[llvm] [ValueTracking] Infer relationship for the select with ICmp (PR #66668)

[via llvm-commits]

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@@ -8883,6 +8883,29 @@ static std::optional<bool> isImpliedCondICmps(const ICmpInst *LHS,
   if (L0 == R0 && L1 == R1)
     return isImpliedCondMatchingOperands(LPred, RPred);
 
+  // Take SGT as an example:  L0:x > L1:y and C >= 0
+  //                      ==> R0:(x -nsw y) < R1:(-C) is false
+  Value *X, *Y;
+  if (((LPred == ICmpInst::ICMP_SGT || LPred == ICmpInst::ICMP_SGE) &&
+       match(R0, m_NSWSub(m_Value(X), m_Value(Y)))) ||
+      ((LPred == ICmpInst::ICMP_UGT || LPred == ICmpInst::ICMP_UGE) &&
+       match(R0, m_NUWSub(m_Value(X), m_Value(Y))))) {
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goldsteinn wrote:

Actually I misspoke, but I don't think your proofs are correct. The `nuw` on the `sub nuw i8 0, %add` forces `%add` to be 0. Likewise the `sub nuw i8 %sub, %c` essentially forces the condition you want, not the dominating predicates.

https://github.com/llvm/llvm-project/pull/66668