[llvm] [ConstraintElim] Optimize usub.sat intrinsic based on known constraints (PR #135744)

[Yingwei Zheng via llvm-commits]

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@@ -1137,12 +1137,15 @@ void State::addInfoFor(BasicBlock &BB) {
           FactOrCheck::getCheck(DT.getNode(&BB), cast<CallInst>(&I)));
       // TODO: Check if it is possible to instead only added the min/max facts
       // when simplifying uses of the min/max intrinsics.
-      if (!isGuaranteedNotToBePoison(&I))
-        break;
+      if (isGuaranteedNotToBePoison(&I))
+        WorkList.push_back(FactOrCheck::getInstFact(DT.getNode(&BB), &I));
+      break;
+    case Intrinsic::usub_sat:
+      WorkList.push_back(
+          FactOrCheck::getCheck(DT.getNode(&BB), cast<CallInst>(&I)));
       [[fallthrough]];
     case Intrinsic::abs:
     case Intrinsic::uadd_sat:
-    case Intrinsic::usub_sat:
       WorkList.push_back(FactOrCheck::getInstFact(DT.getNode(&BB), &I));
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dtcxzyw wrote:

You can add `noundef` to parameters to avoid test regressions.
 

https://github.com/llvm/llvm-project/pull/135744