Partially address a README by having functionattrs consider calls to

memcpy, memset and other intrinsics that only access their arguments
to be readnone if the intrinsic's arguments all point to local memory.
This improves the testcase in the README to readonly, but it could in
theory be made readnone, however this would involve more sophisticated
analysis that looks through the memcpy.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92829 91177308-0d34-0410-b5e6-96231b3b80d8

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()))