JIT: forward-sub cheap address temps with multiple uses - #129312

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JIT: forward-sub cheap address temps with multiple uses#129312
AndyAyersMS merged 3 commits into
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AndyAyersMS:fix-67187-fwdsub

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@AndyAyersMSAndyAyersMS commented Jun 12, 2026

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Substitute a FIELD_ADDR chain rooted at a local at every use site so the dup-spill temp for field updates no longer blocks address-mode containment in Lowering. Also refactor the FIELD_ADDR walk into gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and impIsAddressInLocal.

Fixes#67187.

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This change was authored with the assistance of GitHub Copilot CLI.

CopilotAI review requested due to automatic review settings June 12, 2026 00:41
@github-actionsgithub-actionsBot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Jun 12, 2026
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For the canonical repro:

structFooS{publicinta,b;}classStructContainer{FooSfoo;publicvoidUpdate(){foo.a++;foo.b++;}}

x64 codegen (FullOpts), 12 bytes / 4 insns → 6 bytes / 2 insns:

; Beforelearax,[rcx+0x08]inc dword ptr [rax]addrcx,12inc dword ptr [rcx]; Afterinc dword ptr [rcx+0x08]inc dword ptr [rcx+0x0C]

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@dhartglassMSFT PTAL
fyi @dotnet/jit-contrib

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Pull request overview

This PR extends the JIT’s forward-substitution phase to allow substituting certain cheap “address temp” expressions at multiple use sites (not just a single last-use), primarily to unblock downstream address-mode containment in Lowering. It also factors out a common GT_FIELD_ADDR-peeling loop into Compiler::gtPeelFieldAddrs and reuses it from a couple of other call sites.

Changes:

  • Add Compiler::gtPeelFieldAddrs and use it from impIsAddressInLocal and fgAddrCouldBeHeap.
  • Add a multi-use forward-substitution path for “cheap reorderable address trees”, implemented via fgForwardSubMultiUse.
  • Update compiler.h with new helper/method declarations.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file
FileDescription
src/coreclr/jit/promotiondecomposition.cppAdds Compiler::gtPeelFieldAddrs helper implementation.
src/coreclr/jit/importer.cppReplaces local FIELD_ADDR peeling with gtPeelFieldAddrs.
src/coreclr/jit/forwardsub.cppAdds cheap-address detection and multi-use forward-substitution logic.
src/coreclr/jit/flowgraph.cppReuses gtPeelFieldAddrs in fgAddrCouldBeHeap.
src/coreclr/jit/compiler.hDeclares gtPeelFieldAddrs and fgForwardSubMultiUse.

Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp Outdated
Comment threadsrc/coreclr/jit/forwardsub.cpp Outdated
Comment threadsrc/coreclr/jit/importer.cpp Outdated
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Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Comment threadsrc/coreclr/jit/forwardsub.cpp Outdated
Comment threadsrc/coreclr/jit/forwardsub.cpp
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@AndyAyersMS
JIT: forward-sub cheap address temps with multiple uses
71a0a06
Substitute a FIELD_ADDR chain rooted at a local at every use site so
the dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
The multi-use path pre-allocates every clone before mutating the IR
(so a gtCloneExpr failure bails cleanly), caps the use count at four
to keep the targeted patterns in scope, and conservatively clears
GTF_VAR_DEATH bits on every LCL_VAR in the inserted copies. The peel
helper has a const overload so callers like impIsAddressInLocal stay
const-safe.
Fixesdotnet#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@pavel-purmapavel-purma mentioned this pull request Jun 12, 2026
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LGTM including removing all GTF_VAR_DEATH_MASK.

@AndyAyersMS
Address review: clarify JITDUMP wording
cbfb03a
Per @JulieLeeMSFT: the bail message also fires on > MaxUses, not just
on too few uses.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI review requested due to automatic review settings June 12, 2026 20:33
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Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
@AndyAyersMS
Address remaining review nits
7806afa
- Clarify fgIsCheapReorderableAddressTree Returns: doc to make the
zero-hop (bare LCL_VAR/LCL_ADDR) case explicit.
- Generalize the JITDUMP bail message in the multi-use call site;
fgForwardSubMultiUse can fail for multiple reasons.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@AndyAyersMS

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Helps arm64 more than I would have expected.

