[InstCombine] Negator: freeze is freely negatible if it's operand is negatible

Author: LebedevRI

llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp

@@ -244,6 +244,13 @@ LLVM_NODISCARD Value *Negator::visitImpl(Value *V, unsigned Depth) {
   }
 
   switch (I->getOpcode()) {
+  case Instruction::Freeze: {
+    // `freeze` is negatible if its operand is negatible.
+    Value *NegOp = negate(I->getOperand(0), Depth + 1);
+    if (!NegOp) // Early return.
+      return nullptr;
+    return Builder.CreateFreeze(NegOp, I->getName() + ".neg");
+  }
   case Instruction::PHI: {
     // `phi` is negatible if all the incoming values are negatible.
     auto *PHI = cast<PHINode>(I);

llvm/test/Transforms/InstCombine/sub-of-negatible.ll

@@ -1214,9 +1214,9 @@ define i8 @dont_negate_ordinary_select(i8 %x, i8 %y, i8 %z, i1 %c) {
 ; Freeze is transparent as far as negation is concerned
 define i4 @negate_freeze(i4 %x, i4 %y, i4 %z) {
 ; CHECK-LABEL: @negate_freeze(
-; CHECK-NEXT:    [[T0:%.*]] = sub i4 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[T1:%.*]] = freeze i4 [[T0]]
-; CHECK-NEXT:    [[T2:%.*]] = sub i4 [[Z:%.*]], [[T1]]
+; CHECK-NEXT:    [[T0_NEG:%.*]] = sub i4 [[Y:%.*]], [[X:%.*]]
+; CHECK-NEXT:    [[T1_NEG:%.*]] = freeze i4 [[T0_NEG]]
+; CHECK-NEXT:    [[T2:%.*]] = add i4 [[T1_NEG]], [[Z:%.*]]
 ; CHECK-NEXT:    ret i4 [[T2]]
 ;
   %t0 = sub i4 %x, %y