From e9e973018aaf93dbd21b894b404e4b3a50805479 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Mon, 29 Nov 2010 21:59:31 +0000
Subject: [PATCH] fix PR8677, patch by Jakub Staszak!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120325 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/DeadStoreElimination.cpp |  6 ++++--
 test/Transforms/DeadStoreElimination/simple.ll | 14 ++++++++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/lib/Transforms/Scalar/DeadStoreElimination.cpp b/lib/Transforms/Scalar/DeadStoreElimination.cpp
index 02df1031e60..4540ccce8c6 100644
--- a/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -235,8 +235,10 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
                                                 &BB);
       }
         
-      // If not a definite must-alias dependency, ignore it.
-      if (!InstDep.isDef())
+      // If not a definite must-alias store dependency, ignore it.  If this is a
+      // load from the same pointer, we don't want to transform load+store into
+      // a noop.
+      if (!InstDep.isDef() || !isa<StoreInst>(InstDep.getInst()))
         continue;
     }
     
diff --git a/test/Transforms/DeadStoreElimination/simple.ll b/test/Transforms/DeadStoreElimination/simple.ll
index 0a16603f55d..ab0ef7b7eb2 100644
--- a/test/Transforms/DeadStoreElimination/simple.ll
+++ b/test/Transforms/DeadStoreElimination/simple.ll
@@ -20,3 +20,17 @@ define void @test2(i32 *%p, i32 *%q) {
 ; CHECK: @test2
 ; CHECK-NEXT: store i32 20
 }
+
+
+; PR8677
+@g = global i32 1
+
+define i32 @test3(i32* %g_addr) nounwind {
+; CHECK: @test3
+; CHEcK: load i32* %g_addr
+  %g_value = load i32* %g_addr, align 4
+  store i32 -1, i32* @g, align 4
+  store i32 %g_value, i32* %g_addr, align 4
+  %tmp3 = load i32* @g, align 4
+  ret i32 %tmp3
+}