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/ba-g The job running on agent NetCore-Public 131 ran longer than the maximum time of 300 minutes

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AndyAyersMS merged commit 57b7935 into dotnet:mainJun 13, 2026
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@dotnet-maestrodotnet-maestroBot mentioned this pull request Jun 14, 2026
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eiriktsarpalis pushed a commit that referenced this pull request Jul 15, 2026
@AndyAyersMS@eiriktsarpalis
JIT: forward-sub cheap address temps with multiple uses (#129312)
8964ea9
Substitute a FIELD_ADDR chain rooted at a local at every use site so the
dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
Fixes#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
---------
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@github-actionsgithub-actionsBot locked and limited conversation to collaborators Jul 18, 2026
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peephole optimization for lea command

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JIT: forward-sub cheap address temps with multiple uses - #129312
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AndyAyersMS:fix-67187-fwdsub
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JIT: forward-sub cheap address temps with multiple uses#129312
AndyAyersMS merged 3 commits into
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Substitute a FIELD_ADDR chain rooted at a local at every use site so the dup-spill temp for field updates no longer blocks address-mode containment in Lowering. Also refactor the FIELD_ADDR walk into gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and impIsAddressInLocal.
Fixes#67187.
Note
This change was authored with the assistance of GitHub Copilot CLI.
CopilotAI
review requested due to automatic review settings
June 12, 2026 00:41
@github-actionsgithub-actionsBot
added
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area-CodeGen-coreclr
CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
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For the canonical repro:
structFooS{publicinta,b;}classStructContainer{FooSfoo;publicvoidUpdate(){foo.a++;foo.b++;}}
x64 codegen (FullOpts), 12 bytes / 4 insns → 6 bytes / 2 insns:
; Beforelearax,[rcx+0x08]inc dword ptr [rax]addrcx,12inc dword ptr [rcx]; Afterinc dword ptr [rcx+0x08]inc dword ptr [rcx+0x0C]
Note
This comment was authored with the assistance of GitHub Copilot CLI.
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@dhartglassMSFT PTAL

fyi @dotnet/jit-contrib
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Pull request overview
This PR extends the JIT’s forward-substitution phase to allow substituting certain cheap “address temp” expressions at multiple use sites (not just a single last-use), primarily to unblock downstream address-mode containment in Lowering. It also factors out a common GT_FIELD_ADDR-peeling loop into Compiler::gtPeelFieldAddrs and reuses it from a couple of other call sites.
Changes:
  • Add Compiler::gtPeelFieldAddrs and use it from impIsAddressInLocal and fgAddrCouldBeHeap.
  • Add a multi-use forward-substitution path for “cheap reorderable address trees”, implemented via fgForwardSubMultiUse.
  • Update compiler.h with new helper/method declarations.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
Show a summary per file
FileDescription
src/coreclr/jit/promotiondecomposition.cppAdds Compiler::gtPeelFieldAddrs helper implementation.
src/coreclr/jit/importer.cppReplaces local FIELD_ADDR peeling with gtPeelFieldAddrs.
src/coreclr/jit/forwardsub.cppAdds cheap-address detection and multi-use forward-substitution logic.
src/coreclr/jit/flowgraph.cppReuses gtPeelFieldAddrs in fgAddrCouldBeHeap.
src/coreclr/jit/compiler.hDeclares gtPeelFieldAddrs and fgForwardSubMultiUse.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
Outdated

Comment threadsrc/coreclr/jit/forwardsub.cpp
Outdated

Comment threadsrc/coreclr/jit/importer.cpp
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Outdated

Comment threadsrc/coreclr/jit/forwardsub.cpp

This was referenced Jun 12, 2026

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@AndyAyersMS
JIT: forward-sub cheap address temps with multiple uses
71a0a06
Substitute a FIELD_ADDR chain rooted at a local at every use site so
the dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
The multi-use path pre-allocates every clone before mutating the IR
(so a gtCloneExpr failure bails cleanly), caps the use count at four
to keep the targeted patterns in scope, and conservatively clears
GTF_VAR_DEATH bits on every LCL_VAR in the inserted copies. The peel
helper has a const overload so callers like impIsAddressInLocal stay
const-safe.
Fixesdotnet#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@pavel-purmapavel-purma
mentioned this pull request
Jun 12, 2026
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LGTM including removing all GTF_VAR_DEATH_MASK.
@AndyAyersMS
Address review: clarify JITDUMP wording
cbfb03a
Per @JulieLeeMSFT: the bail message also fires on > MaxUses, not just
on too few uses.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
@AndyAyersMS
Address remaining review nits
7806afa
- Clarify fgIsCheapReorderableAddressTree Returns: doc to make the
zero-hop (bare LCL_VAR/LCL_ADDR) case explicit.
- Generalize the JITDUMP bail message in the multi-use call site;
fgForwardSubMultiUse can fail for multiple reasons.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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diffs
Helps arm64 more than I would have expected.
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/ba-g The job running on agent NetCore-Public 131 ran longer than the maximum time of 300 minutes
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@AndyAyersMS@eiriktsarpalis
JIT: forward-sub cheap address temps with multiple uses (#129312)
8964ea9
Substitute a FIELD_ADDR chain rooted at a local at every use site so the
dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
Fixes#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
---------
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@github-actionsgithub-actionsBot
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peephole optimization for lea command


