[LLVM][InstCombine] not (bitcast (cmp A, B) --> bitcast (!cmp A, B)

Author: paulwalker-arm

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -5096,9 +5096,17 @@ Instruction *InstCombinerImpl::foldNot(BinaryOperator &I) {
     return &I;
   }
 
+  // not (bitcast (cmp A, B) --> bitcast (!cmp A, B)
+  if (match(NotOp, m_OneUse(m_BitCast(m_Value(X)))) &&
+      match(X, m_OneUse(m_Cmp(Pred, m_Value(), m_Value())))) {
+    cast<CmpInst>(X)->setPredicate(CmpInst::getInversePredicate(Pred));
+    return new BitCastInst(X, Ty);
+  }
+
   // Move a 'not' ahead of casts of a bool to enable logic reduction:
   // not (bitcast (sext i1 X)) --> bitcast (sext (not i1 X))
-  if (match(NotOp, m_OneUse(m_BitCast(m_OneUse(m_SExt(m_Value(X)))))) && X->getType()->isIntOrIntVectorTy(1)) {
+  if (match(NotOp, m_OneUse(m_BitCast(m_OneUse(m_SExt(m_Value(X)))))) &&
+      X->getType()->isIntOrIntVectorTy(1)) {
     Type *SextTy = cast<BitCastOperator>(NotOp)->getSrcTy();
     Value *NotX = Builder.CreateNot(X);
     Value *Sext = Builder.CreateSExt(NotX, SextTy);

llvm/test/Transforms/InstCombine/not.ll

@@ -1064,10 +1064,9 @@ if.else:
 
 define i8 @invert_bitcasted_icmp(<8 x i32> %a, <8 x i32> %b) {
 ; CHECK-LABEL: @invert_bitcasted_icmp(
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sle <8 x i32> [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <8 x i32> [[A:%.*]], [[B:%.*]]
 ; CHECK-NEXT:    [[MASK_AS_INT:%.*]] = bitcast <8 x i1> [[CMP]] to i8
-; CHECK-NEXT:    [[NOT:%.*]] = xor i8 [[MASK_AS_INT]], -1
-; CHECK-NEXT:    ret i8 [[NOT]]
+; CHECK-NEXT:    ret i8 [[MASK_AS_INT]]
 ;
   %cmp = icmp sle <8 x i32> %a, %b
   %mask.as.int = bitcast <8 x i1> %cmp to i8
@@ -1107,10 +1106,9 @@ define i8 @invert_bitcasted_icmp_multi_use_2(<8 x i32> %a, <8 x i32> %b) {
 
 define i8 @invert_bitcasted_fcmp(<8 x float> %a, <8 x float> %b) {
 ; CHECK-LABEL: @invert_bitcasted_fcmp(
-; CHECK-NEXT:    [[CMP:%.*]] = fcmp olt <8 x float> [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp uge <8 x float> [[A:%.*]], [[B:%.*]]
 ; CHECK-NEXT:    [[MASK_AS_INT:%.*]] = bitcast <8 x i1> [[CMP]] to i8
-; CHECK-NEXT:    [[NOT:%.*]] = xor i8 [[MASK_AS_INT]], -1
-; CHECK-NEXT:    ret i8 [[NOT]]
+; CHECK-NEXT:    ret i8 [[MASK_AS_INT]]
 ;
   %cmp = fcmp olt <8 x float> %a, %b
   %mask.as.int = bitcast <8 x i1> %cmp to i8