[CGP] Cleanup - remove redundant code in OptimizeMemoryInst. NFC

[skatkov]

Summary

optimizeMemoryInst contains a vector AddrModeInsts.

The only use of this vector is to check that all instructions are in the same block as memory instruction.
This check is guarded by PhiSeen flag, so if we traversed through phi node then we do not need to keep information in AddrModeInsts.
AddModeInsts is set first time we found some addressing mode and updated if we found new one later.
We can find next addressing mode only if we traverse phi node so all code related to update of AddModeInsts can be safely removed.

[skatkov]

ping.

[efriedma]

LGTM.

llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp

bool CodeGenPrepare::optimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
   // unprofitable PRE transformations.
   SmallVector<Value*, 8> worklist;
   SmallPtrSet<Value*, 16> Visited;
   worklist.push_back(Addr);
 
   // Use a worklist to iteratively look through PHI nodes, and ensure that
   // the addressing mode obtained from the non-PHI roots of the graph
   // are equivalent.
-  Value *Consensus = nullptr;
-  unsigned NumUsesConsensus = 0;
-  bool IsNumUsesConsensusValid = false;
+  bool AddrModeFound = false;
   bool PhiSeen = false;
   SmallVector<Instruction*, 16> AddrModeInsts;
   ExtAddrMode AddrMode;
   TypePromotionTransaction TPT(RemovedInsts);
   TypePromotionTransaction::ConstRestorationPt LastKnownGood =
       TPT.getRestorationPoint();
   while (!worklist.empty()) {
     Value *V = worklist.back();
     worklist.pop_back();
 
     // Break use-def graph loops.
     if (!Visited.insert(V).second) {
-      Consensus = nullptr;
+      AddrModeFound = false;
       break;
     }
 
     // For a PHI node, push all of its incoming values.
     if (PHINode *P = dyn_cast<PHINode>(V)) {
       for (Value *IncValue : P->incoming_values())
         worklist.push_back(IncValue);
       PhiSeen = true;
       continue;
     }
 
     // For non-PHIs, determine the addressing mode being computed.  Note that
     // the result may differ depending on what other uses our candidate
     // addressing instructions might have.
-    SmallVector<Instruction*, 16> NewAddrModeInsts;
+    AddrModeInsts.clear();
     ExtAddrMode NewAddrMode = AddressingModeMatcher::Match(
-      V, AccessTy, AddrSpace, MemoryInst, NewAddrModeInsts, *TLI, *TRI,
+        V, AccessTy, AddrSpace, MemoryInst, AddrModeInsts, *TLI, *TRI,
         InsertedInsts, PromotedInsts, TPT);
 
-    // This check is broken into two cases with very similar code to avoid using
-    // getNumUses() as much as possible. Some values have a lot of uses, so
-    // calling getNumUses() unconditionally caused a significant compile-time
-    // regression.
-    if (!Consensus) {
-      Consensus = V;
+    if (!AddrModeFound) {
+      AddrModeFound = true;
       AddrMode = NewAddrMode;
-      AddrModeInsts = NewAddrModeInsts;
       continue;
-    } else if (NewAddrMode == AddrMode) {
-      if (!IsNumUsesConsensusValid) {
-        NumUsesConsensus = Consensus->getNumUses();
-        IsNumUsesConsensusValid = true;
-      }
-
-      // Ensure that the obtained addressing mode is equivalent to that obtained
-      // for all other roots of the PHI traversal.  Also, when choosing one
-      // such root as representative, select the one with the most uses in order
-      // to keep the cost modeling heuristics in AddressingModeMatcher
-      // applicable.
-      unsigned NumUses = V->getNumUses();
-      if (NumUses > NumUsesConsensus) {
-        Consensus = V;
-        NumUsesConsensus = NumUses;
-        AddrModeInsts = NewAddrModeInsts;
-      }
+    if (NewAddrMode == AddrMode)
       continue;
-    }
 
-    Consensus = nullptr;
+    AddrModeFound = false;
     break;
   }
 
   // If the addressing mode couldn't be determined, or if multiple different
   // ones were determined, bail out now.
-  if (!Consensus) {
+  if (!AddrModeFound) {
     TPT.rollback(LastKnownGood);
     return false;
   }
   TPT.commit();
 
   // If all the instructions matched are already in this BB, don't do anything.
   // If we saw Phi node then it is not local definitely.
   if (!PhiSeen && none_of(AddrModeInsts, [&](Value *V) {