[llvm] [ConstraintElim] Derive an unsigned IV bound from a signed relational latch. (PR #222762)

[Yingwei Zheng via llvm-commits]

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@@ -1159,6 +1159,18 @@ void State::addInfoForInductions(BasicBlock &BB) {
     WorkList.push_back(FactOrCheck::getConditionFact(
         DTN, ContinuePred, PN, B, ConditionTy(ContinuePred, StartValue, B)));
 
+    // For a non-negative backedge value, 0 s<= PN s< B implies B is
+    // non-negative as well, so the same bound holds in the unsigned system.
+    if (ICmpInst::isSigned(ContinuePred)) {
+      MonotonicInfo Info = getMonotonicityInfo(*PN, Backedge);
+      if ((Info.Signed && !Info.Decreasing) ||
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dtcxzyw wrote:

IIRC it should be `) &&` here. For decreasing sequences, `nneg Backage s> B` should not imply that B is also non-negative. Then you cannot convert the predicate into an unsigned one.



https://github.com/llvm/llvm-project/pull/222762