[llvm] [ConstraintElim] Handle (X | Y) >=s 0 as X >=s 0 && Y >=s 0. (PR #209743)

[Florian Hahn via llvm-commits]

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@@ -1980,6 +1980,30 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT, LoopInfo &LI,
                                      DFSInStack);
       }
 
+      // (X | Y) >=s 0 implies X >=s 0 and Y >=s 0, because the sign bit of an
+      // OR is the OR of the operand sign bits. Look through this
+      // canonicalization by InstCombine. disjunct so it is available to the
+      // solver.
+      if ((Pred == CmpInst::ICMP_SGE && match(B, m_Zero())) ||
+          (Pred == CmpInst::ICMP_SGT && match(B, m_AllOnes()))) {
+        SmallVector<Value *> OrWorklist = {A};
+        SmallPtrSet<Value *, 4> SeenOr;
+        Value *X, *Y;
+        while (!OrWorklist.empty()) {
+          Value *Cur = OrWorklist.pop_back_val();
+          if (!match(Cur, m_Or(m_Value(X), m_Value(Y))))
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fhahn wrote:

I am planning on adding support as follow-up

https://github.com/llvm/llvm-project/pull/209743