From ac450eb59e77deb929ea2ec9556b46fbf03a9698 Mon Sep 17 00:00:00 2001
From: Nadav Rotem <nrotem@apple.com>
Date: Thu, 6 Dec 2012 17:34:13 +0000
Subject: [PATCH] Fix a bug in the code that merges consecutive stores.
 Previously we did not check if loads that happen in between stores alias with
 the first store in the chain, only with the second store onwards.

llvm-svn: 169516
---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp      | 24 +++++++++++++---------
 .../CodeGen/X86/2012-12-06-python27-miscompile.ll  | 23 +++++++++++++++++++++
 2 files changed, 37 insertions(+), 10 deletions(-)
 create mode 100644 llvm/test/CodeGen/X86/2012-12-06-python27-miscompile.ll

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index a581fd8..6cd07c2 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7613,9 +7613,9 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode* St) {
     // information to check if it interferes with anything.
     SDNode *NextInChain = Index->getChain().getNode();
     while (1) {
-      if (isa<StoreSDNode>(NextInChain)) {
+      if (StoreSDNode *STn = dyn_cast<StoreSDNode>(NextInChain)) {
         // We found a store node. Use it for the next iteration.
-        Index = cast<StoreSDNode>(NextInChain);
+        Index = STn;
         break;
       } else if (LoadSDNode *Ldn = dyn_cast<LoadSDNode>(NextInChain)) {
         // Save the load node for later. Continue the scan.
@@ -7641,10 +7641,15 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode* St) {
   // store memory address.
   unsigned LastConsecutiveStore = 0;
   int64_t StartAddress = StoreNodes[0].OffsetFromBase;
-  for (unsigned i = 1, e = StoreNodes.size(); i < e; ++i) {
-    int64_t CurrAddress = StoreNodes[i].OffsetFromBase;
-    if (CurrAddress - StartAddress != (ElementSizeBytes * i))
-      break;
+  for (unsigned i = 0, e = StoreNodes.size(); i < e; ++i) {
+
+    // Check that the addresses are consecutive starting from the second
+    // element in the list of stores.
+    if (i > 0) {
+      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.
@@ -7653,7 +7658,6 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode* St) {
         Alias = true;
         break;
       }
-
     // We found a load that alias with this store. Stop the sequence.
     if (Alias)
       break;
@@ -9746,9 +9750,9 @@ bool DAGCombiner::isAlias(LSBaseSDNode *Op0, LSBaseSDNode *Op1) {
   FindAliasInfo(Op1, Ptr1, Size1, SrcValue1, SrcValueOffset1,
                 SrcValueAlign1, SrcTBAAInfo1);
   return isAlias(Ptr0, Size0, SrcValue0, SrcValueOffset0,
-               SrcValueAlign0, SrcTBAAInfo0,
-               Ptr1, Size1, SrcValue1, SrcValueOffset1,
-               SrcValueAlign1, SrcTBAAInfo1);
+                 SrcValueAlign0, SrcTBAAInfo0,
+                 Ptr1, Size1, SrcValue1, SrcValueOffset1,
+                 SrcValueAlign1, SrcTBAAInfo1);
 }
 
 /// FindAliasInfo - Extracts the relevant alias information from the memory
diff --git a/llvm/test/CodeGen/X86/2012-12-06-python27-miscompile.ll b/llvm/test/CodeGen/X86/2012-12-06-python27-miscompile.ll
new file mode 100644
index 0000000..d9effc9
--- /dev/null
+++ b/llvm/test/CodeGen/X86/2012-12-06-python27-miscompile.ll
@@ -0,0 +1,23 @@
+; RUN: llc < %s -march=x86 -mcpu=corei7 -mtriple=i686-pc-win32 | FileCheck %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"
+
+; Make sure that we are zeroing one memory location at a time using xorl and
+; not both using XMM registers.
+
+;CHECK: @foo
+;CHECK: xorl
+;CHECK-NOT: xmm
+;CHECK: ret
+define i32 @foo (i64* %so) nounwind uwtable ssp {
+entry:
+  %used = getelementptr inbounds i64* %so, i32 3
+  store i64 0, i64* %used, align 8
+  %fill = getelementptr inbounds i64* %so, i32 2
+  %L = load i64* %fill, align 8
+  store i64 0, i64* %fill, align 8
+  %cmp28 = icmp sgt i64 %L, 0
+  %R = sext i1 %cmp28 to i32
+  ret i32 %R
+}
-- 
2.7.4