[llvm] 1bd2cc5 - [InstCombine] Use KnownBits::udiv() helper

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2023-05-17T17:03:35+02:00
New Revision: 1bd2cc5f7b50e31746a21c678daa765c0f9b4c4d

URL: https://github.com/llvm/llvm-project/commit/1bd2cc5f7b50e31746a21c678daa765c0f9b4c4d
DIFF: https://github.com/llvm/llvm-project/commit/1bd2cc5f7b50e31746a21c678daa765c0f9b4c4d.diff

LOG: [InstCombine] Use KnownBits::udiv() helper

This produces more precise results than the ad-hoc implementation.

Noticed while trying to add a consistency assertion.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index c9c7f4a53cc8..0d0522a18349 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -808,9 +808,8 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
         return I;
       }
 
-      // Increase high zero bits from the input.
-      Known.Zero.setHighBits(
-          std::min(BitWidth, LHSKnown.Zero.countl_one() + RHSTrailingZeros));
+      Known = KnownBits::udiv(LHSKnown, KnownBits::makeConstant(*SA),
+                              cast<BinaryOperator>(I)->isExact());
     } else {
       computeKnownBits(I, Known, Depth, CxtI);
     }