[llvm] [InstCombine] Improve handling of `not` and free inversion. (PR #66787)

[via llvm-commits]

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@@ -2198,12 +2198,14 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
   // (~X) - (~Y) --> Y - X
   // This is placed after the other reassociations and explicitly excludes a
   // sub-of-sub pattern to avoid infinite looping.
-  if (isFreeToInvert(Op0, Op0->hasOneUse()) &&
-      isFreeToInvert(Op1, Op1->hasOneUse()) &&
-      !match(Op0, m_Sub(m_ImmConstant(), m_Value()))) {
-    Value *NotOp0 = Builder.CreateNot(Op0);
-    Value *NotOp1 = Builder.CreateNot(Op1);
-    return BinaryOperator::CreateSub(NotOp1, NotOp0);
+  if (!match(Op0, m_Sub(m_ImmConstant(), m_Value())) &&
+      isFreeToInvert(Op0, Op0->hasOneUse())) {
+    if (Value *NotOp1 = getFreelyInverted(Op1, Op1->hasOneUse(), &Builder)) {
+      Value *NotOp0 = getFreelyInverted(Op0, Op0->hasOneUse(), &Builder);
+      assert(NotOp0 != nullptr &&
+             "isFreeToInvert desynced with getFreelyInverted");
+      return BinaryOperator::CreateSub(NotOp1, NotOp0);
+    }
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goldsteinn wrote:

Ah, yeah thats a good point.

https://github.com/llvm/llvm-project/pull/66787