Stackalloc localloc conditional2 by AndyAyersMS · Pull Request #127980 · dotnet/runtime

AndyAyersMS · 2026-05-08T23:54:45Z

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…locLocalloc

…onditional2 # Conflicts: # src/coreclr/jit/codegenarm.cpp # src/coreclr/jit/codegenarm64.cpp # src/coreclr/jit/codegenloongarch64.cpp # src/coreclr/jit/codegenriscv64.cpp # src/coreclr/jit/codegenxarch.cpp # src/coreclr/jit/gentree.cpp # src/coreclr/jit/gentree.h # src/coreclr/jit/jitconfigvalues.h # src/coreclr/jit/lsraarm.cpp # src/coreclr/jit/lsraarm64.cpp # src/coreclr/jit/lsraloongarch64.cpp # src/coreclr/jit/lsrariscv64.cpp # src/coreclr/jit/lsraxarch.cpp # src/coreclr/jit/morph.cpp # src/coreclr/jit/objectalloc.cpp # src/coreclr/jit/objectalloc.h

The merge of upstream/main into StackallocLocallocConditional2 left the body of MorphNewArrNodeIntoStackAlloc in HEAD's old form (taking GenTree* len) while the header was updated to main's new signature (unsigned length, unsigned blockSize, returning unsigned int). Replace the body's signature and preamble with main's version; the rest of the function (including the return lclNum already added during the merge) is unchanged. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The five other codegen backends (xarch, arm, arm64, loongarch64, riscv64) zero LCLHEAP allocations when either info.compInitMem is set or the GTF_LCLHEAP_MUSTINIT flag is present on the LCLHEAP node. The wasm backend was missing the flag check, so an LCLHEAP marked MUSTINIT (e.g. the runtime length stack-array path that flows through helperexpansion.cpp) would not be zeroed when compInitMem is false. Validated by building clr.wasmjit subset. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Introduce an inline helper on Compiler that returns true iff a given LCLHEAP node must zero its allocation, encapsulating the common 'info.compInitMem || (tree->gtFlags & GTF_LCLHEAP_MUSTINIT)' check used by every codegen and LSRA backend. Replace the 12 inlined occurrences across xarch, arm, arm64, loongarch64, riscv64, and wasm with calls to the helper. Validated by building clr.jit and clr.wasmjit subsets. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

dotnet-policy-service · 2026-05-08T23:56:32Z

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Copilot

Pull request overview

This PR extends CoreCLR JIT object stack allocation for newarr to support cases where the array length isn’t a compile-time constant by routing allocation through a localloc-based expansion (with a runtime size check that can fall back to heap allocation). It also adds plumbing to ensure such locallocs are zero-initialized even when the method doesn’t have init-mem semantics.

Changes:

Add an objectalloc “localloc” path for stack-allocated arrays with non-constant (and optionally in-loop) lengths, controlled by new JIT config switches.
Teach stack-array helper expansion to generate a runtime size computation + conditional localloc vs heapalloc split, using a new well-known arg for element size.
Introduce GTF_LCLHEAP_MUSTINIT and propagate “must zero” semantics through LSRA and codegen via Compiler::gtMustZeroLocalloc.

