From 5a4e11ad9c2eb9435806f93ed371e58cdb3519ba Mon Sep 17 00:00:00 2001
From: Nirav Dave <niravd@google.com>
Date: Fri, 20 Jul 2018 15:20:50 +0000
Subject: [PATCH] [DAG] Fix Memory ordering check in ReduceLoadOpStore.

When merging through a TokenFactor we need to check that the
load may be ordered such that no other aliasing memory operations may
happen. It is not sufficient to just check that the load is a member
of the chain token factor as it there may be a indirect chain. Require
the load's chain has only one use.

This fixes PR37826.

Reviewers: spatel, davide, efriedma, craig.topper, RKSimon

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D49388

llvm-svn: 337560
---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 34 ++++++++++++++-------------
 llvm/test/CodeGen/X86/pr37826.ll              | 11 ++-------
 2 files changed, 20 insertions(+), 25 deletions(-)

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 9a43aa6..60f7bcb 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -13067,22 +13067,6 @@ CheckForMaskedLoad(SDValue V, SDValue Ptr, SDValue Chain) {
   LoadSDNode *LD = cast<LoadSDNode>(V->getOperand(0));
   if (LD->getBasePtr() != Ptr) return Result;  // Not from same pointer.
 
-  // The store should be chained directly to the load or be an operand of a
-  // tokenfactor.
-  if (LD == Chain.getNode())
-    ; // ok.
-  else if (Chain->getOpcode() != ISD::TokenFactor)
-    return Result; // Fail.
-  else {
-    bool isOk = false;
-    for (const SDValue &ChainOp : Chain->op_values())
-      if (ChainOp.getNode() == LD) {
-        isOk = true;
-        break;
-      }
-    if (!isOk) return Result;
-  }
-
   // This only handles simple types.
   if (V.getValueType() != MVT::i16 &&
       V.getValueType() != MVT::i32 &&
@@ -13119,6 +13103,24 @@ CheckForMaskedLoad(SDValue V, SDValue Ptr, SDValue Chain) {
   // is aligned the same as the access width.
   if (NotMaskTZ && NotMaskTZ/8 % MaskedBytes) return Result;
 
+  // For narrowing to be valid, it must be the case that the load the
+  // immediately preceeding memory operation before the store.
+  if (LD == Chain.getNode())
+    ; // ok.
+  else if (Chain->getOpcode() == ISD::TokenFactor &&
+           SDValue(LD, 1).hasOneUse()) {
+    // LD has only 1 chain use so they are no indirect dependencies.
+    bool isOk = false;
+    for (const SDValue &ChainOp : Chain->op_values())
+      if (ChainOp.getNode() == LD) {
+        isOk = true;
+        break;
+      }
+    if (!isOk)
+      return Result;
+  } else
+    return Result; // Fail.
+
   Result.first = MaskedBytes;
   Result.second = NotMaskTZ/8;
   return Result;
diff --git a/llvm/test/CodeGen/X86/pr37826.ll b/llvm/test/CodeGen/X86/pr37826.ll
index 5718b2d..ee93d5f 100644
--- a/llvm/test/CodeGen/X86/pr37826.ll
+++ b/llvm/test/CodeGen/X86/pr37826.ll
@@ -9,19 +9,12 @@
 @e = common local_unnamed_addr global i32 0, align 4
 @.str.1 = private unnamed_addr constant [4 x i8] c"%d\0A\00", align 1
 
-; FIXME The generated code here is incorrect. We should only see a
-; single store to f (a bytes store to f+3).
+; We should only see a single store to f (a bytes store to f+3).
 define void @k(i32 %l) {
 ; CHECK-LABEL: k:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    movl {{.*}}(%rip), %eax
-; CHECK-NEXT:    movl %eax, %ecx
-; CHECK-NEXT:    andl $2097151, %ecx # imm = 0x1FFFFF
-; CHECK-NEXT:    xorl {{.*}}(%rip), %ecx
-; CHECK-NEXT:    xorl $2097151, %ecx # imm = 0x1FFFFF
-; CHECK-NEXT:    andl $-16777216, %eax # imm = 0xFF000000
-; CHECK-NEXT:    orl %ecx, %eax
-; CHECK-NEXT:    movl %eax, {{.*}}(%rip)
+; CHECK-NEXT:    orl {{.*}}(%rip), %eax
 ; CHECK-NEXT:    shrl $24, %eax
 ; CHECK-NEXT:    movb %al, f+{{.*}}(%rip)
 ; CHECK-NEXT:    retq
-- 
2.7.4