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Fix incorrect CoercedConstantValue usage in IsVNIntegralConstant - #128770
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Co-authored-by: EgorBo <[email protected]>
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[WIP] Fix incorrect CoercedConstantValue<ssize_t> usages
Fix incorrect CoercedConstantValue usage in IsVNIntegralConstant
May 29, 2026
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Pull request overview
This PR fixes IsVNIntegralConstant so JIT value-number constants are checked for integral fit after preserving the full 64-bit value, avoiding 32-bit host truncation of TYP_LONG constants.
Changes:
- Reads VN integral constants as
int64_tbefore applyingFitsIn<T>. - Preserves existing behavior for
TYP_INTwhile correctly rejecting oversizedTYP_LONGvalues.
This was referenced May 30, 2026
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LGTM.
I think the same issue might exist for ConstantValue<T>, looking at the flow
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Pull request overview
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src/coreclr/jit/valuenum.h:1324
- This change fixes a 32-bit truncation bug that can affect value numbering and assertion propagation (e.g., long constants like 0x1_0000_0000L being incorrectly treated as fitting in a 32-bit type). Since this can potentially lead to incorrect optimization/miscompilation on 32-bit targets, please add a targeted JIT regression test that fails on x86 without the fix and passes with it (for example, a nested
ifwhere the outer compare isx < 0x1_0000_0000Land the inner branch checksx >= 0, validating thatx=1takes the non-negative path).
int64_t val = CoercedConstantValue<int64_t>(vn);
if (FitsIn<T>(val))
{
*value = static_cast<T>(val);
return true;
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On 32-bit targets
ssize_tis effectivelyint32_t, soCoercedConstantValue<ssize_t>truncatesTYP_LONGvalues. InIsVNIntegralConstant, this truncation occurs before theFitsIn<T>check, causing arbitraryTYP_LONGconstants to be incorrectly reported as fitting into smaller integral types (e.g. int32).Changes
src/coreclr/jit/valuenum.h: read the constant asint64_tinstead ofssize_tinIsVNIntegralConstant, preserving the full 64-bit value before theFitsIn<T>check.TYP_INTconstants are sign-extended toint64_tandTYP_LONGconstants are preserved without truncation, soFitsIn<T>now evaluates the true value on all architectures.