When combining consecutive stores allow loads in between the stores, if the loads do not alias.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168832 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -291,6 +291,10 @@ namespace {
                  unsigned SrcValueAlign2,
                  const MDNode *TBAAInfo2) const;
 
+    /// isAlias - Return true if there is any possibility that the two addresses
+    /// overlap.
+    bool isAlias(LSBaseSDNode *Op0, LSBaseSDNode *Op1);
+
     /// FindAliasInfo - Extracts the relevant alias information from the memory
     /// node.  Returns true if the operand was a load.
     bool FindAliasInfo(SDNode *N,
@@ -7552,7 +7556,14 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode* St) {
   if (BasePtr.first.getOpcode() == ISD::UNDEF)
     return false;
 
+  // Save the LoadSDNodes that we find in the chain.
+  // We need to make sure that these nodes do not interfere with
+  // any of the store nodes.
+  SmallVector<LSBaseSDNode*, 8> AliasLoadNodes;
+
+  // Save the StoreSDNodes that we find in the chain.
   SmallVector<MemOpLink, 8> StoreNodes;
+
   // Walk up the chain and look for nodes with offsets from the same
   // base pointer. Stop when reaching an instruction with a different kind
   // or instruction which has a different base pointer.
@@ -7596,8 +7607,26 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode* St) {
     // We found a potential memory operand to merge.
     StoreNodes.push_back(MemOpLink(Index, Ptr.second, Seq++));
 
-    // Move up the chain to the next memory operation.
+    // Find the next memory operand in the chain. If the next operand in the
-    Index = dyn_cast<StoreSDNode>(Index->getChain().getNode());
+    // chain is a store then move up and continue the scan with the next
+    // memory operand. If the next operand is a load save it and use alias
+    // information to check if it interferes with anything.
+    SDNode *NextInChain = Index->getChain().getNode();
+    while (1) {
+      if (isa<StoreSDNode>(NextInChain)) {
+        // We found a store node. Use it for the next iteration.
+        Index = cast<StoreSDNode>(NextInChain);
+        break;
+      } else if (LoadSDNode *Ldn = dyn_cast<LoadSDNode>(NextInChain)) {
+        // Save the load node for later. Continue the scan.
+        AliasLoadNodes.push_back(Ldn);
+        NextInChain = Ldn->getChain().getNode();
+        continue;
+      } else {
+        Index = NULL;
+        break;
+      }
+    }
   }
 
   // Check if there is anything to merge.
@@ -7612,11 +7641,23 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode* St) {
   // store memory address.
   unsigned LastConsecutiveStore = 0;
   int64_t StartAddress = StoreNodes[0].OffsetFromBase;
-  for (unsigned i=1; i<StoreNodes.size(); ++i) {
+  for (unsigned i = 1, e = StoreNodes.size(); i < e; ++i) {
     int64_t CurrAddress = StoreNodes[i].OffsetFromBase;
     if (CurrAddress - StartAddress != (ElementSizeBytes * i))
       break;
 
+    bool Alias = false;
+    // Check if this store interferes with any of the loads that we found.
+    for (unsigned ld = 0, lde = AliasLoadNodes.size(); ld < lde; ++ld)
+      if (isAlias(AliasLoadNodes[ld], StoreNodes[i].MemNode)) {
+        Alias = true;
+        break;
+      }
+
+    // We found a load that alias with this store. Stop the sequence.
+    if (Alias)
+      break;
+
     // Mark this node as useful.
     LastConsecutiveStore = i;
   }
@@ -9680,6 +9721,23 @@ bool DAGCombiner::isAlias(SDValue Ptr1, int64_t Size1,
   return true;
 }
 
+bool DAGCombiner::isAlias(LSBaseSDNode *Op0, LSBaseSDNode *Op1) {
+  SDValue Ptr0, Ptr1;
+  int64_t Size0, Size1;
+  const Value *SrcValue0, *SrcValue1;
+  int SrcValueOffset0, SrcValueOffset1;
+  unsigned SrcValueAlign0, SrcValueAlign1;
+  const MDNode *SrcTBAAInfo0, *SrcTBAAInfo1;
+  FindAliasInfo(Op0, Ptr0, Size0, SrcValue0, SrcValueOffset0,
+                SrcValueAlign0, SrcTBAAInfo0);
+  FindAliasInfo(Op1, Ptr1, Size1, SrcValue1, SrcValueOffset1,
+                SrcValueAlign1, SrcTBAAInfo1);
+  return isAlias(Ptr0, Size0, SrcValue0, SrcValueOffset0,
+               SrcValueAlign0, SrcTBAAInfo0,
+               Ptr1, Size1, SrcValue1, SrcValueOffset1,
+               SrcValueAlign1, SrcTBAAInfo1);
+}
+
 /// FindAliasInfo - Extracts the relevant alias information from the memory
 /// node.  Returns true if the operand was a load.
 bool DAGCombiner::FindAliasInfo(SDNode *N,

test/CodeGen/X86/2012-11-28-merge-store-alias.ll

@@ -0,0 +1,52 @@
+; RUN: llc < %s -march=x86-64 -mcpu=corei7 -mtriple=x86_64-pc-win64 | FileCheck %s
+
+; CHECK: merge_stores_can
+; CHECK: callq foo
+; CHECK-NEXT: xorps %xmm0, %xmm0
+; CHECK-NEXT: movups  %xmm0
+; CHECK: callq foo
+; CHECK: ret
+declare i32 @foo([10 x i32]* )
+
+define i32 @merge_stores_can() nounwind ssp {
+  %object1 = alloca [10 x i32]
+
+  %ret0 = call i32 @foo([10 x i32]* %object1) nounwind
+
+  %O1_1 = getelementptr [10 x i32]* %object1, i64 0, i32 1
+  %O1_2 = getelementptr [10 x i32]* %object1, i64 0, i32 2
+  %O1_3 = getelementptr [10 x i32]* %object1, i64 0, i32 3
+  %O1_4 = getelementptr [10 x i32]* %object1, i64 0, i32 4
+  %ld_ptr = getelementptr [10 x i32]* %object1, i64 0, i32 9
+
+  store i32 0, i32* %O1_1
+  store i32 0, i32* %O1_2
+  %ret = load  i32* %ld_ptr  ; <--- does not alias.
+  store i32 0, i32* %O1_3
+  store i32 0, i32* %O1_4
+
+  %ret1 = call i32 @foo([10 x i32]* %object1) nounwind
+
+  ret i32 %ret
+}
+
+; CHECK: merge_stores_cant
+; CHECK-NOT: xorps %xmm0, %xmm0
+; CHECK-NOT: movups  %xmm0
+; CHECK: ret
+define i32 @merge_stores_cant([10 x i32]* %in0, [10 x i32]* %in1) nounwind ssp {
+
+  %O1_1 = getelementptr [10 x i32]* %in1, i64 0, i32 1
+  %O1_2 = getelementptr [10 x i32]* %in1, i64 0, i32 2
+  %O1_3 = getelementptr [10 x i32]* %in1, i64 0, i32 3
+  %O1_4 = getelementptr [10 x i32]* %in1, i64 0, i32 4
+  %ld_ptr = getelementptr [10 x i32]* %in0, i64 0, i32 2
+
+  store i32 0, i32* %O1_1
+  store i32 0, i32* %O1_2
+  %ret = load  i32* %ld_ptr  ;  <--- may alias
+  store i32 0, i32* %O1_3
+  store i32 0, i32* %O1_4
+
+  ret i32 %ret
+}