JitArm64: Fix special cases of cmp #11564
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This fixes a regression from 592ba31. When `a` was a constant 0 and `b` was a non-constant 0x80000000, the 32-bit negation operation would overflow, causing an incorrect result. The sign extension needs to happen before the negation to avoid overflow. Note that I can't merge the SXTW and NEG into one instruction. NEG is an alias for SUB with the first operand being set to ZR, but "SUB (extended register)" treats register 31 as SP instead of ZR. I've also changed the order for the case where `a` is a constant 0xFFFFFFFF. I don't think the order actually affects correctness here, but let's use the same order for all the cases since it makes the code easier to reason about.
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This fixes Mario & Sonic at the Olympic Winter Games. |
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Oops, nice catch! 👌 |
Sintendo
approved these changes
Feb 14, 2023
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This fixes a regression from 592ba31. When
awas a constant 0 andbwas a non-constant 0x80000000, the 32-bit negation operation would overflow, causing an incorrect result. The sign extension needs to happen before the negation to avoid overflow.Note that I can't merge the SXTW and NEG into one instruction. NEG is an alias for SUB with the first operand being set to ZR, but "SUB (extended register)" treats register 31 as SP instead of ZR.
I've also changed the order for the case where
ais a constant 0xFFFFFFFF. I don't think the order actually affects correctness here, but let's use the same order for all the cases since it makes the code easier to reason about.