[GlobalOpt] Sort members of llvm.used deterministically

[JakeVanAdrighem]

Summary

Fix the way we sort the llvm.used and llvm.compiler.used members.

This bug seems to have been introduced in rL183756 through a set of improper casts to GlobalValue*. In subsequent patches this problem was missed and transformed into a getName call on a ConstantExpr.

[silvas]

How did you find this?

[JakeVanAdrighem]

When iterating with a set of passes manually, I found that GlobalOpt was not reaching a fixed point but was not reporting any changes.

[silvas]

LGTM. Any idea why this wasn't causing test failures from unstable qsort's?

[JakeVanAdrighem]

I think it was able to avoid test failure simply because there are so few elements in the existing test that compareNames in qsort just happened to produce the same results each time.

[silvas]

Makes sense. Do you need me to commit this for you?

• Sean Silva

[JakeVanAdrighem]

If you could, please.

llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp

if (EvalSuccess) {
     for (GlobalVariable *GV : Eval.getInvariants())
       GV->setConstant(true);
   }
 
   return EvalSuccess;
 }
 
 static int compareNames(Constant *const *A, Constant *const *B) {
-  return (*A)->getName().compare((*B)->getName());
+  return (*A)->stripPointerCasts()->getName().compare(
+      (*B)->stripPointerCasts()->getName());
 }
 
 static void setUsedInitializer(GlobalVariable &V,
                                const SmallPtrSet<GlobalValue *, 8> &Init) {
   if (Init.empty()) {
     V.eraseFromParent();
     return;
   }

llvm/trunk/test/Transforms/GlobalOpt/alias-used.ll

 ; RUN: opt < %s -globalopt -S | FileCheck %s
 
 @c = global i8 42
 
 @i = internal global i8 42
 ; CHECK: @ia = internal global i8 42
 @ia = internal alias i8, i8* @i
 
 @llvm.used = appending global [3 x i8*] [i8* bitcast (void ()* @fa to i8*), i8* bitcast (void ()* @f to i8*), i8* @ca], section "llvm.metadata"
-; CHECK-DAG: @llvm.used = appending global [3 x i8*] [i8* bitcast (void ()* @fa to i8*), i8* bitcast (void ()* @f to i8*), i8* @ca], section "llvm.metadata"
+; CHECK-DAG: @llvm.used = appending global [3 x i8*] [i8* @ca, i8* bitcast (void ()* @fa to i8*), i8* bitcast (void ()* @f to i8*)], section "llvm.metadata"
 
 @llvm.compiler.used = appending global [4 x i8*] [i8* bitcast (void ()* @fa3 to i8*), i8* bitcast (void ()* @fa to i8*), i8* @ia, i8* @i], section "llvm.metadata"
 ; CHECK-DAG: @llvm.compiler.used = appending global [2 x i8*] [i8* bitcast (void ()* @fa3 to i8*), i8* @ia], section "llvm.metadata"
 
 @sameAsUsed = global [3 x i8*] [i8* bitcast (void ()* @fa to i8*), i8* bitcast (void ()* @f to i8*), i8* @ca]
 ; CHECK-DAG: @sameAsUsed = global [3 x i8*] [i8* bitcast (void ()* @f to i8*), i8* bitcast (void ()* @f to i8*), i8* @c]
 
 @other = global i32* bitcast (void ()* @fa to i32*)