[llvm] [ValueTracking] Handle recursive select/PHI in ComputeKnownBits (PR #114689)

[Nikita Popov via llvm-commits]

================
@@ -580,6 +580,43 @@ static bool cmpExcludesZero(CmpInst::Predicate Pred, const Value *RHS) {
   return true;
 }
 
+static void breakSelfRecursivePHI(const Use *U, const PHINode *PHI,
+                                  Value *&ValOut, Instruction *&CtxIOut,
+                                  unsigned *DepthInOut = nullptr) {
+  ValOut = U->get();
+  if (ValOut == PHI)
+    return;
+  CtxIOut = PHI->getIncomingBlock(*U)->getTerminator();
+  Value *V;
+  // If the Use is a select of this phi, compute analysis on other arm to be
+  // recusion.
+  // TODO: FMin/FMax
+  if (match(ValOut, m_Select(m_Value(), m_Specific(PHI), m_Value(V))) ||
+      match(ValOut, m_Select(m_Value(), m_Value(V), m_Specific(PHI))) ||
+      match(ValOut, m_c_MaxOrMin(m_Value(V), m_Specific(PHI)))) {
----------------
nikic wrote:

Can you please keep the extension to min/max for a separate PR? It seems unrelated to the core change here.

https://github.com/llvm/llvm-project/pull/114689