[llvm] c2428a4 - [InstCombine] Remove SPF min/max check from select demanded bits (NFCI)

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2022-03-01T14:50:37+01:00
New Revision: c2428a4fad3470261128fe92d79f7df8dbe6d415

URL: https://github.com/llvm/llvm-project/commit/c2428a4fad3470261128fe92d79f7df8dbe6d415
DIFF: https://github.com/llvm/llvm-project/commit/c2428a4fad3470261128fe92d79f7df8dbe6d415.diff

LOG: [InstCombine] Remove SPF min/max check from select demanded bits (NFCI)

This should no longer be necessary now that we canonicalize to
intrinsics. This may not be entirely NFC in practice if worklist
order gets inverted and we perform demanded bits simplification
of a select user before the select is canonicalized.

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 208fe68f7896c..d0a3767ae0fda 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -334,33 +334,6 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
     break;
   }
   case Instruction::Select: {
-    Value *LHS, *RHS;
-    SelectPatternFlavor SPF = matchSelectPattern(I, LHS, RHS).Flavor;
-    if (SPF == SPF_UMAX) {
-      // UMax(A, C) == A if ...
-      // The lowest non-zero bit of DemandMask is higher than the highest
-      // non-zero bit of C.
-      const APInt *C;
-      unsigned CTZ = DemandedMask.countTrailingZeros();
-      if (match(RHS, m_APInt(C)) && CTZ >= C->getActiveBits())
-        return LHS;
-    } else if (SPF == SPF_UMIN) {
-      // UMin(A, C) == A if ...
-      // The lowest non-zero bit of DemandMask is higher than the highest
-      // non-one bit of C.
-      // This comes from using DeMorgans on the above umax example.
-      const APInt *C;
-      unsigned CTZ = DemandedMask.countTrailingZeros();
-      if (match(RHS, m_APInt(C)) &&
-          CTZ >= C->getBitWidth() - C->countLeadingOnes())
-        return LHS;
-    }
-
-    // If this is a select as part of any other min/max pattern, don't simplify
-    // any further in case we break the structure.
-    if (SPF != SPF_UNKNOWN)
-      return nullptr;
-
     if (SimplifyDemandedBits(I, 2, DemandedMask, RHSKnown, Depth + 1) ||
         SimplifyDemandedBits(I, 1, DemandedMask, LHSKnown, Depth + 1))
       return I;