[FPBuiltinFnSelection] Fold fdiv-by-exact-reciprocal-constant to fmul - #22948
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llvm.fpbuiltin.fdiv hides the division from InstCombine's foldFDivConstantDivisor until this pass lowers it to a real fdiv late in the pipeline, so InstCombine never gets a second look. Replicate the exact-reciprocal case of that fold here so X / C becomes X * (1/C) whenever C has an exact FP inverse.
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@jcranmer-intel, friendly reminder - I'm waiting your feedback on this PR. |
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In theory, with the max-error information, we could be more aggressive about the actual error in the transformation and whether or not it would be acceptable. But that can be left for a follow-up.
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llvm.fpbuiltin.fdiv hides the division from InstCombine's
foldFDivConstantDivisor until this pass lowers it to a real fdiv late
in the pipeline, so InstCombine never gets a second look. Replicate
the exact-reciprocal case of that fold here so X / C becomes X * (1/C)
whenever C has an exact FP inverse.
JIRA: CMPLRLLVM-77622