[InstCombine] Fold X!=Y ? ctz(X^Y,true) : BW -> ctz(X^Y,false)

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -1227,8 +1227,10 @@ static Value *foldSelectCttzCtlz(ICmpInst *ICI, Value *TrueVal, Value *FalseVal,
 
   // (X == 0) ? BitWidth : ctz(X)
   // (X == -1) ? BitWidth : ctz(~X)
-  if ((X != CmpLHS || !match(CmpRHS, m_Zero())) &&
-      (!match(X, m_Not(m_Specific(CmpLHS))) || !match(CmpRHS, m_AllOnes())))
+  // (X == Y) ? BitWidth : ctz(X ^ Y)
+  if (!(X == CmpLHS && match(CmpRHS, m_Zero())) &&
+      !(match(X, m_Not(m_Specific(CmpLHS))) && match(CmpRHS, m_AllOnes())) &&
+      !match(X, m_c_Xor(m_Specific(CmpLHS), m_Specific(CmpRHS))))
     return nullptr;
 
   IntrinsicInst *II = cast<IntrinsicInst>(Count);

llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll

@@ -659,10 +659,8 @@ define i16 @test_multiuse_trunc_undef(i64 %x, ptr %p) {
 
 define i64 @test_pr128441(i64 %x, i64 %y) {
 ; CHECK-LABEL: @test_pr128441(
-; CHECK-NEXT:    [[ISZERO_NOT:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[XOR:%.*]] = xor i64 [[X]], [[Y]]
-; CHECK-NEXT:    [[CTTZ:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 true)
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[ISZERO_NOT]], i64 64, i64 [[CTTZ]]
+; CHECK-NEXT:    [[XOR:%.*]] = xor i64 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[SEL:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 false)
 ; CHECK-NEXT:    ret i64 [[SEL]]
 ;
   %iszero = icmp ne i64 %x, %y
@@ -674,10 +672,8 @@ define i64 @test_pr128441(i64 %x, i64 %y) {
 
 define i64 @test_pr128441_commuted1(i64 %x, i64 %y) {
 ; CHECK-LABEL: @test_pr128441_commuted1(
-; CHECK-NEXT:    [[ISZERO_NOT:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[XOR:%.*]] = xor i64 [[Y]], [[X]]
-; CHECK-NEXT:    [[CTTZ:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 true)
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[ISZERO_NOT]], i64 64, i64 [[CTTZ]]
+; CHECK-NEXT:    [[XOR:%.*]] = xor i64 [[Y:%.*]], [[X:%.*]]
+; CHECK-NEXT:    [[SEL:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 false)
 ; CHECK-NEXT:    ret i64 [[SEL]]
 ;
   %iszero = icmp ne i64 %x, %y
@@ -689,10 +685,8 @@ define i64 @test_pr128441_commuted1(i64 %x, i64 %y) {
 
 define i64 @test_pr128441_commuted2(i64 %x, i64 %y) {
 ; CHECK-LABEL: @test_pr128441_commuted2(
-; CHECK-NEXT:    [[ISZERO:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[XOR:%.*]] = xor i64 [[X]], [[Y]]
-; CHECK-NEXT:    [[CTTZ:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 true)
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[ISZERO]], i64 64, i64 [[CTTZ]]
+; CHECK-NEXT:    [[XOR:%.*]] = xor i64 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[SEL:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 false)
 ; CHECK-NEXT:    ret i64 [[SEL]]
 ;
   %iszero = icmp eq i64 %x, %y