[SCEV] Fix thinko; revert a change

Author: artagnon

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -9571,14 +9571,15 @@ getConstantEvolvingPHIOperands(Instruction *UseInst, const Loop *L,
     if (!OpInst || !canConstantEvolve(OpInst, L)) return nullptr;
 
     PHINode *P = dyn_cast<PHINode>(OpInst);
-    if (!P) {
+    if (!P)
       // If this operand is already visited, reuse the prior result.
       // We may have P != PHI if this is the deepest point at which the
       // inconsistent paths meet.
+      P = PHIMap.lookup(OpInst);
+    if (!P) {
       // Recurse and memoize the results, whether a phi is found or not.
       // This recursive call invalidates pointers into PHIMap.
-      P = PHIMap.lookup_or(
-          OpInst, getConstantEvolvingPHIOperands(OpInst, L, PHIMap, Depth + 1));
+      P = getConstantEvolvingPHIOperands(OpInst, L, PHIMap, Depth + 1);
       PHIMap[OpInst] = P;
     }
     if (!P)