From 2e7d38192de6ccdc54cf138fabdf00b81a6cd11d Mon Sep 17 00:00:00 2001
From: Nadav Rotem <nrotem@apple.com>
Date: Wed, 3 Oct 2012 19:30:31 +0000
Subject: 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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165148 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

(limited to 'lib/CodeGen/SelectionDAG/DAGCombiner.cpp')

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index f03a2a9e61..ba14a4dbb5 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/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;
-- 
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