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/coreclr/jit/objectalloc.h	Adds state/config fields and a localloc morph helper declaration; extends stack-allocation eligibility API with `lengthKnown`.
src/coreclr/jit/objectalloc.cpp	Implements localloc morphing for runtime-sized (and in-loop) `newarr`, and adds an eligibility guard for runtime-sized arrays with GC elements.
src/coreclr/jit/morph.cpp	Adds display support for new `WellKnownArg::StackArrayElemSize`.
src/coreclr/jit/lsraxarch.cpp	Updates LCLHEAP reg/zero-init decisions to use `gtMustZeroLocalloc` / `GTF_LCLHEAP_MUSTINIT`.
src/coreclr/jit/lsrariscv64.cpp	Switches localloc “needs init” checks to `gtMustZeroLocalloc`.
src/coreclr/jit/lsraloongarch64.cpp	Switches localloc “needs init” checks to `gtMustZeroLocalloc`.
src/coreclr/jit/lsraarm64.cpp	Switches localloc “needs init” checks to `gtMustZeroLocalloc`.
src/coreclr/jit/lsraarm.cpp	Switches localloc “needs init” checks to `gtMustZeroLocalloc`.
src/coreclr/jit/jitmetadatalist.h	Adds a new JIT metric counter for localloc-allocated arrays.
src/coreclr/jit/jitconfigvalues.h	Adds config knobs for enabling localloc-based stack array allocation and permitting it in loops.
src/coreclr/jit/helperexpansion.cpp	Implements runtime-sized stack array expansion into size-check + localloc/heapalloc CFG split, and header initialization for localloc case.
src/coreclr/jit/gentree.h	Adds `GTF_LCLHEAP_MUSTINIT` and `WellKnownArg::StackArrayElemSize`.
src/coreclr/jit/gentree.cpp	Adds formatting for the new well-known arg in arg debug messages.
src/coreclr/jit/compiler.h	Adds `Compiler::gtMustZeroLocalloc` helper to centralize localloc zero-init requirements.
src/coreclr/jit/codegenxarch.cpp	Uses `gtMustZeroLocalloc` in localloc codegen, and records localloc usage.
src/coreclr/jit/codegenwasm.cpp	Uses `gtMustZeroLocalloc` in localloc codegen.
src/coreclr/jit/codegenriscv64.cpp	Uses `gtMustZeroLocalloc` in localloc codegen.
src/coreclr/jit/codegenloongarch64.cpp	Uses `gtMustZeroLocalloc` in localloc codegen.
src/coreclr/jit/codegenarm64.cpp	Uses `gtMustZeroLocalloc` in localloc codegen.
src/coreclr/jit/codegenarm.cpp	Uses `gtMustZeroLocalloc` in localloc codegen.
src/coreclr/jit/codegen.h	Adds a `genLocallocUsed` flag to CodeGen state.

basicBlockHasBackwardJump and basicBlockInHandler in MorphAllocObjNodes are no longer used after the morph loop body was refactored into MorphAllocObjNodeHelperArr (which queries the block flags directly). MSVC tolerates this via /wd4189; clang/gcc on Linux/Mac warn. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The pointer-size round-up in fgExpandStackArrayAllocation was using (size + TARGET_POINTER_SIZE) & ~(TARGET_POINTER_SIZE - 1) which over-allocates by one pointer when the size is already aligned, and can push already-aligned sizes over the runtime stack threshold. The standard align-up formula is (size + TPS - 1) & ~(TPS - 1). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 33 out of 33 changed files in this pull request and generated 2 comments.

+            GenTree* const   zeroInit     = gtNewStoreLclVarNode(frameRunningTotalLclNum, gtNewIconNode(0, TYP_I_IMPL));
+            Statement* const zeroInitStmt = fgNewStmtFromTree(zeroInit);
+            fgInsertStmtAtBeg(fgFirstBB, zeroInitStmt);


    if (size->isContainedIntOrIImmed())
    {
        // The size node being a contained constant means that Lower has taken care of
        // zeroing the memory if compInitMem is true.
-        needsZeroing = false;
+        initMem = false;


Keep conditional localloc locals possibly heap-pointing so heap fallback references remain GC-reportable, and avoid platform-specific allocation-kind assertions outside Windows. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…ditional2-local # Conflicts: # src/coreclr/inc/jiteeversionguid.h

Copilot

Pull request overview

Copilot reviewed 33 out of 33 changed files in this pull request and generated 1 comment.

Preserve MUSTINIT zeroing for arm64 contained locallocs, update frame-running-total statement side effects, and keep conditional localloc heap-fallback locals from being treated as definitely stack-only. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Ensure in-loop stack allocation candidates embedded in uses are split and expanded through the conditional localloc helper instead of being skipped. Recompute split CFG weights so checked profile validation stays consistent. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Handle embedded conditional localloc uses by introducing a result temp when the newarr is not already stored at the statement root. Keep native-int subtraction results typed as native ints when propagating byref types, and keep GC-element arrays out of conditional localloc because their GC slots cannot be reported from variable localloc storage. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 33 out of 33 changed files in this pull request and generated 2 comments.

Stop scanning a block after conditional localloc expansion moves the current statement into new CFG blocks. Continue scanning after fixed stack-array expansions so their pseudo arguments are expanded before lowering. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Keep conditional localloc replacements typed as byrefs and materialize the x86 align8 adjusted address before replacement. Also avoid continuing the current block statement scan after a localloc expansion moves the statement to new CFG blocks. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 33 out of 33 changed files in this pull request and generated 4 comments.