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JIT: forward-sub cheap address temps with multiple uses - #129312
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AndyAyersMS:fix-67187-fwdsub
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Merged
JIT: forward-sub cheap address temps with multiple uses#129312
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Substitute a FIELD_ADDR chain rooted at a local at every use site so the dup-spill temp for field updates no longer blocks address-mode containment in Lowering. Also refactor the FIELD_ADDR walk into gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and impIsAddressInLocal.
Fixes#67187.
Note
This change was authored with the assistance of GitHub Copilot CLI.
CopilotAI
review requested due to automatic review settings
June 12, 2026 00:41
@github-actionsgithub-actionsBot
added
the 
area-CodeGen-coreclr
CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
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Jun 12, 2026
@AndyAyersMS
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For the canonical repro:
structFooS{publicinta,b;}classStructContainer{FooSfoo;publicvoidUpdate(){foo.a++;foo.b++;}}
x64 codegen (FullOpts), 12 bytes / 4 insns → 6 bytes / 2 insns:
; Beforelearax,[rcx+0x08]inc dword ptr [rax]addrcx,12inc dword ptr [rcx]; Afterinc dword ptr [rcx+0x08]inc dword ptr [rcx+0x0C]
Note
This comment was authored with the assistance of GitHub Copilot CLI.
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@dhartglassMSFT PTAL

fyi @dotnet/jit-contrib
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Pull request overview
This PR extends the JIT’s forward-substitution phase to allow substituting certain cheap “address temp” expressions at multiple use sites (not just a single last-use), primarily to unblock downstream address-mode containment in Lowering. It also factors out a common GT_FIELD_ADDR-peeling loop into Compiler::gtPeelFieldAddrs and reuses it from a couple of other call sites.
Changes:
  • Add Compiler::gtPeelFieldAddrs and use it from impIsAddressInLocal and fgAddrCouldBeHeap.
  • Add a multi-use forward-substitution path for “cheap reorderable address trees”, implemented via fgForwardSubMultiUse.
  • Update compiler.h with new helper/method declarations.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
Show a summary per file
FileDescription
src/coreclr/jit/promotiondecomposition.cppAdds Compiler::gtPeelFieldAddrs helper implementation.
src/coreclr/jit/importer.cppReplaces local FIELD_ADDR peeling with gtPeelFieldAddrs.
src/coreclr/jit/forwardsub.cppAdds cheap-address detection and multi-use forward-substitution logic.
src/coreclr/jit/flowgraph.cppReuses gtPeelFieldAddrs in fgAddrCouldBeHeap.
src/coreclr/jit/compiler.hDeclares gtPeelFieldAddrs and fgForwardSubMultiUse.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
Outdated

Comment threadsrc/coreclr/jit/forwardsub.cpp
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Comment threadsrc/coreclr/jit/importer.cpp
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Outdated

Comment threadsrc/coreclr/jit/forwardsub.cpp

This was referenced Jun 12, 2026

Closed


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 Closed

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 Closed

 Closed

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@AndyAyersMS
JIT: forward-sub cheap address temps with multiple uses
71a0a06
Substitute a FIELD_ADDR chain rooted at a local at every use site so
the dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
The multi-use path pre-allocates every clone before mutating the IR
(so a gtCloneExpr failure bails cleanly), caps the use count at four
to keep the targeted patterns in scope, and conservatively clears
GTF_VAR_DEATH bits on every LCL_VAR in the inserted copies. The peel
helper has a const overload so callers like impIsAddressInLocal stay
const-safe.
Fixesdotnet#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@pavel-purmapavel-purma
mentioned this pull request
Jun 12, 2026
 Closed


