Simon Pilgrim 7b03fdbd56
[X86] Add basic computeKnownBits support for X86ISD::BSR (#102474)
Resurrect https://reviews.llvm.org/D89214 (by @topperc)

The behaviour is undefined for an input of 0, otherwise the result is the position of the most significant set bit which must be in the range [0, bitwidth-1]. So any bits above log2 of bitwidth must be 0.

Fixes #74101
2024-08-09 09:32:59 +01:00
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