GlobalsAA: Take advantage of ArgMemOnly, InaccessibleMemOnly and InaccessibleMemOrArgMemOnly attributes

[vaivaswatha]

Summary

1. Modify AnalyzeCallGraph() to retain function info for external functions

if the function has [InaccessibleMemOr]ArgMemOnly flags.

2. When analyzing the use of a global is function parameter at a call site,

mark the callee also as modifying the global appropriately.

3. Add additional test cases.

Depends on D15499

[jmolloy]

Hi,

This looks correct to me.

Cheers,

James

[vaivaswatha]

@jmolloy Thank you for the review.

lib/Analysis/GlobalsModRef.cpp

if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
             return true;
           if (Readers)
             Readers->insert(ParentF);
           if (Writers)
             Writers->insert(ParentF);
         } else {
           return true; // Argument of an unknown call.
         }
+        // If the Callee is not ReadNone, it may read the global,
+        // and if it is not ReadOnly, it may also write to it.
+        Function *CalleeF = CS.getCalledFunction();
+        if (!CalleeF->doesNotAccessMemory()) {
+          if (Readers)
+            Readers->insert(CalleeF);
+          if (Writers && !CalleeF->onlyReadsMemory())
+            Writers->insert(CalleeF);
+        }
       }
     } else if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
       if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
         return true; // Allow comparison against null.
     } else {
       return true;
     }
   }
for (unsigned i = 0, e = SCC.size(); i != e && !KnowNothing; ++i) {
       Function *F = SCC[i]->getFunction();
       if (!F) {
         KnowNothing = true;
         break;
       }
 
       if (F->isDeclaration()) {
         // Try to get mod/ref behaviour from function attributes.
-        if (F->doesNotAccessMemory()) {
+        if (F->doesNotAccessMemory() || F->onlyAccessesInaccessibleMemory()) {
           // Can't do better than that!
         } else if (F->onlyReadsMemory()) {
           FI.addModRefInfo(MRI_Ref);
           if (!F->isIntrinsic())
             // This function might call back into the module and read a global -
             // consider every global as possibly being read by this function.
             FI.setMayReadAnyGlobal();
+        } else if (F->onlyAccessesArgMemory() || 
+                   F->onlyAccessesInaccessibleMemOrArgMem()) {
+          // This function may only access (read/write) memory pointed to by its
+          // arguments. If this pointer is to a global, this escaping use of the
+          // pointer is captured in AnalyzeUsesOfPointer().
+          FI.addModRefInfo(MRI_ModRef);
         } else {
           FI.addModRefInfo(MRI_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();
         }
         continue;
       }

test/Analysis/GlobalsModRef/argmemonly-escape.ll

+; RUN: opt < %s -O1 -S -enable-non-lto-gmr=true | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.10.0"
+
+@a = internal global [3 x i32] zeroinitializer, align 4
+
+; The important thing we're checking for here is the reload of (some element of)
+; @a after the memset.
+
+; CHECK-LABEL: @main
+; CHECK: load i32, i32* getelementptr {{.*}} @a
+; CHECK-NEXT: call void @memsetp0i8i64{{.*}} @a
+; CHECK-NEXT: load i32, i32* getelementptr {{.*}} @a
+; CHECK-NEXT: call void @memsetp0i8i64A{{.*}} @a
+; CHECK-NEXT: load i32, i32* getelementptr {{.*}} @a
+; CHECK: icmp eq
+; CHECK: br i1
+
+define i32 @main() {
+entry:
+  %0 = bitcast [3 x i32]* @a to i8*
+  %1 = load i32, i32* getelementptr inbounds ([3 x i32], [3 x i32]* @a, i64 0, i64 2), align 4
+  call void @memsetp0i8i64(i8* %0, i8 0, i64 4, i32 4, i1 false)
+  %2 = load i32, i32* getelementptr inbounds ([3 x i32], [3 x i32]* @a, i64 0, i64 2), align 4
+  call void @memsetp0i8i64A(i8* %0, i8 0, i64 4, i32 4, i1 false)
+  %3 = load i32, i32* getelementptr inbounds ([3 x i32], [3 x i32]* @a, i64 0, i64 2), align 4
+  %4 = add i32 %2, %3
+  %cmp1 = icmp eq i32 %1, %4
+  br i1 %cmp1, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entr
+  call void @abort() #3
+  unreachable
+
+if.end:                                           ; preds = %entry
+  ret i32 0
+}
+
+; Function Attrs: nounwind argmemonly
+declare void @memsetp0i8i64(i8* nocapture, i8, i64, i32, i1) nounwind argmemonly
+
+; Function Attrs: nounwind inaccessiblemem_or_argmemonly
+declare void @memsetp0i8i64A(i8* nocapture, i8, i64, i32, i1) nounwind inaccessiblemem_or_argmemonly
+
+; Function Attrs: noreturn nounwind
+declare void @abort() noreturn nounwind

test/Analysis/GlobalsModRef/modreftest.ll

; CHECK-NEXT: ret i32 12
   call void @doesnotmodX( )
   %V = load i32, i32* @X    ; <i32> [#uses=1]
   ret i32 %V
 }
 
 define void @doesnotmodX() {
   ret void
 }
+
+declare void @InaccessibleMemOnlyFunc( ) #0
+declare void @InaccessibleMemOrArgMemOnlyFunc( ) #1
+
+define i32 @test2(i32* %P) {
+; CHECK:      @test2
+; CHECK-NEXT: store i32 12, i32* @X
+; CHECK-NEXT: call void @InaccessibleMemOnlyFunc()
+; CHECK-NEXT: call void @InaccessibleMemOrArgMemOnlyFunc()
+; CHECK-NOT:  load i32
+; CHECK-NEXT: ret i32 12
+  store i32 12, i32* @X
+  call void @InaccessibleMemOnlyFunc( )
+        call void @InaccessibleMemOrArgMemOnlyFunc( )
+  %V = load i32, i32* @X    ; <i32> [#uses=1]
+  ret i32 %V
+}
+
+attributes #0 = { inaccessiblememonly }
+attributes #1 = { inaccessiblemem_or_argmemonly }