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

[Nikita Popov via llvm-commits]

================
@@ -1662,6 +1662,24 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
                                     m_c_UMin(m_Deferred(A), m_Deferred(B))))))
     return BinaryOperator::CreateWithCopiedFlags(Instruction::Add, A, B, &I);
 
+  // (~X) + (~Y) --> (-2 - Y) - X
+  {
+    // To ensure we can save instructions we need to ensure that we either
+    // consume both LHS/RHS (i.e they have a `not`).
+    bool ConsumesLHS, ConsumesRHS;
+    if (isFreeToInvert(LHS, LHS->hasOneUse(), ConsumesLHS) &&
+        isFreeToInvert(RHS, RHS->hasOneUse(), ConsumesRHS) && ConsumesLHS &&
+        ConsumesRHS) {
----------------
nikic wrote:

```suggestion
    if (isFreeToInvert(LHS, LHS->hasOneUse(), ConsumesLHS) && ConsumeLHS &&
        isFreeToInvert(RHS, RHS->hasOneUse(), ConsumesRHS) && ConsumesRHS) {
```
Can short-circuit the second call.

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