[GlobalsAA] Relax condition in checking globals as args to functions

[vaivaswatha]

Summary

Since globals may escape as function arguments (even when they have been
found to be non-escaping, because of optimizations such as memcpyoptimizer
that replaces stores with memcpy), all arguments to a function are checked
during query to make sure they are identifiable. At that time, also ensure
we return a conservative result only if the arguments don't alias to our global.

[jmolloy]

LGTM.

[vaivaswatha]

Thanks James for the review. Also you thank you for suggesting the original patch.

lib/Analysis/GlobalsModRef.cpp

ModRefInfo GlobalsAAResult::getModRefInfoForArgument(ImmutableCallSite CS,
   
   // Iterate through all the arguments to the called function. If any argument
   // is based on GV, return the conservative result.
   for (auto &A : CS.args()) {
     SmallVector<Value*, 4> Objects;
     GetUnderlyingObjects(A, Objects, DL);
     
     // All objects must be identified.
-    if (!std::all_of(Objects.begin(), Objects.end(), isIdentifiedObject))
+    if (!std::all_of(Objects.begin(), Objects.end(), isIdentifiedObject) &&
+        // Try ::alias to see if all objects are known not to alias GV.
+        !std::all_of(Objects.begin(), Objects.end(), [&](Value *V) {
+          return this->alias(MemoryLocation(V), MemoryLocation(GV)) == NoAlias;
+          }))
       return ConservativeResult;
 
     if (std::find(Objects.begin(), Objects.end(), GV) != Objects.end())
       return ConservativeResult;
   }
 
   // We identified all objects in the argument list, and none of them were GV.
   return MRI_NoModRef;

test/Analysis/GlobalsModRef/no-escape.ll

+; RUN: opt < %s -basicaa -globals-aa -S -enable-non-lto-gmr=true -licm | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.10.0"
+
+@b = common global i32 0, align 4
+@c = internal global i32 0, align 4
+@d = common global i32 0, align 4
+@e = common global i32* null, align 4
+
+define void @foo(i32* %P) noinline {
+; CHECK: define void @foo
+  %loadp = load i32, i32* %P, align 4
+  store i32 %loadp, i32* @d, align 4
+  ret void
+}
+
+define void @bar() noinline {
+; CHECK: define void @bar
+  %loadp = load i32, i32* @d, align 4
+  store i32 %loadp, i32* @c, align 4
+  ret void
+}
+
+define i32 @main() {
+entry:
+  %retval = alloca i32, align 4
+  %c = alloca [1 x i32], align 4
+  store i32 0, i32* %retval, align 4
+  call void @bar()
+  store i32 0, i32* @b, align 4
+  br label %for.cond
+  ;; Check that @c is LICM'ed out.
+; CHECK: load i32, i32* @c
+for.cond:                                         ; preds = %for.inc, %entry
+; CHECK-LABEL: for.cond:
+; CHECK: load i32, i32* @b
+  %a1 = load i32, i32* @b, align 4
+  %aa2 = load i32, i32* @c, align 4
+  %add = add nsw i32 %a1, %aa2
+  %p1 = load i32*, i32** @e, align 4
+  call void @foo(i32* %p1)
+  %cmp = icmp slt i32 %add, 3
+  br i1 %cmp, label %for.body, label %for.end
+
+for.body:                                         ; preds = %for.cond
+  %a2 = load i32, i32* @b, align 4
+  %idxprom = sext i32 %a2 to i64
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body
+  %a3 = load i32, i32* @b, align 4
+  %inc = add nsw i32 %a3, 1
+  store i32 %inc, i32* @b, align 4
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  ret i32 0
+}
+
+; Function Attrs: nounwind argmemonly
+declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) nounwind argmemonly
+
+; Function Attrs: noreturn nounwind
+declare void @abort() noreturn nounwind