This was referenced Jun 12, 2026
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JulieLeeMSFT
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LGTM including removing all GTF_VAR_DEATH_MASK.
@AndyAyersMS
Address review: clarify JITDUMP wording
cbfb03a
Per @JulieLeeMSFT: the bail message also fires on > MaxUses, not just
on too few uses.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
@AndyAyersMS
Address remaining review nits
7806afa
- Clarify fgIsCheapReorderableAddressTree Returns: doc to make the
zero-hop (bare LCL_VAR/LCL_ADDR) case explicit.
- Generalize the JITDUMP bail message in the multi-use call site;
fgForwardSubMultiUse can fail for multiple reasons.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Helps arm64 more than I would have expected.
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/ba-g The job running on agent NetCore-Public 131 ran longer than the maximum time of 300 minutes
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JIT: forward-sub cheap address temps with multiple uses (#129312)
8964ea9
Substitute a FIELD_ADDR chain rooted at a local at every use site so the
dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
Fixes#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
---------
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JIT: forward-sub cheap address temps with multiple uses - #129312
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Substitute a FIELD_ADDR chain rooted at a local at every use site so the dup-spill temp for field updates no longer blocks address-mode containment in Lowering. Also refactor the FIELD_ADDR walk into gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and impIsAddressInLocal.
Fixes#67187.
Note
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For the canonical repro:
structFooS{publicinta,b;}classStructContainer{FooSfoo;publicvoidUpdate(){foo.a++;foo.b++;}}
x64 codegen (FullOpts), 12 bytes / 4 insns → 6 bytes / 2 insns:
; Beforelearax,[rcx+0x08]inc dword ptr [rax]addrcx,12inc dword ptr [rcx]; Afterinc dword ptr [rcx+0x08]inc dword ptr [rcx+0x0C]
Note
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@dhartglassMSFT PTAL

fyi @dotnet/jit-contrib
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Pull request overview
This PR extends the JIT’s forward-substitution phase to allow substituting certain cheap “address temp” expressions at multiple use sites (not just a single last-use), primarily to unblock downstream address-mode containment in Lowering. It also factors out a common GT_FIELD_ADDR-peeling loop into Compiler::gtPeelFieldAddrs and reuses it from a couple of other call sites.
Changes:
  • Add Compiler::gtPeelFieldAddrs and use it from impIsAddressInLocal and fgAddrCouldBeHeap.
  • Add a multi-use forward-substitution path for “cheap reorderable address trees”, implemented via fgForwardSubMultiUse.
  • Update compiler.h with new helper/method declarations.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
Show a summary per file
FileDescription
src/coreclr/jit/promotiondecomposition.cppAdds Compiler::gtPeelFieldAddrs helper implementation.
src/coreclr/jit/importer.cppReplaces local FIELD_ADDR peeling with gtPeelFieldAddrs.
src/coreclr/jit/forwardsub.cppAdds cheap-address detection and multi-use forward-substitution logic.
src/coreclr/jit/flowgraph.cppReuses gtPeelFieldAddrs in fgAddrCouldBeHeap.
src/coreclr/jit/compiler.hDeclares gtPeelFieldAddrs and fgForwardSubMultiUse.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
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Comment threadsrc/coreclr/jit/forwardsub.cpp
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Comment threadsrc/coreclr/jit/importer.cpp
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Comment threadsrc/coreclr/jit/forwardsub.cpp
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Comment threadsrc/coreclr/jit/forwardsub.cpp

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@AndyAyersMS
JIT: forward-sub cheap address temps with multiple uses
71a0a06
Substitute a FIELD_ADDR chain rooted at a local at every use site so
the dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
The multi-use path pre-allocates every clone before mutating the IR
(so a gtCloneExpr failure bails cleanly), caps the use count at four
to keep the targeted patterns in scope, and conservatively clears
GTF_VAR_DEATH bits on every LCL_VAR in the inserted copies. The peel
helper has a const overload so callers like impIsAddressInLocal stay
const-safe.
Fixesdotnet#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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LGTM including removing all GTF_VAR_DEATH_MASK.
@AndyAyersMS
Address review: clarify JITDUMP wording
cbfb03a
Per @JulieLeeMSFT: the bail message also fires on > MaxUses, not just
on too few uses.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
@AndyAyersMS
Address remaining review nits
7806afa
- Clarify fgIsCheapReorderableAddressTree Returns: doc to make the
zero-hop (bare LCL_VAR/LCL_ADDR) case explicit.
- Generalize the JITDUMP bail message in the multi-use call site;
fgForwardSubMultiUse can fail for multiple reasons.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Helps arm64 more than I would have expected.
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This was referenced Jun 13, 2026

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/ba-g The job running on agent NetCore-Public 131 ran longer than the maximum time of 300 minutes
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merged commit 57b7935
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132 of 139 checks passed

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eiriktsarpalis pushed a commit
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@AndyAyersMS@eiriktsarpalis
JIT: forward-sub cheap address temps with multiple uses (#129312)
8964ea9
Substitute a FIELD_ADDR chain rooted at a local at every use site so the
dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
Fixes#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
---------
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@github-actionsgithub-actionsBot
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peephole optimization for lea command