+  <PropertyGroup>
+    <!-- Needed for CLRTestEnvironmentVariable -->
+    <RequiresProcessIsolation>true</RequiresProcessIsolation>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+    <JitOptimizationSensitive>true</JitOptimizationSensitive>
+  </PropertyGroup>


+    [ActiveIssue("needs triage", TestRuntimes.Mono)]
+    [Fact]
+    public static int TestNegative() => CallTestAndVerifyAllocation(VariableLengthNegative, 0, AllocationKind.Undefined, throws: true);
+


+    [ActiveIssue("needs triage", TestRuntimes.Mono)]
+    [Fact]
+    public static int TestIntMin() => CallTestAndVerifyAllocation(VariableLengthIntMin, 0, AllocationKind.Undefined, throws: true);
+


+    [ActiveIssue("needs triage", TestRuntimes.Mono)]
+    [Fact]
+    public static int TestHuge() => CallTestAndVerifyAllocation(VariableLengthHuge, 0, AllocationKind.Undefined, throws: true);


…onditional2-local

AndyAyersMS and others added 22 commits February 4, 2025 17:04

proof of concept

c5cefd3

fix flags

4d9f1bc

enable by default (for now)

e3c4019

enable for array allocations in loops too

23b4261

add missing bit of code

d096d63

add handler check; fix elem size type

032f724

fix zero init logic

1e088c4

merge main

d572dec

update post merge, cleanup a bit

526ba2f

pad localloc array size as if it was on heap; handle align8

9e7cf8e

don't allow localloc for gc type arrays

e247123

Merge branch 'main' into StackallocLocalloc

f858501

simple runtime check for stack alloc vs heap alloc

f421343

make new call instead of trying to hack up the old one

45f648e

Merge branch 'main' into StackallocLocalloc

66a8ddd

Merge remote-tracking branch 'origin/StackallocLocalloc' into Stackal…

39294f4

…locLocalloc

temp fix for linux x64 issue with misaligned frame

5540b26

Merge branch 'StackallocLocalloc' into StackallocLocallocConditional2

d7ac700

Copilot AI review requested due to automatic review settings May 8, 2026 23:54

Copilot started reviewing on behalf of AndyAyersMS May 8, 2026 23:55 View session

github-actions Bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label May 8, 2026

dotnet-policy-service Bot assigned AndyAyersMS May 8, 2026

Copilot AI reviewed May 9, 2026

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Comment thread src/coreclr/jit/objectalloc.cpp Outdated

Comment thread src/coreclr/jit/objectalloc.cpp

Comment thread src/coreclr/jit/objectalloc.cpp

Comment thread src/coreclr/jit/helperexpansion.cpp

Comment thread src/coreclr/jit/helperexpansion.cpp Outdated

AndyAyersMS and others added 2 commits May 8, 2026 19:31

build-analysis Bot mentioned this pull request Jun 27, 2026

Flaky timeout in CreateFileChangeToken_RootDeletedAndRecreated_TokenFiresWhenFileCreated #129691

Open

Copilot AI review requested due to automatic review settings June 27, 2026 02:14

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build-analysis Bot mentioned this pull request Jun 27, 2026

Multiple Helix work items fail on maccatalyst/tvos CoreCLR Release #126460

Open

AndyAyersMS and others added 2 commits June 28, 2026 08:21

Merge remote-tracking branch 'origin/main' into StackallocLocallocCon…

3e1e064

…ditional2-local # Conflicts: # src/coreclr/inc/jiteeversionguid.h

Copilot AI review requested due to automatic review settings June 29, 2026 15:15

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Comment thread src/coreclr/jit/codegenarm64.cpp

AndyAyersMS and others added 4 commits June 30, 2026 10:09

Merge origin/main into conditional localloc branch

b78e2e2

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings July 1, 2026 15:50

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Comment thread src/coreclr/jit/helperexpansion.cpp

Comment thread src/coreclr/jit/objectalloc.cpp

AndyAyersMS and others added 2 commits July 1, 2026 12:37

Copilot AI review requested due to automatic review settings July 1, 2026 23:10

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This was referenced Jul 2, 2026

System.Threading.Tasks.Tests.AsyncProfilerTests.StateMachineAsync_CallstackStressWithVaryingDepths test failure #129871

Open

[ci-scan] Test failure: AsyncProfilerTests.StateMachineAsync_CallstackStressWithVaryingDepths under libraries-jitstress #129938

Open

Merge remote-tracking branch 'upstream/main' into StackallocLocallocC…

2a86206

…onditional2-local

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