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

@@ -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;

test/Analysis/GlobalsModRef/2008-09-13-VolatileRead.ll

@@ -0,0 +1,9 @@
+; RUN: llvm-as < %s | opt -globalsmodref-aa -markmodref | llvm-dis | not grep read
+; PR2792
+
+@g = global i32 0		; <i32*> [#uses=1]
+
+define i32 @f() {
+	%t = volatile load i32* @g		; <i32> [#uses=1]
+	ret i32 %t
+}