[llvm] [InstCombine] Fold (X == 0 ? Y : 0) | X to X == 0 ? Y : X (PR #138373)

[Nikita Popov via llvm-commits]

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@@ -3658,6 +3658,15 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
       return R;
   }
 
+  // (X == 0 ? Y : 0) | X -> X == 0 ? Y : X
+  // X | (X == 0 ? Y : 0) -> X == 0 ? Y : X
+  for (Value *Op : {Op0, Op1}) {
+    if (auto *SI = dyn_cast<SelectInst>(Op)) {
+      if (auto *R = FoldOpIntoSelect(I, SI, /* FoldWithMultiUse */ false))
+        return R;
+    }
+  }
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nikic wrote:

We are already calling FoldOpIntoSelect via foldBinOpIntoSelectOrPhi. But that function currently only calls FoldOpIntoSelect if the RHS is a constant.

I think to enable this fold be basically just need to lift that restriction.

https://github.com/llvm/llvm-project/pull/138373