From b8ca4ff6439c1543a0c6729cbcd6c70c3be7dc3c Mon Sep 17 00:00:00 2001
From: Duncan Sands <baldrick@free.fr>
Date: Sat, 13 Sep 2008 12:45:50 +0000
Subject: Fix PR2792: treat volatile loads as writing memory somewhere. Treat
 stores as reading memory, just to play safe.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56188 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/IPA/GlobalsModRef.cpp | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

(limited to 'lib/Analysis/IPA/GlobalsModRef.cpp')

diff --git a/lib/Analysis/IPA/GlobalsModRef.cpp b/lib/Analysis/IPA/GlobalsModRef.cpp
index 390a602..74327d5 100644
--- a/lib/Analysis/IPA/GlobalsModRef.cpp
+++ b/lib/Analysis/IPA/GlobalsModRef.cpp
@@ -431,12 +431,20 @@ void GlobalsModRef::AnalyzeCallGraph(CallGraph &CG, Module &M) {
       for (inst_iterator II = inst_begin(SCC[i]->getFunction()),
              E = inst_end(SCC[i]->getFunction());
            II != E && FunctionEffect != ModRef; ++II)
-        if (isa<LoadInst>(*II))
+        if (isa<LoadInst>(*II)) {
           FunctionEffect |= Ref;
-        else if (isa<StoreInst>(*II))
+          if (cast<LoadInst>(*II).isVolatile())
+            // Volatile loads may have side-effects, so mark them as writing
+            // memory (for example, a flag inside the processor).
+            FunctionEffect |= Mod;
+        } else if (isa<StoreInst>(*II)) {
           FunctionEffect |= Mod;
-        else if (isa<MallocInst>(*II) || isa<FreeInst>(*II))
+          if (cast<StoreInst>(*II).isVolatile())
+            // Treat volatile stores as reading memory somewhere.
+            FunctionEffect |= Ref;
+        } else if (isa<MallocInst>(*II) || isa<FreeInst>(*II)) {
           FunctionEffect |= ModRef;
+        }
 
     if ((FunctionEffect & Mod) == 0)
       ++NumReadMemFunctions;
-- 
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