3 files changed, 24 insertions, 6 deletions

diff --git a/llvm/lib/Analysis/AliasAnalysis.cpp b/llvm/lib/Analysis/AliasAnalysis.cpp
index dee9b535871..371dcafa9f3 100644
--- a/llvm/lib/Analysis/AliasAnalysis.cpp
+++ b/llvm/lib/Analysis/AliasAnalysis.cpp
@@ -116,13 +116,16 @@ AliasAnalysis::getModRefBehavior(Function *F,
       return DoesNotAccessMemory;
     if (F->onlyReadsMemory())
       return OnlyReadsMemory;
-    if (unsigned id = F->getIntrinsicID()) {
+    if (unsigned id = F->getIntrinsicID())
+      return getModRefBehavior(id);
+  }
+  return UnknownModRefBehavior;
+}
+
+AliasAnalysis::ModRefBehavior AliasAnalysis::getModRefBehavior(unsigned iid) {
 #define GET_INTRINSIC_MODREF_BEHAVIOR
 #include "llvm/Intrinsics.gen"
 #undef GET_INTRINSIC_MODREF_BEHAVIOR
-    }
-  }
-  return UnknownModRefBehavior;
 }
 
 AliasAnalysis::ModRefResult
diff --git a/llvm/lib/Target/README.txt b/llvm/lib/Target/README.txt
index 22dadfeb3dd..38c3daa9383 100644
--- a/llvm/lib/Target/README.txt
+++ b/llvm/lib/Target/README.txt
@@ -1678,8 +1678,8 @@ And functionattrs doesn't realize that the p.0 load points to function local
 memory.
 
 Also, functionattrs doesn't know about memcpy/memset.  This function should be
-marked readnone, since it only twiddles local memory, but functionattrs doesn't
-handle memset/memcpy/memmove aggressively:
+marked readnone rather than readonly, since it only twiddles local memory, but
+functionattrs doesn't handle memset/memcpy/memmove aggressively:
 
 struct X { int *p; int *q; };
 int foo() {
diff --git a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
index a16d335ef50..0bff2b94e9d 100644
--- a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -136,6 +136,21 @@ bool FunctionAttrs::AddReadAttrs(const std::vector<CallGraphNode *> &SCC) {
         // Ignore calls to functions in the same SCC.
         if (SCCNodes.count(CS.getCalledFunction()))
           continue;
+        // Ignore intrinsics that only access local memory.
+        if (unsigned id = CS.getCalledFunction()->getIntrinsicID())
+          if (AliasAnalysis::getModRefBehavior(id) ==
+              AliasAnalysis::AccessesArguments) {
+            // Check that all pointer arguments point to local memory.
+            for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
+                 CI != CE; ++CI) {
+              Value *Arg = *CI;
+              if (isa<PointerType>(Arg->getType()) && !PointsToLocalMemory(Arg))
+                // Writes memory.  Just give up.
+                return false;
+            }
+            // Only reads and writes local memory.
+            continue;
+          }
       } else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
         // Ignore loads from local memory.
         if (PointsToLocalMemory(LI->getPointerOperand()))