[llvm] [DAGCombiner] Fix the "subtraction if above a constant threshold" miscompile (PR #140042)

[Piotr Fusik via llvm-commits]

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@@ -12140,11 +12140,16 @@ SDValue DAGCombiner::visitSELECT(SDNode *N) {
     // (select (ult x, C), x, (add x, -C)) -> (umin x, (add x, -C))
     APInt C;
     if (sd_match(Cond1, m_ConstInt(C)) && hasUMin(VT)) {
-      if ((CC == ISD::SETUGT && Cond0 == N2 &&
-           sd_match(N1, m_Add(m_Specific(N2), m_SpecificInt(~C)))) ||
-          (CC == ISD::SETULT && Cond0 == N1 &&
-           sd_match(N2, m_Add(m_Specific(N1), m_SpecificInt(-C)))))
-        return DAG.getNode(ISD::UMIN, DL, VT, N1, N2);
+      if (CC == ISD::SETUGT && Cond0 == N2 &&
+          sd_match(N1, m_Add(m_Specific(N2), m_SpecificInt(~C))))
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pfusik wrote:

Done.

https://github.com/llvm/llvm-project/pull/140042