From 00acf97feb2cba053a07505dfad9116ad09aae7a Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Mon, 28 Apr 2008 19:51:27 +0000
Subject: [PATCH] Fix DSE to not eliminate volatile loads with no uses.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50370 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/DeadStoreElimination.cpp        | 6 +++---
 test/Transforms/DeadStoreElimination/volatile-load.ll | 8 ++++++++
 2 files changed, 11 insertions(+), 3 deletions(-)
 create mode 100644 test/Transforms/DeadStoreElimination/volatile-load.ll

diff --git a/lib/Transforms/Scalar/DeadStoreElimination.cpp b/lib/Transforms/Scalar/DeadStoreElimination.cpp
index f9d1205ada5..89afa911e75 100644
--- a/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -326,9 +326,9 @@ bool DSE::handleEndBlock(BasicBlock& BB,
     
     // If we encounter a use of the pointer, it is no longer considered dead
     if (LoadInst* L = dyn_cast<LoadInst>(BBI)) {
-      // However, if this load is unused, we can go ahead and remove it, and
-      // not have to worry about it making our pointer undead!
-      if (L->use_empty()) {
+      // However, if this load is unused and not volatile, we can go ahead and remove it,
+      // and not have to worry about it making our pointer undead!
+      if (L->use_empty() && !L->isVolatile()) {
         MD.removeInstruction(L);
         
         // DCE instructions only used to calculate that load
diff --git a/test/Transforms/DeadStoreElimination/volatile-load.ll b/test/Transforms/DeadStoreElimination/volatile-load.ll
new file mode 100644
index 00000000000..c458284dca7
--- /dev/null
+++ b/test/Transforms/DeadStoreElimination/volatile-load.ll
@@ -0,0 +1,8 @@
+; RUN: llvm-as < %s | opt -dse | llvm-dis | grep {volatile load}
+
+@g_1 = global i32 0
+
+define void @foo() nounwind  {
+	%t = volatile load i32* @g_1
+	ret void
+}