Sanjay Patel 40a50f8701 [x86] avoid false dependency stall on 'sbb' with same source reg ...

This is effectively inverting the transform added with D116804
because the downside of the false dependency of something like
"sbb %eax, %eax" is much greater than the upside of eliminating
a zeroing instruction on (all?) Intel CPUs.

Differential Revision: https://reviews.llvm.org/D118843

2022-02-07 10:12:12 -05:00

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