[PATCH] D18909: Cleanup Store Merging in UseAA case

[Nirav Dave via llvm-commits]

niravd created this revision.
niravd added a reviewer: jyknight.
niravd added a subscriber: llvm-commits.

This patch introduces a simpler merging of component stores in the case
of using anti-aliasing where all stores are parallel on the chain
sub-DAG. The old code remains for chains of stores but can be removed
after we obviate the need for handling that case.

http://reviews.llvm.org/D18909

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -11226,28 +11226,36 @@
                                   false, false,
                                   FirstInChain->getAlignment());
 
-  // Replace the last store with the new store
-  CombineTo(LatestOp, NewStore);
-  // Erase all other stores.
-  for (unsigned i = 0; i < NumStores; ++i) {
-    if (StoreNodes[i].MemNode == LatestOp)
-      continue;
-    StoreSDNode *St = cast<StoreSDNode>(StoreNodes[i].MemNode);
-    // ReplaceAllUsesWith will replace all uses that existed when it was
-    // called, but graph optimizations may cause new ones to appear. For
-    // example, the case in pr14333 looks like
-    //
-    //  St's chain -> St -> another store -> X
-    //
-    // And the only difference from St to the other store is the chain.
-    // When we change it's chain to be St's chain they become identical,
-    // get CSEed and the net result is that X is now a use of St.
-    // Since we know that St is redundant, just iterate.
-    while (!St->use_empty())
-      DAG.ReplaceAllUsesWith(SDValue(St, 0), St->getChain());
-    deleteAndRecombine(St);
+  bool UseAA = CombinerAA.getNumOccurrences() > 0 ? CombinerAA
+                                                  : DAG.getSubtarget().useAA();
+  if(UseAA){
+    // Replace all merged stores with the new store
+    for (unsigned i = 0; i < NumStores; ++i)
+      CombineTo(StoreNodes[i].MemNode, NewStore);
+  }
+  else{
+    // Replace the last store with the new store
+    CombineTo(LatestOp, NewStore);
+    // Erase all other stores.
+    for (unsigned i = 0; i < NumStores; ++i) {
+      if (StoreNodes[i].MemNode == LatestOp)
+        continue;
+      StoreSDNode *St = cast<StoreSDNode>(StoreNodes[i].MemNode);
+      // ReplaceAllUsesWith will replace all uses that existed when it was
+      // called, but graph optimizations may cause new ones to appear. For
+      // example, the case in pr14333 looks like
+      //
+      //  St's chain -> St -> another store -> X
+      //
+      // And the only difference from St to the other store is the chain.
+      // When we change it's chain to be St's chain they become identical,
+      // get CSEed and the net result is that X is now a use of St.
+      // Since we know that St is redundant, just iterate.
+      while (!St->use_empty())
+        DAG.ReplaceAllUsesWith(SDValue(St, 0), St->getChain());
+      deleteAndRecombine(St);
+    }
   }
-
   return true;
 }
 
@@ -11778,16 +11786,23 @@
                                   SDValue(NewLoad.getNode(), 1));
   }
 
-  // Replace the last store with the new store.
-  CombineTo(LatestOp, NewStore);
-  // Erase all other stores.
-  for (unsigned i = 0; i < NumElem ; ++i) {
-    // Remove all Store nodes.
-    if (StoreNodes[i].MemNode == LatestOp)
-      continue;
-    StoreSDNode *St = cast<StoreSDNode>(StoreNodes[i].MemNode);
-    DAG.ReplaceAllUsesOfValueWith(SDValue(St, 0), St->getChain());
-    deleteAndRecombine(St);
+  if (UseAA){
+    // Replace the all stores with the new store.
+    for (unsigned i = 0; i < NumElem; ++i)
+      CombineTo(StoreNodes[i].MemNode, NewStore);
+  }
+  else{
+    // Replace the last store with the new store.
+    CombineTo(LatestOp, NewStore);
+    // Erase all other stores.
+    for (unsigned i = 0; i < NumElem ; ++i) {
+      // Remove all Store nodes.
+      if (StoreNodes[i].MemNode == LatestOp)
+        continue;
+      StoreSDNode *St = cast<StoreSDNode>(StoreNodes[i].MemNode);
+      DAG.ReplaceAllUsesOfValueWith(SDValue(St, 0), St->getChain());
+      deleteAndRecombine(St);
+    }
   }
 
   return true;


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