[JIT] ARM64 vector right-shift must dead-code eliminate if the constant is zero. #90051
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch Issue DetailsFixes #89868 The vector right-shift instructions do not allow a zero immediate value in the encoding. See the docs.
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| GetEmitter()->emitIns_R_R_I(ins, emitSize, targetReg, op2Reg, shiftAmount, opt); | ||
| if (shiftAmount == 0) | ||
| { | ||
| GetEmitter()->emitIns_R_R_R(INS_mov, emitTypeSize(node), targetReg, reg, reg); |
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We really want to use emitIns_Mov but there is an issue with the ARM64 impl that will elide the mov even if canSkip is false.
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Just checked the X64 impl and it has a similar issue.
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Why is eliding a mov an issue here?
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It breaks the jump table logic which expects a fixed number of bytes per switch case (on Arm64 that's 2 instructions per case, so 8-bytes)
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@dotnet/jit-contrib @BruceForstall this is ready. |
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Fixes #89868
The vector right-shift instructions do not allow a zero immediate value in the encoding. See the docs.