[InstCombine] Optimize 'xor-and-select' sequence to 'or' for bool

[Qi-Hu]

Summary

xor-and-select -> or : https://alive2.llvm.org/ce/z/52ZT62

[goldstein.w.n]

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

3184

1. You can also do and case: https://alive2.llvm.org/ce/z/adHMjn (if the ~ op is the trueval).
2. This probably belongs in foldSelectOfBools.

[goldstein.w.n]

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

3184

Actually should be able to handle all 4 of these cases:
https://alive2.llvm.org/ce/z/BgAFyN

[Qi-Hu]

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

3184

Thank you for the suggestions! Actually I submitted this patch as a pull request: 66394 (which was closed due to another PR implementing the same feature). I should've closed this revision.

[Qi-Hu]

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

3184

Thank you for the suggestions! Actually I submitted this patch as a pull request: 66394 (which was closed due to another PR implementing the same feature). I should've closed this revision.

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

if (match(CondVal, m_c_LogicalAnd(m_Not(m_Value(C)), m_Value(A))) &&
                            match(SelCond->getTrueValue(),
                                  m_Not(m_Specific(SelFVal->getTrueValue())));
       if (MayNeedFreeze)
         C = Builder.CreateFreeze(C);
       return SelectInst::Create(C, B, A);
     }
   }
 
+  // select (~b & a), a, b -> or a, b
+  // only for scalar types
+  if (match(CondVal, m_And(m_Not(m_Specific(FalseVal)), m_Specific(TrueVal))) &&
+      TrueVal->getType()->isIntegerTy(1) &&
+      FalseVal->getType()->isIntegerTy(1)) {
+    return BinaryOperator::CreateOr(TrueVal, FalseVal);
+  }
+
   return nullptr;
 }
 
 // Return true if we can safely remove the select instruction for std::bit_ceil
 // pattern.
 static bool isSafeToRemoveBitCeilSelect(ICmpInst::Predicate Pred, Value *Cond0,
                                         const APInt *Cond1, Value *CtlzOp,
                                         unsigned BitWidth) {

llvm/test/Transforms/InstCombine/fold-xor-and-select-i1.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -passes=instcombine -S | FileCheck %s
 
 define i1 @max_if(i1 %a, i1 %b) {
 ; CHECK-LABEL: define i1 @max_if
 ; CHECK-SAME: (i1 [[A:%.*]], i1 [[B:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = xor i1 [[B]], true
-; CHECK-NEXT:    [[CMP:%.*]] = and i1 [[TMP1]], [[A]]
-; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[CMP]], i1 [[A]], i1 [[B]]
-; CHECK-NEXT:    ret i1 [[TMP2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = or i1 [[A]], [[B]]
+; CHECK-NEXT:    ret i1 [[TMP1]]
 ;
   %1 = xor i1 %b, true
   %cmp = and i1 %1, %a
   %2 = select i1 %cmp, i1 %a, i1 %b
   ret i1 %2
 }