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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);
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trackingParams.forEach(function(p) {
if (u.searchParams.has(p)) {
u.searchParams.delete(p);
changed = true;
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})();
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JIT: forward-sub cheap address temps with multiple uses - #129312
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JIT: forward-sub cheap address temps with multiple uses#129312
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Substitute a FIELD_ADDR chain rooted at a local at every use site so the dup-spill temp for field updates no longer blocks address-mode containment in Lowering. Also refactor the FIELD_ADDR walk into gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and impIsAddressInLocal.
Fixes#67187.
Note
This change was authored with the assistance of GitHub Copilot CLI.
CopilotAI
review requested due to automatic review settings
June 12, 2026 00:41
@github-actionsgithub-actionsBot
added
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For the canonical repro:
structFooS{publicinta,b;}classStructContainer{FooSfoo;publicvoidUpdate(){foo.a++;foo.b++;}}
x64 codegen (FullOpts), 12 bytes / 4 insns → 6 bytes / 2 insns:
; Beforelearax,[rcx+0x08]inc dword ptr [rax]addrcx,12inc dword ptr [rcx]; Afterinc dword ptr [rcx+0x08]inc dword ptr [rcx+0x0C]
Note
This comment was authored with the assistance of GitHub Copilot CLI.
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@dhartglassMSFT PTAL

fyi @dotnet/jit-contrib
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Pull request overview
This PR extends the JIT’s forward-substitution phase to allow substituting certain cheap “address temp” expressions at multiple use sites (not just a single last-use), primarily to unblock downstream address-mode containment in Lowering. It also factors out a common GT_FIELD_ADDR-peeling loop into Compiler::gtPeelFieldAddrs and reuses it from a couple of other call sites.
Changes:
  • Add Compiler::gtPeelFieldAddrs and use it from impIsAddressInLocal and fgAddrCouldBeHeap.
  • Add a multi-use forward-substitution path for “cheap reorderable address trees”, implemented via fgForwardSubMultiUse.
  • Update compiler.h with new helper/method declarations.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
Show a summary per file
FileDescription
src/coreclr/jit/promotiondecomposition.cppAdds Compiler::gtPeelFieldAddrs helper implementation.
src/coreclr/jit/importer.cppReplaces local FIELD_ADDR peeling with gtPeelFieldAddrs.
src/coreclr/jit/forwardsub.cppAdds cheap-address detection and multi-use forward-substitution logic.
src/coreclr/jit/flowgraph.cppReuses gtPeelFieldAddrs in fgAddrCouldBeHeap.
src/coreclr/jit/compiler.hDeclares gtPeelFieldAddrs and fgForwardSubMultiUse.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
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Comment threadsrc/coreclr/jit/forwardsub.cpp
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Comment threadsrc/coreclr/jit/importer.cpp
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Comment threadsrc/coreclr/jit/forwardsub.cpp
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Comment threadsrc/coreclr/jit/forwardsub.cpp

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@AndyAyersMS
JIT: forward-sub cheap address temps with multiple uses
71a0a06
Substitute a FIELD_ADDR chain rooted at a local at every use site so
the dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
The multi-use path pre-allocates every clone before mutating the IR
(so a gtCloneExpr failure bails cleanly), caps the use count at four
to keep the targeted patterns in scope, and conservatively clears
GTF_VAR_DEATH bits on every LCL_VAR in the inserted copies. The peel
helper has a const overload so callers like impIsAddressInLocal stay
const-safe.
Fixesdotnet#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@pavel-purmapavel-purma
mentioned this pull request
Jun 12, 2026
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LGTM including removing all GTF_VAR_DEATH_MASK.
@AndyAyersMS
Address review: clarify JITDUMP wording
cbfb03a
Per @JulieLeeMSFT: the bail message also fires on > MaxUses, not just
on too few uses.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
@AndyAyersMS
Address remaining review nits
7806afa
- Clarify fgIsCheapReorderableAddressTree Returns: doc to make the
zero-hop (bare LCL_VAR/LCL_ADDR) case explicit.
- Generalize the JITDUMP bail message in the multi-use call site;
fgForwardSubMultiUse can fail for multiple reasons.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Helps arm64 more than I would have expected.
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enabled auto-merge (squash)
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This was referenced Jun 13, 2026

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/ba-g The job running on agent NetCore-Public 131 ran longer than the maximum time of 300 minutes
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132 of 139 checks passed

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eiriktsarpalis pushed a commit
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@AndyAyersMS@eiriktsarpalis
JIT: forward-sub cheap address temps with multiple uses (#129312)
8964ea9
Substitute a FIELD_ADDR chain rooted at a local at every use site so the
dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
Fixes#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
---------
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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peephole optimization for lea command


