r205651 - DebugInfo: PR19298: function local const variables duplicated in the root scope

[David Blaikie]

Hmm - this might not be the right long-term fix.

We still have basically the same bug for a global const int:

const int i = 3;
void func(int*);
int main() {
  func(&i); // references the global variable
  return i; // references the Constant
}

from this Clang describes two global variables and LLVM produces debug
info describing both...

I suppose what we want is to emit the constant location description
when the variable itself is not emitted (such as when the address
doesn't escape) and otherwise emit the global memory location....
perhaps a simple frontend lookup-and-replacement would suffice. Except
in cases where the global variable is emitted initially and then
optimized away by LLVM...

oh, and we don't put the constant in the right namespace - but I'll
probably just fix that immediately, even if the broader issue still
stands :/

On Fri, Apr 4, 2014 at 1:56 PM, David Blaikie <dblaikie at gmail.com> wrote:
> Author: dblaikie
> Date: Fri Apr  4 15:56:17 2014
> New Revision: 205651
>
> URL: http://llvm.org/viewvc/llvm-project?rev=205651&view=rev
> Log:
> DebugInfo: PR19298: function local const variables duplicated in the root scope
>
> See the comment for CodeGenFunction::tryEmitAsConstant that describes
> how in some contexts (lambdas) we must not emit references to the
> variable, but instead use the constant directly - because of this we end
> up emitting a constant for the variable, as well as emitting the
> variable itself.
>
> Should we just skip putting the variable on the stack at all and omit
> the debug info for the constant? It's not clear to me - what if the
> address of the local is taken?
>
> Modified:
>     cfe/trunk/lib/CodeGen/CGDebugInfo.cpp
>     cfe/trunk/test/CodeGenCXX/debug-info.cpp
>
> Modified: cfe/trunk/lib/CodeGen/CGDebugInfo.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGDebugInfo.cpp?rev=205651&r1=205650&r2=205651&view=diff
> ==============================================================================
> --- cfe/trunk/lib/CodeGen/CGDebugInfo.cpp (original)
> +++ cfe/trunk/lib/CodeGen/CGDebugInfo.cpp Fri Apr  4 15:56:17 2014
> @@ -3227,6 +3227,9 @@ void CGDebugInfo::EmitGlobalVariable(con
>    // Do not use DIGlobalVariable for enums.
>    if (Ty.getTag() == llvm::dwarf::DW_TAG_enumeration_type)
>      return;
> +  // Do not emit separate definitions for function local const/statics.
> +  if (isa<FunctionDecl>(VD->getDeclContext()))
> +    return;
>    llvm::DIGlobalVariable GV = DBuilder.createStaticVariable(
>        Unit, Name, Name, Unit, getLineNumber(VD->getLocation()), Ty, true, Init,
>        getOrCreateStaticDataMemberDeclarationOrNull(cast<VarDecl>(VD)));
>
> Modified: cfe/trunk/test/CodeGenCXX/debug-info.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/debug-info.cpp?rev=205651&r1=205650&r2=205651&view=diff
> ==============================================================================
> --- cfe/trunk/test/CodeGenCXX/debug-info.cpp (original)
> +++ cfe/trunk/test/CodeGenCXX/debug-info.cpp Fri Apr  4 15:56:17 2014
> @@ -51,11 +51,6 @@ namespace VirtualBase {
>    }
>  }
>
> -void foo() {
> -  const wchar_t c = L'x';
> -  wchar_t d = c;
> -}
> -
>  namespace b5249287 {
>  template <typename T> class A {
>    struct B;
> @@ -88,6 +83,13 @@ foo func(foo f) {
>  // CHECK: [[FUNC:![0-9]*]] = {{.*}} metadata !"_ZN7pr147634funcENS_3fooE", i32 {{[0-9]*}}, metadata [[FUNC_TYPE:![0-9]*]], {{.*}} ; [ DW_TAG_subprogram ] {{.*}} [def] [func]
>  }
>
> +void foo() {
> +  const wchar_t c = L'x';
> +  wchar_t d = c;
> +}
> +
> +// CHECK-NOT: ; [ DW_TAG_variable ] [c]
> +
>  namespace pr9608 { // also pr9600
>  struct incomplete;
>  incomplete (*x)[3];
> @@ -96,9 +98,11 @@ incomplete (*x)[3];
>  // CHECK: [[INCARRAY]] = {{.*}}metadata !"_ZTSN6pr960810incompleteE", metadata {{![0-9]*}}, i32 0, null, null, null} ; [ DW_TAG_array_type ] [line 0, size 0, align 0, offset 0] [from _ZTSN6pr960810incompleteE]
>  }
>
> -// For some reason the argument for PR14763 ended up all the way down here
> +// For some reason function arguments ended up down here
>  // CHECK: = metadata !{i32 {{[0-9]*}}, metadata [[FUNC]], {{.*}}, metadata !"[[FOO]]", i32 8192, i32 0} ; [ DW_TAG_arg_variable ] [f]
>
> +// CHECK: ; [ DW_TAG_auto_variable ] [c]
> +
>  namespace pr16214 {
>  struct a {
>    int i;
>
>
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