GetDemandedBits mostly just calls SimplifyMultipleUseDemandedBits now, but it does a very blunt constant simplification that SimplifyMultipleUseDemandedBits avoids.
If we need to demand bits from constants we should handle this through ShrinkDemandedConstant/targetShrinkDemandedConstant.
@arsenm confirmed that the sign extended immediates are better for code size.
Differential Revision: https://reviews.llvm.org/D74857
Summary:
At present, the code calculating known bits of AMDGPU MUL_I24 confuses the concepts of "non-negative number" and "positive number".
In some situations, it results in incorrect code. I have a case where the optimizer replaces the result of calculating MUL_I24(-5, 0) with -8.
Reviewers: foad, arsenm
Reviewed By: arsenm
Subscribers: foad, arsenm, kzhuravl, jvesely, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, hiraditya, llvm-commits
Tags: #llvm
Patch by Eugene Kuznetsov.
Differential Revision: https://reviews.llvm.org/D70367
Simon Pilgrim