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JIT: forward-sub cheap address temps with multiple uses - #129312
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JIT: forward-sub cheap address temps with multiple uses#129312
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Substitute a FIELD_ADDR chain rooted at a local at every use site so the dup-spill temp for field updates no longer blocks address-mode containment in Lowering. Also refactor the FIELD_ADDR walk into gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and impIsAddressInLocal.
Fixes#67187.
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For the canonical repro:
structFooS{publicinta,b;}classStructContainer{FooSfoo;publicvoidUpdate(){foo.a++;foo.b++;}}
x64 codegen (FullOpts), 12 bytes / 4 insns → 6 bytes / 2 insns:
; Beforelearax,[rcx+0x08]inc dword ptr [rax]addrcx,12inc dword ptr [rcx]; Afterinc dword ptr [rcx+0x08]inc dword ptr [rcx+0x0C]
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@dhartglassMSFT PTAL

fyi @dotnet/jit-contrib
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Pull request overview
This PR extends the JIT’s forward-substitution phase to allow substituting certain cheap “address temp” expressions at multiple use sites (not just a single last-use), primarily to unblock downstream address-mode containment in Lowering. It also factors out a common GT_FIELD_ADDR-peeling loop into Compiler::gtPeelFieldAddrs and reuses it from a couple of other call sites.
Changes:
  • Add Compiler::gtPeelFieldAddrs and use it from impIsAddressInLocal and fgAddrCouldBeHeap.
  • Add a multi-use forward-substitution path for “cheap reorderable address trees”, implemented via fgForwardSubMultiUse.
  • Update compiler.h with new helper/method declarations.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
Show a summary per file
FileDescription
src/coreclr/jit/promotiondecomposition.cppAdds Compiler::gtPeelFieldAddrs helper implementation.
src/coreclr/jit/importer.cppReplaces local FIELD_ADDR peeling with gtPeelFieldAddrs.
src/coreclr/jit/forwardsub.cppAdds cheap-address detection and multi-use forward-substitution logic.
src/coreclr/jit/flowgraph.cppReuses gtPeelFieldAddrs in fgAddrCouldBeHeap.
src/coreclr/jit/compiler.hDeclares gtPeelFieldAddrs and fgForwardSubMultiUse.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
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Comment threadsrc/coreclr/jit/forwardsub.cpp
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Comment threadsrc/coreclr/jit/importer.cpp
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Comment threadsrc/coreclr/jit/forwardsub.cpp
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@AndyAyersMS
JIT: forward-sub cheap address temps with multiple uses
71a0a06
Substitute a FIELD_ADDR chain rooted at a local at every use site so
the dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
The multi-use path pre-allocates every clone before mutating the IR
(so a gtCloneExpr failure bails cleanly), caps the use count at four
to keep the targeted patterns in scope, and conservatively clears
GTF_VAR_DEATH bits on every LCL_VAR in the inserted copies. The peel
helper has a const overload so callers like impIsAddressInLocal stay
const-safe.
Fixesdotnet#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@pavel-purmapavel-purma
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LGTM including removing all GTF_VAR_DEATH_MASK.
@AndyAyersMS
Address review: clarify JITDUMP wording
cbfb03a
Per @JulieLeeMSFT: the bail message also fires on > MaxUses, not just
on too few uses.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
@AndyAyersMS
Address remaining review nits
7806afa
- Clarify fgIsCheapReorderableAddressTree Returns: doc to make the
zero-hop (bare LCL_VAR/LCL_ADDR) case explicit.
- Generalize the JITDUMP bail message in the multi-use call site;
fgForwardSubMultiUse can fail for multiple reasons.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Helps arm64 more than I would have expected.
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/ba-g The job running on agent NetCore-Public 131 ran longer than the maximum time of 300 minutes
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@AndyAyersMS@eiriktsarpalis
JIT: forward-sub cheap address temps with multiple uses (#129312)
8964ea9
Substitute a FIELD_ADDR chain rooted at a local at every use site so the
dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
Fixes#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
---------
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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peephole optimization for lea command


