[llvm] 95e4ad3 - [InstCombine] Remove redundant add+and fold (NFCI)

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2023-10-24T17:10:27+02:00
New Revision: 95e4ad3f0f6a948176e278f8e147d1667dbf58b7

URL: https://github.com/llvm/llvm-project/commit/95e4ad3f0f6a948176e278f8e147d1667dbf58b7
DIFF: https://github.com/llvm/llvm-project/commit/95e4ad3f0f6a948176e278f8e147d1667dbf58b7.diff

LOG: [InstCombine] Remove redundant add+and fold (NFCI)

This is handling a special case of demanded bits simplification
(which has multi-use support for adds, so it's not applicable in
that case either).

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 42734c42750f30e..070d386b2f18d24 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2248,13 +2248,6 @@ Instruction *InstCombinerImpl::visitAnd(BinaryOperator &I) {
 
     const APInt *AddC;
     if (match(Op0, m_Add(m_Value(X), m_APInt(AddC)))) {
-      // If we add zeros to every bit below a mask, the add has no effect:
-      // (X + AddC) & LowMaskC --> X & LowMaskC
-      unsigned Ctlz = C->countl_zero();
-      APInt LowMask(APInt::getLowBitsSet(Width, Width - Ctlz));
-      if ((*AddC & LowMask).isZero())
-        return BinaryOperator::CreateAnd(X, Op1);
-
       // If we are masking the result of the add down to exactly one bit and
       // the constant we are adding has no bits set below that bit, then the
       // add is flipping a single bit. Example: