = '
/* Invert everything except media */
html {
filter: invert(1) hue-rotate(180deg) !important;
background: #1a1a2e !important;
}
/* Restore images, videos, iframes, canvas */
img, video, iframe, canvas, svg, picture, [style*="background-image"] {
filter: invert(1) hue-rotate(180deg) !important;
}
/* Preserve specific elements that should not be inverted */
.no-dark-mode, .no-dark-mode *,
[data-theme="light"], [data-theme="light"],
.ace_editor, .ace_editor *,
.CodeMirror, .CodeMirror *,
.monaco-editor, .monaco-editor *,
.markdown-body pre, .markdown-body pre *,
.highlight, .highlight *,
pre code, pre code * {
filter: none !important;
}
/* Fix common UI elements */
.modal, .popup, .dropdown-menu, .tooltip, .popover {
filter: invert(1) hue-rotate(180deg) !important;
background: #2d2d44 !important;
border-color: #444 !important;
}
/* Scrollbars */
::-webkit-scrollbar { background: #1a1a2e !important; }
::-webkit-scrollbar-thumb { background: #444 !important; }
::-webkit-scrollbar-thumb:hover { background: #555 !important; }
/* Selection */
::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
';
}
function removeDarkMode() {
var style = document.getElementById('universal-dark-mode-style');
if (style) style.remove();
}
// Toggle with Alt+Shift+D
document.addEventListener('keydown', function(e) {
if (e.altKey && e.shiftKey && e.key === 'D') {
e.preventDefault();
enabled = !enabled;
if (enabled) {
applyDarkMode();
console.log('[Universal Dark Mode] Enabled');
} else {
removeDarkMode();
console.log('[Universal Dark Mode] Disabled');
}
}
});
// Apply on load
applyDarkMode();
// Re-apply on dynamic content
var observer = new MutationObserver(function(mutations) {
if (enabled && !document.getElementById('universal-dark-mode-style')) {
applyDarkMode();
}
});
observer.observe(document.head, { childList: true });
console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');
})();
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();
JIT: Enable implicit tailcalls for tail-awaits by jakobbotsch · Pull Request #129255 · dotnet/runtime · GitHub
Skip to content
JIT: Enable implicit tailcalls for tail-awaits#129255

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

By clicking “Sign up for GitHub”, you agree to our terms of service and
privacy statement. We’ll occasionally send you account related emails.

Already on GitHub?
Sign in
to your account

 Merged

jakobbotsch
merged 7 commits into

from

Jul 1, 2026
 Merged


JIT: Enable implicit tailcalls for tail-awaits
#129255
Show file tree
Hide file tree
 Changes from all commits
Commits

Show all changes


7 commits


Select commit
Hold shift + click to select a range
dcda86e

JIT: Enable implicit tailcalls for tail-awaits


jakobbotsch Jun 10, 2026
2eb525c

Feedback


jakobbotsch Jun 11, 2026
6f6428c

Merge branch 'main' into real-tailcall-for-tailawaits


jakobbotsch Jun 26, 2026
d4603a8

Fix


jakobbotsch Jun 26, 2026
4fc43ab

Also allow TransparentAwait


jakobbotsch Jun 26, 2026
653e982

Reset tailcall prefix flag before importing RET in async version


jakobbotsch Jun 27, 2026
0d7296d

Address feedback, remove unnecessary check


jakobbotsch Jun 29, 2026

File filter

Filter by extension
Filter by extension
Conversations

Failed to load comments. 
Loading
Jump to

Jump to file


Failed to load files. 
Loading
 Diff view

 Diff view


14 changes: 13 additions & 1 deletion
src/coreclr/jit/importer.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -4602,7 +4602,8 @@ bool Compiler::impIsImplicitTailCallCandidate(
#endif // !FEATURE_TAILCALL_OPT_SHARED_RETURN

 // must be call+ret or call+pop+ret
 if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive))
 if (!impIsTailCallILPattern(false, opcode, codeAddrOfNextOpcode, codeEnd, isRecursive) &&
 ((prefixFlags & PREFIX_IS_ASYNC_VERSION_TAIL_AWAIT) == 0))
 {
 return false;
 }
Expand DownExpand Up@@ -9331,6 +9332,7 @@ void Compiler::impImportBlockCode(BasicBlock* block)
 impAppendTree(gtUnusedValNode(val), CHECK_SPILL_ALL, impCurStmtDI);
 }

 prefixFlags &= ~PREFIX_TAILCALL;
 goto RET;
 }

Expand DownExpand Up@@ -11784,6 +11786,16 @@ bool Compiler::impWrapTopOfStackInAwait()
 if (impInlineRoot()->compIsAsyncVersion())
 {
 asyncInfo->IsTailAwait = !compIsForInlining() || impInlineInfo->iciCall->GetAsyncInfo().IsTailAwait;

#if FEATURE_TAILCALL_OPT
 // We intentionally do not consult with the EE and canTailCall because
 // this is us introducing a call as an implementation detail and not a
 // user-introduced call.
 if (asyncInfo->IsTailAwait && opts.compTailCallOpt && opts.OptimizationEnabled())
 {
 awaitCall->gtCallMoreFlags |= GTF_CALL_M_IMPLICIT_TAILCALL;
 }
#endif
Comment thread
jakobbotsch marked this conversation as resolved.

 }
 else
 {
Expand Down

18 changes: 12 additions & 6 deletions
src/coreclr/jit/importercalls.cpp

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -66,7 +66,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
 // to see any imperative security.
 // Reverse P/Invokes need a call to CORINFO_HELP_JIT_REVERSE_PINVOKE_EXIT
 // at the end, so tailcalls should be disabled.
 // Async methods need to restore contexts, so tailcalls should be disabled.
 if (info.compFlags & CORINFO_FLG_SYNCH)
 {
 canTailCall = false;
Expand All@@ -77,11 +76,6 @@ var_types Compiler::impImportCall(OPCODE opcode,
 canTailCall = false;
 szCanTailCallFailReason = "Caller is Reverse P/Invoke";
 }
 else if (compIsAsync())
 {
 canTailCall = false;
 szCanTailCallFailReason = "Caller is async method";
 }
#if !FEATURE_FIXED_OUT_ARGS
 else if (info.compIsVarArgs)
 {
Expand DownExpand Up@@ -1141,6 +1135,18 @@ var_types Compiler::impImportCall(OPCODE opcode,
 BADCODE("Stack should be empty after tailcall");
 }

 // Async methods need to restore contexts, so in general tailcalls
 // should be disabled. The exception is a tail await: for those the JIT
 // directly returns the callee's continuation to the caller and no
 // context needs to be restored, so the async call can be turned into a
 // real tail call. Any other tail call candidate in an async method
 // must be disqualified.
 if (canTailCall && compIsAsync() && (!call->AsCall()->IsAsync() || !call->AsCall()->GetAsyncInfo().IsTailAwait))
 {
 canTailCall = false;
 szCanTailCallFailReason = "Caller is async method and call is not a tail await";
 }
Comment thread
jakobbotsch marked this conversation as resolved.

Comment thread
jakobbotsch marked this conversation as resolved.

Comment thread
jakobbotsch marked this conversation as resolved.


 // For opportunistic tailcalls we allow implicit widening, i.e. tailcalls from int32 -> int16, since the
 // managed calling convention dictates that the callee widens the value. For explicit tailcalls or async
 // functions we don't want to require this detail of the calling convention to bubble up to helper
Expand Down
Loading