[GlobalsAA] Restrict ModRef result if any internal method has its address taken.

Summary:
If there are any internal methods whose address was taken, conclude there is nothing known in relation of any other internal method and a global.

Reviewers: nlopes, sanjoy.google

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69690

1 files changed, 13 insertions, 6 deletions

diff --git a/llvm/lib/Analysis/GlobalsModRef.cpp b/llvm/lib/Analysis/GlobalsModRef.cpp
index efdf9706ba3..758e8277c5d 100644
--- a/llvm/lib/Analysis/GlobalsModRef.cpp
+++ b/llvm/lib/Analysis/GlobalsModRef.cpp
@@ -286,7 +286,7 @@ GlobalsAAResult::getFunctionInfo(const Function *F) {
 void GlobalsAAResult::AnalyzeGlobals(Module &M) {
   SmallPtrSet<Function *, 32> TrackedFunctions;
   for (Function &F : M)
-    if (F.hasLocalLinkage())
+    if (F.hasLocalLinkage()) {
       if (!AnalyzeUsesOfPointer(&F)) {
         // Remember that we are tracking this global.
         NonAddressTakenGlobals.insert(&F);
@@ -294,7 +294,9 @@ void GlobalsAAResult::AnalyzeGlobals(Module &M) {
         Handles.emplace_front(*this, &F);
         Handles.front().I = Handles.begin();
         ++NumNonAddrTakenFunctions;
-      }
+      } else
+        UnknownFunctionsWithLocalLinkage = true;
+    }
 
   SmallPtrSet<Function *, 16> Readers, Writers;
   for (GlobalVariable &GV : M.globals())
@@ -526,9 +528,12 @@ void GlobalsAAResult::AnalyzeCallGraph(CallGraph &CG, Module &M) {
             FI.setMayReadAnyGlobal();
         } else {
           FI.addModRefInfo(ModRefInfo::ModRef);
-          // Can't say anything useful unless it's an intrinsic - they don't
-          // read or write global variables of the kind considered here.
-          KnowNothing = !F->isIntrinsic();
+          if (!F->onlyAccessesArgMemory())
+            FI.setMayReadAnyGlobal();
+          if (!F->isIntrinsic()) {
+            KnowNothing = true;
+            break;
+          }
         }
         continue;
       }
@@ -927,7 +932,9 @@ ModRefInfo GlobalsAAResult::getModRefInfo(const CallBase *Call,
   // global we are tracking, return information if we have it.
   if (const GlobalValue *GV =
           dyn_cast<GlobalValue>(GetUnderlyingObject(Loc.Ptr, DL)))
-    if (GV->hasLocalLinkage())
+    // If GV is internal to this IR and there is no function with local linkage
+    // that has had their address taken, keep looking for a tighter ModRefInfo.
+    if (GV->hasLocalLinkage() && !UnknownFunctionsWithLocalLinkage)
       if (const Function *F = Call->getCalledFunction())
         if (NonAddressTakenGlobals.count(GV))
           if (const FunctionInfo *FI = getFunctionInfo(F))