Improve fgGetStaticFieldSeqAndAddress and fgValueNumberConstLoad#128638
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Improve fgGetStaticFieldSeqAndAddress and fgValueNumberConstLoad#128638EgorBo wants to merge 2 commits into
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Pull request overview
This PR updates JIT value-numbering helpers in valuenum.cpp to better recognize static-field address patterns (including cases where constant offsets are hidden in VNs) and to widen constant-load folding opportunities during value numbering.
Changes:
- Refactors
fgGetStaticFieldSeqAndAddressinto an instance method and enhances it to use conservative-normal VNs plusValueNumStore::PeelOffsetsto recover additional constant offsets. - Updates constant-load VN folding (
fgValueNumberConstLoad) to preserve exception sets when applying folded VNs and to attempt folding from additional address forms (including icon handles). - Adjusts some static-field content reads to pass
ignoreMovableObjects=falseand updates call sites to the newfgGetStaticFieldSeqAndAddresssignature.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
| src/coreclr/jit/valuenum.cpp | Enhances static-field address detection via conservative VNs + VN offset peeling; widens const-load VN folding and preserves exception sets when applying folded VNs. |
| src/coreclr/jit/compiler.h | Changes fgGetStaticFieldSeqAndAddress declaration to instance method and adds a new VN-based folding method declaration. |
| } | ||
| *ppValue = new (alloc) uint8_t[(size_t)size]; | ||
| return info.compCompHnd->getStaticFieldContent(fld, *ppValue, size, (int)byteOffset); | ||
| return info.compCompHnd->getStaticFieldContent(fld, *ppValue, size, (int)byteOffset, false); |
Comment on lines
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| // Pass ignoreMovableObjects=false so we can fold ref-typed static readonly fields | ||
| // even when the referenced object lives on the regular (movable) heap. The JIT-side | ||
| // handle returned by the runtime keeps the object alive for the lifetime of the | ||
| // compiled code. | ||
| if (info.compCompHnd->getStaticFieldContent(fieldHandle, buffer, size, (int)byteOffset, false)) | ||
| { |
| PhaseStatus fgVNBasedIntrinsicExpansion(); | ||
| bool fgVNBasedIntrinsicExpansionForCall(BasicBlock** pBlock, Statement* stmt, GenTreeCall* call); | ||
| bool fgVNBasedIntrinsicExpansionForCall_ReadUtf8(BasicBlock** pBlock, Statement* stmt, GenTreeCall* call); | ||
| bool fgVNBasedFoldSequenceEqualCall(BasicBlock** pBlock, Statement* stmt, GenTreeCall* call); |
The Copilot PR review caught two issues that I have confirmed by adding a local regression test (movable static readonly object reference): 1. Passing ignoreMovableObjects=false to getStaticFieldContent for a ref-typed static field returns a tagged JIT-side OBJECTHANDLE rather than the field's actual reference value. The JIT then folded that value as a plain immediate, but for non-frozen (movable) objects the GC moves the underlying object so the immediate becomes stale. Reverting both call sites to the default (ignoreMovableObjects=true) restores the safe behavior: folding only succeeds when the object is in a frozen segment. 2. Drops the orphan fgVNBasedFoldSequenceEqualCall declaration from compiler.h; no implementation/callers exist for it. Local validation: * Hand-crafted test with a static readonly object Obj = new object() and Bench.Test(o) => o == Obj returned false even when called with Bench.Obj before the fix; passes after. * SPMI replay clean on benchmarks.run, coreclr_tests, libraries.crossgen2, libraries.pmi (no asserts). * SPMI asmdiffs: no asm diffs on any of those four collections, confirming the remaining VN refactor is functionally equivalent to main. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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