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JIT: Use smaller xarch mov encoding when long fits into int - #135182
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BoyBaykiller
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October 4, 2026 19:59
EgorBo
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🟡 Changes recommended
The new encoding path lacks regression coverage for emitted bytes, size, and boundary values.
Review effort: Balanced
Findings: 1
Open (1)
What changed in this PR
Optimizes x64 JIT code size by using the 7-byte sign-extending C7 encoding when a 64-bit immediate fits in int32_t.
Changes:
- Selects and sizes the shorter encoding.
- Emits
mov r/m64, imm32. - Uses
FitsIn<int32_t>for validation.
| File | Description |
|---|---|
src/coreclr/jit/emitxarch.cpp |
Implements the shorter immediate encoding. |
Comment on lines
+16967
to
+16968
| bool isSignExtendingMov = (size == EA_8BYTE) && FitsIn<int32_t>(val) && !id->idIsCnsReloc(); | ||
| if ((ins == INS_mov) && isSignExtendingMov) |
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Fixes #134012