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JIT: forward-sub cheap address temps with multiple uses - #129312
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AndyAyersMS:fix-67187-fwdsub
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Merged
JIT: forward-sub cheap address temps with multiple uses#129312
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Substitute a FIELD_ADDR chain rooted at a local at every use site so the dup-spill temp for field updates no longer blocks address-mode containment in Lowering. Also refactor the FIELD_ADDR walk into gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and impIsAddressInLocal.
Fixes#67187.
Note
This change was authored with the assistance of GitHub Copilot CLI.
CopilotAI
review requested due to automatic review settings
June 12, 2026 00:41
@github-actionsgithub-actionsBot
added
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area-CodeGen-coreclr
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For the canonical repro:
structFooS{publicinta,b;}classStructContainer{FooSfoo;publicvoidUpdate(){foo.a++;foo.b++;}}
x64 codegen (FullOpts), 12 bytes / 4 insns → 6 bytes / 2 insns:
; Beforelearax,[rcx+0x08]inc dword ptr [rax]addrcx,12inc dword ptr [rcx]; Afterinc dword ptr [rcx+0x08]inc dword ptr [rcx+0x0C]
Note
This comment was authored with the assistance of GitHub Copilot CLI.
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@dhartglassMSFT PTAL

fyi @dotnet/jit-contrib
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Pull request overview
This PR extends the JIT’s forward-substitution phase to allow substituting certain cheap “address temp” expressions at multiple use sites (not just a single last-use), primarily to unblock downstream address-mode containment in Lowering. It also factors out a common GT_FIELD_ADDR-peeling loop into Compiler::gtPeelFieldAddrs and reuses it from a couple of other call sites.
Changes:
  • Add Compiler::gtPeelFieldAddrs and use it from impIsAddressInLocal and fgAddrCouldBeHeap.
  • Add a multi-use forward-substitution path for “cheap reorderable address trees”, implemented via fgForwardSubMultiUse.
  • Update compiler.h with new helper/method declarations.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
Show a summary per file
FileDescription
src/coreclr/jit/promotiondecomposition.cppAdds Compiler::gtPeelFieldAddrs helper implementation.
src/coreclr/jit/importer.cppReplaces local FIELD_ADDR peeling with gtPeelFieldAddrs.
src/coreclr/jit/forwardsub.cppAdds cheap-address detection and multi-use forward-substitution logic.
src/coreclr/jit/flowgraph.cppReuses gtPeelFieldAddrs in fgAddrCouldBeHeap.
src/coreclr/jit/compiler.hDeclares gtPeelFieldAddrs and fgForwardSubMultiUse.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
Outdated

Comment threadsrc/coreclr/jit/forwardsub.cpp
Outdated

Comment threadsrc/coreclr/jit/importer.cpp
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Outdated

Comment threadsrc/coreclr/jit/forwardsub.cpp

This was referenced Jun 12, 2026

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 Closed

 Closed

 Closed

 Closed

 Closed

 Closed

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@AndyAyersMS
JIT: forward-sub cheap address temps with multiple uses
71a0a06
Substitute a FIELD_ADDR chain rooted at a local at every use site so
the dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
The multi-use path pre-allocates every clone before mutating the IR
(so a gtCloneExpr failure bails cleanly), caps the use count at four
to keep the targeted patterns in scope, and conservatively clears
GTF_VAR_DEATH bits on every LCL_VAR in the inserted copies. The peel
helper has a const overload so callers like impIsAddressInLocal stay
const-safe.
Fixesdotnet#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@pavel-purmapavel-purma
mentioned this pull request
Jun 12, 2026
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LGTM including removing all GTF_VAR_DEATH_MASK.
@AndyAyersMS
Address review: clarify JITDUMP wording
cbfb03a
Per @JulieLeeMSFT: the bail message also fires on > MaxUses, not just
on too few uses.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
@AndyAyersMS
Address remaining review nits
7806afa
- Clarify fgIsCheapReorderableAddressTree Returns: doc to make the
zero-hop (bare LCL_VAR/LCL_ADDR) case explicit.
- Generalize the JITDUMP bail message in the multi-use call site;
fgForwardSubMultiUse can fail for multiple reasons.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Helps arm64 more than I would have expected.
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/ba-g The job running on agent NetCore-Public 131 ran longer than the maximum time of 300 minutes
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merged commit 57b7935
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132 of 139 checks passed

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eiriktsarpalis pushed a commit
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@AndyAyersMS@eiriktsarpalis
JIT: forward-sub cheap address temps with multiple uses (#129312)
8964ea9
Substitute a FIELD_ADDR chain rooted at a local at every use site so the
dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
Fixes#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
---------
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@github-actionsgithub-actionsBot
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peephole optimization for lea command


