From 14a498a48677eb1eaddd8329330df073224f9575 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Tue, 3 Aug 2010 17:27:43 +0000
Subject: [PATCH] Make AliasAnalysis::getModRefInfo conservative in the face of
 volatility.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110120 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/AliasAnalysis.cpp | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/lib/Analysis/AliasAnalysis.cpp b/lib/Analysis/AliasAnalysis.cpp
index 503fbbdab8d..60ea2b4ba90 100644
--- a/lib/Analysis/AliasAnalysis.cpp
+++ b/lib/Analysis/AliasAnalysis.cpp
@@ -78,8 +78,17 @@ AliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
 
 AliasAnalysis::ModRefResult
 AliasAnalysis::getModRefInfo(LoadInst *L, Value *P, unsigned Size) {
-  return alias(L->getOperand(0), getTypeStoreSize(L->getType()),
-               P, Size) ? Ref : NoModRef;
+  // If the load address doesn't alias the given address, it doesn't read
+  // or write the specified memory.
+  if (!alias(L->getOperand(0), getTypeStoreSize(L->getType()), P, Size))
+    return NoModRef;
+
+  // Be conservative in the face of volatile.
+  if (L->isVolatile())
+    return ModRef;
+
+  // Otherwise, a load just reads.
+  return Ref;
 }
 
 AliasAnalysis::ModRefResult
@@ -90,9 +99,17 @@ AliasAnalysis::getModRefInfo(StoreInst *S, Value *P, unsigned Size) {
              getTypeStoreSize(S->getOperand(0)->getType()), P, Size))
     return NoModRef;
 
+  // Be conservative in the face of volatile.
+  if (S->isVolatile())
+    return ModRef;
+
   // If the pointer is a pointer to constant memory, then it could not have been
   // modified by this store.
-  return pointsToConstantMemory(P) ? NoModRef : Mod;
+  if (pointsToConstantMemory(P))
+    return NoModRef;
+
+  // Otherwise, a store just writes.
+  return Mod;
 }
 
 AliasAnalysis::ModRefBehavior
-- 
2.34.1