If a function does a volatile load from a global constant, do not

consider it to be readonly.  In fact, don't even consider it to be
readonly if it does a volatile load from an AllocaInst either (it
is debatable as to whether readonly would be correct or not in this
case; play safe for the moment).  This fixes PR8279.

llvm-svn: 117783

2 files changed, 14 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
index d4bce9e48db..39f48145af1 100644
--- a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -188,12 +188,12 @@ bool FunctionAttrs::AddReadAttrs(const CallGraphSCC &SCC) {
             continue;
           }
       } else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
-        // Ignore loads from local memory.
-        if (PointsToLocalMemory(LI->getPointerOperand()))
+        // Ignore non-volatile loads from local memory.
+        if (!LI->isVolatile() && PointsToLocalMemory(LI->getPointerOperand()))
           continue;
       } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
-        // Ignore stores to local memory.
-        if (PointsToLocalMemory(SI->getPointerOperand()))
+        // Ignore non-volatile stores to local memory.
+        if (!SI->isVolatile() && PointsToLocalMemory(SI->getPointerOperand()))
           continue;
       }
 
diff --git a/llvm/test/Transforms/FunctionAttrs/2010-10-30-volatile.ll b/llvm/test/Transforms/FunctionAttrs/2010-10-30-volatile.ll
new file mode 100644
index 00000000000..f21fabc493c
--- /dev/null
+++ b/llvm/test/Transforms/FunctionAttrs/2010-10-30-volatile.ll
@@ -0,0 +1,10 @@
+; RUN: opt < %s -functionattrs -S | FileCheck %s
+; PR8279
+
+@g = constant i32 1
+
+define void @foo() {
+; CHECK: void @foo() {
+  %tmp = volatile load i32* @g
+  ret void
+}