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filter: invert(1) hue-rotate(180deg) !important;
background: #1a1a2e !important;
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/* Restore images, videos, iframes, canvas */
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.modal, .popup, .dropdown-menu, .tooltip, .popover {
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}
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::-webkit-scrollbar { background: #1a1a2e !important; }
::-webkit-scrollbar-thumb { background: #444 !important; }
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/* Selection */
::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
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JIT: forward-sub cheap address temps with multiple uses - #129312
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Substitute a FIELD_ADDR chain rooted at a local at every use site so the dup-spill temp for field updates no longer blocks address-mode containment in Lowering. Also refactor the FIELD_ADDR walk into gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and impIsAddressInLocal.
Fixes#67187.
Note
This change was authored with the assistance of GitHub Copilot CLI.
CopilotAI
review requested due to automatic review settings
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@github-actionsgithub-actionsBot
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For the canonical repro:
structFooS{publicinta,b;}classStructContainer{FooSfoo;publicvoidUpdate(){foo.a++;foo.b++;}}
x64 codegen (FullOpts), 12 bytes / 4 insns → 6 bytes / 2 insns:
; Beforelearax,[rcx+0x08]inc dword ptr [rax]addrcx,12inc dword ptr [rcx]; Afterinc dword ptr [rcx+0x08]inc dword ptr [rcx+0x0C]
Note
This comment was authored with the assistance of GitHub Copilot CLI.
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@dhartglassMSFT PTAL

fyi @dotnet/jit-contrib
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Pull request overview
This PR extends the JIT’s forward-substitution phase to allow substituting certain cheap “address temp” expressions at multiple use sites (not just a single last-use), primarily to unblock downstream address-mode containment in Lowering. It also factors out a common GT_FIELD_ADDR-peeling loop into Compiler::gtPeelFieldAddrs and reuses it from a couple of other call sites.
Changes:
  • Add Compiler::gtPeelFieldAddrs and use it from impIsAddressInLocal and fgAddrCouldBeHeap.
  • Add a multi-use forward-substitution path for “cheap reorderable address trees”, implemented via fgForwardSubMultiUse.
  • Update compiler.h with new helper/method declarations.
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Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
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FileDescription
src/coreclr/jit/promotiondecomposition.cppAdds Compiler::gtPeelFieldAddrs helper implementation.
src/coreclr/jit/importer.cppReplaces local FIELD_ADDR peeling with gtPeelFieldAddrs.
src/coreclr/jit/forwardsub.cppAdds cheap-address detection and multi-use forward-substitution logic.
src/coreclr/jit/flowgraph.cppReuses gtPeelFieldAddrs in fgAddrCouldBeHeap.
src/coreclr/jit/compiler.hDeclares gtPeelFieldAddrs and fgForwardSubMultiUse.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
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Comment threadsrc/coreclr/jit/forwardsub.cpp
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Comment threadsrc/coreclr/jit/importer.cpp
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Comment threadsrc/coreclr/jit/forwardsub.cpp
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@AndyAyersMS
JIT: forward-sub cheap address temps with multiple uses
71a0a06
Substitute a FIELD_ADDR chain rooted at a local at every use site so
the dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
The multi-use path pre-allocates every clone before mutating the IR
(so a gtCloneExpr failure bails cleanly), caps the use count at four
to keep the targeted patterns in scope, and conservatively clears
GTF_VAR_DEATH bits on every LCL_VAR in the inserted copies. The peel
helper has a const overload so callers like impIsAddressInLocal stay
const-safe.
Fixesdotnet#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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JulieLeeMSFT
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LGTM including removing all GTF_VAR_DEATH_MASK.
@AndyAyersMS
Address review: clarify JITDUMP wording
cbfb03a
Per @JulieLeeMSFT: the bail message also fires on > MaxUses, not just
on too few uses.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Comment threadsrc/coreclr/jit/forwardsub.cpp
Comment threadsrc/coreclr/jit/forwardsub.cpp
@AndyAyersMS
Address remaining review nits
7806afa
- Clarify fgIsCheapReorderableAddressTree Returns: doc to make the
zero-hop (bare LCL_VAR/LCL_ADDR) case explicit.
- Generalize the JITDUMP bail message in the multi-use call site;
fgForwardSubMultiUse can fail for multiple reasons.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Helps arm64 more than I would have expected.
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/ba-g The job running on agent NetCore-Public 131 ran longer than the maximum time of 300 minutes
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@AndyAyersMS@eiriktsarpalis
JIT: forward-sub cheap address temps with multiple uses (#129312)
8964ea9
Substitute a FIELD_ADDR chain rooted at a local at every use site so the
dup-spill temp for field updates no longer blocks address-mode
containment in Lowering. Also refactor the FIELD_ADDR walk into
gtPeelFieldAddrs and share it with fgAddrCouldBeHeap and
impIsAddressInLocal.
Fixes#67187.
> [!NOTE]
> This change was authored with the assistance of GitHub Copilot CLI.
---------
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI

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peephole optimization for lea command


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