Fix a cycle in the DAG. In this code we replace multiple loads with a single load and

multiple stores with a single load. We create the wide loads and stores (and their chains)
before we remove the scalar loads and stores and fix the DAG chain. We attempted to merge
loads with a different chain. When that happened, the assumption that it is safe to RAUW
broke and a cycle was introduced.

llvm-svn: 165148

2 files changed, 50 insertions, 7 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index f03a2a9e61f..ba14a4dbb5d 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7722,7 +7722,12 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode* St) {
   unsigned LastLegalVectorType = 0;
   unsigned LastLegalIntegerType = 0;
   StartAddress = LoadNodes[0].OffsetFromBase;
-  for (unsigned i=1; i<LoadNodes.size(); ++i) {
+  SDValue FirstChain = LoadNodes[0].MemNode->getChain();
+  for (unsigned i = 1; i < LoadNodes.size(); ++i) {
+    // All loads much share the same chain.
+    if (LoadNodes[i].MemNode->getChain() != FirstChain)
+      break;
+    
     int64_t CurrAddress = LoadNodes[i].OffsetFromBase;
     if (CurrAddress - StartAddress != (ElementSizeBytes * i))
       break;
@@ -7791,16 +7796,23 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode* St) {
                                   FirstInChain->getPointerInfo(), false, false,
                                   FirstInChain->getAlignment());
 
-  // Replace the first store with the new store
-  CombineTo(EarliestOp, NewStore);
-  // Erase all other stores.
-  for (unsigned i = 0; i < NumElem ; ++i) {
+  // Replace one of the loads with the new load.
+  LoadSDNode *Ld = cast<LoadSDNode>(LoadNodes[0].MemNode);
+  DAG.ReplaceAllUsesOfValueWith(SDValue(Ld, 1),
+                                SDValue(NewLoad.getNode(), 1));
+
+  // Remove the rest of the load chains.
+  for (unsigned i = 1; i < NumElem ; ++i) {
     // Replace all chain users of the old load nodes with the chain of the new
     // load node.
     LoadSDNode *Ld = cast<LoadSDNode>(LoadNodes[i].MemNode);
-    DAG.ReplaceAllUsesOfValueWith(SDValue(Ld, 1),
-                                  SDValue(NewLoad.getNode(), 1));
+    DAG.ReplaceAllUsesOfValueWith(SDValue(Ld, 1), Ld->getChain());
+  }
 
+  // Replace the first store with the new store.
+  CombineTo(EarliestOp, NewStore);
+  // Erase all other stores.
+  for (unsigned i = 0; i < NumElem ; ++i) {
     // Remove all Store nodes.
     if (StoreNodes[i].MemNode == EarliestOp)
       continue;
diff --git a/llvm/test/CodeGen/X86/2012-10-03-DAGCycle.ll b/llvm/test/CodeGen/X86/2012-10-03-DAGCycle.ll
new file mode 100644
index 00000000000..72083c7115e
--- /dev/null
+++ b/llvm/test/CodeGen/X86/2012-10-03-DAGCycle.ll
@@ -0,0 +1,31 @@
+; RUN: llc -mtriple=x86_64-apple-macosx -mcpu=corei7 < %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.8.0"
+
+%struct.pluto.0 = type { %struct.bar.1, %struct.hoge.368* }
+%struct.bar.1 = type { %i8* }
+%i8 = type { i8 }
+%struct.hoge.368 = type { i32, i32 }
+%struct.widget.375 = type { i32, i32, %i8*, %struct.hoge.368* }
+
+define fastcc void @bar(%struct.pluto.0* %arg) nounwind uwtable ssp align 2 {
+bb:
+  %tmp1 = alloca %struct.widget.375, align 8
+  %tmp2 = getelementptr inbounds %struct.pluto.0* %arg, i64 0, i32 1
+  %tmp3 = load %struct.hoge.368** %tmp2, align 8
+  store %struct.pluto.0* %arg, %struct.pluto.0** undef, align 8
+  %tmp = getelementptr inbounds %struct.widget.375* %tmp1, i64 0, i32 2
+  %tmp4 = getelementptr %struct.pluto.0* %arg, i64 0, i32 0, i32 0
+  %tmp5 = load %i8** %tmp4, align 8
+  store %i8* %tmp5, %i8** %tmp, align 8
+  %tmp6 = getelementptr inbounds %struct.widget.375* %tmp1, i64 0, i32 3
+  store %struct.hoge.368* %tmp3, %struct.hoge.368** %tmp6, align 8
+  br i1 undef, label %bb8, label %bb7
+
+bb7:                                              ; preds = %bb
+  unreachable
+
+bb8:                                              ; preds = %bb
+  unreachable
+}