Path-aware TBAA produces the same mangled name for internal names


Bugzilla Link	PR17997
Status	NEW
Importance	P normal
Reported by	Reid Kleckner (rnk@google.com)
Reported on	2013-11-19 16:48:34 -0800
Last modified on	2017-08-28 00:28:48 -0700
Version	unspecified
Hardware	PC Windows NT
CC	karnajitw@gmail.com, llvm-bugs@lists.llvm.org, llvm@sunfishcode.online, mren@apple.com, rafael@espindo.la
Fixed by commit(s)
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The non-path-aware TBAA code has this fragment of code:
  if (const EnumType *ETy = dyn_cast<EnumType>(Ty)) {
    // In C++ mode, types have linkage, so we can rely on the ODR and
    // on their mangled names, if they're external.
    // TODO: Is there a way to get a program-wide unique name for a
    // decl with local linkage or no linkage?
    if (!Features.CPlusPlus || !ETy->getDecl()->isExternallyVisible())
      return MetadataCache[Ty] = getChar();

    SmallString<256> OutName;
    llvm::raw_svector_ostream Out(OutName);
    MContext.mangleTypeName(QualType(ETy, 0), Out);
    Out.flush();
    return MetadataCache[Ty] = createTBAAScalarType(OutName, getChar());
  }

Path-aware TBAA doesn't have any such condition.  Is this a problem?  Do the
names matter?  I don't see any code that combines them in lib/Linker or
lib/LTO.  You can see the issue for this program:

$ cat t.cpp
namespace {
struct Foo {
#ifdef CONFIG_1
  int a;
#endif
  int b;
};
}
int *store1();
#ifdef CONFIG_1
static Foo c;
int *store1() {
  c.b = 42;
  return &c.b;
}
#else
static Foo c;
int *store2() {
  c.b = 43;
  return &c.b;
}
int main() {
  return *store1() + *store2();
}
#endif

$ clang++ -c t.cpp -O1 -emit-llvm -S -o - -DCONFIG_1 | grep ZTS && clang++
t.cpp -c -o t2.bc -O1 -emit-llvm -o - -S | grep _ZTS
!2 = metadata !{metadata !"_ZTSN12_GLOBAL__N_13FooE", metadata !3, i64 0,
metadata !3, i64 4}
!2 = metadata !{metadata !"_ZTSN12_GLOBAL__N_13FooE", metadata !3, i64 0}

They use the same name, "_ZTSN12_GLOBAL__N_13FooE".

Quuxplusone / LLVMBugzillaTest

Path-aware TBAA produces the same mangled name for internal names #17996