[llvm] [IVDescriptors] Reject FindLast candidates with loop invariant conditions (PR #184340)

[Florian Hahn via llvm-commits]

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@@ -924,11 +924,15 @@ RecurrenceDescriptor::isFindPattern(Loop *TheLoop, PHINode *OrigPhi,
   //   select(cmp(), phi, value) or
   //   select(cmp(), value, phi)
   // TODO: Match selects with multi-use cmp conditions.
-  Value *NonRdxPhi = nullptr;
-  if (!match(I, m_CombineOr(m_Select(m_OneUse(m_Cmp()), m_Value(NonRdxPhi),
+  Value *Cmp = nullptr;
+  if (!match(I, m_CombineOr(m_Select(m_OneUse(m_Value(Cmp, m_Cmp())), m_Value(),
                                      m_Specific(OrigPhi)),
-                            m_Select(m_OneUse(m_Cmp()), m_Specific(OrigPhi),
-                                     m_Value(NonRdxPhi)))))
+                            m_Select(m_OneUse(m_Value(Cmp, m_Cmp())),
+                                     m_Specific(OrigPhi), m_Value()))))
+    return InstDesc(false, I);
+
+  // If the condition is loop invariant, bail out.
+  if (TheLoop->isLoopInvariant(Cmp))
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fhahn wrote:

why does it matter if the condition is loop invariant or not?

https://github.com/llvm/llvm-project/pull/184340