r205952 - Add global static variables for anonymous union fields. This makes
David Blaikie
dblaikie at gmail.com
Thu Apr 10 09:15:12 PDT 2014
On Wed, Apr 9, 2014 at 10:20 PM, Eric Christopher <echristo at gmail.com> wrote:
> Author: echristo
> Date: Thu Apr 10 00:20:00 2014
> New Revision: 205952
>
> URL: http://llvm.org/viewvc/llvm-project?rev=205952&view=rev
> Log:
> Add global static variables for anonymous union fields.
This loses source fidelity though, doesn't it? We no longer describe
which of these fields are mutually exclusive, etc.
We manage to get this correct for member variables that are anonymous
unions - why wouldn't the same behavior be correct for globals?
> This makes
> sure that a debugger can find them when stepping through code,
> for example from the included testcase:
Sounds like this is a debugger bug if it couldn't manage it with the
previous representation, no?
Well, actually - this looks like it might just be a compiler bug that
we accept this entity at all... gcc doesn't seem to accept this code.
I don't know why we would either. GCC 4.6, 4.7, 4.8.1, and ToT all
warn that the static anonymous struct "defines an unnamed struct/union
with no instances" (rather than introducing a global unnamed
struct/union).
Hmm, nope - just a piece of C++11 that GCC doesn't implement.
Though GCC and Clang do both implement anonymous unions at function
scope and both implement the debug info as this patch does for
globals. (with the same loss in source fidelity)
Wait, no, GCC does something weird - it includes variables directly in
the function's lexical block /and/ it includes the union:
void f() {
union { int x, y; };
...
}
looks like:
subprogram x
variable int x at location foo
variable int y at location foo
variable anon at location foo
union anon
member int x
member int y
So we've got some inconsistency here... :/
Sounds like GCC was working around the same debugger limitation but
with a little better source fidelity. If possible, I'd rather we just
fix the debugger and only produce the dwarf that describes the
source...
(haven't looked in detail at the code for this patch yet - just the
change in behavior)
>
> 12 int test_it() {
> 13 c = 1;
> 14 d = 2;
> -> 15 a = 4;
> 16 return (c == 1);
> 17 }
> 18
> (lldb) p a
> (int) $0 = 2
> (lldb) p c
> (int) $1 = 2
> (lldb) p d
> (int) $2 = 2
>
> and a, c, d are all part of the file static anonymous union:
>
> static union {
> int c;
> int d;
> union {
> int a;
> };
> struct {
> int b;
> };
> };
>
> Fixes PR19221.
>
> Added:
> cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp
> Modified:
> cfe/trunk/lib/CodeGen/CGDebugInfo.cpp
> cfe/trunk/lib/CodeGen/CGDebugInfo.h
>
> Modified: cfe/trunk/lib/CodeGen/CGDebugInfo.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGDebugInfo.cpp?rev=205952&r1=205951&r2=205952&view=diff
> ==============================================================================
> --- cfe/trunk/lib/CodeGen/CGDebugInfo.cpp (original)
> +++ cfe/trunk/lib/CodeGen/CGDebugInfo.cpp Thu Apr 10 00:20:00 2014
> @@ -3180,6 +3180,37 @@ CGDebugInfo::getOrCreateStaticDataMember
> return T;
> }
>
> +/// Recursively collect all of the member fields of a global anonymous decl and
> +/// create static variables for them. The first time this is called it needs
> +/// to be on a union and then from there we can have additional unnamed fields.
> +llvm::DIGlobalVariable
> +CGDebugInfo::CollectAnonRecordDecls(const RecordDecl *RD, llvm::DIFile Unit,
> + unsigned LineNo, StringRef LinkageName,
> + llvm::GlobalVariable *Var,
> + llvm::DIDescriptor DContext) {
> + llvm::DIGlobalVariable GV;
> +
> + for (const auto *Field : RD->fields()) {
> + llvm::DIType FieldTy = getOrCreateType(Field->getType(), Unit);
> + StringRef FieldName = Field->getName();
> +
> + // Ignore unnamed fields, but recurse into anonymous records.
> + if (FieldName.empty()) {
> + const RecordType *RT = dyn_cast<RecordType>(Field->getType());
> + if (RT)
> + GV = CollectAnonRecordDecls(RT->getDecl(), Unit, LineNo, LinkageName,
> + Var, DContext);
> + continue;
> + }
> + // Use VarDecl's Tag, Scope and Line number.
> + GV = DBuilder.createStaticVariable(DContext, FieldName, LinkageName, Unit,
> + LineNo, FieldTy,
> + Var->hasInternalLinkage(), Var,
> + llvm::DIDerivedType());
> + }
> + return GV;
> +}
> +
> /// EmitGlobalVariable - Emit information about a global variable.
> void CGDebugInfo::EmitGlobalVariable(llvm::GlobalVariable *Var,
> const VarDecl *D) {
> @@ -3200,19 +3231,35 @@ void CGDebugInfo::EmitGlobalVariable(llv
> T = CGM.getContext().getConstantArrayType(ET, ConstVal,
> ArrayType::Normal, 0);
> }
> +
> StringRef DeclName = D->getName();
> StringRef LinkageName;
> - if (D->getDeclContext() && !isa<FunctionDecl>(D->getDeclContext())
> - && !isa<ObjCMethodDecl>(D->getDeclContext()))
> + if (D->getDeclContext() && !isa<FunctionDecl>(D->getDeclContext()) &&
> + !isa<ObjCMethodDecl>(D->getDeclContext()))
> LinkageName = Var->getName();
> if (LinkageName == DeclName)
> LinkageName = StringRef();
> +
> llvm::DIDescriptor DContext =
> getContextDescriptor(dyn_cast<Decl>(D->getDeclContext()));
> - llvm::DIGlobalVariable GV = DBuilder.createStaticVariable(
> - DContext, DeclName, LinkageName, Unit, LineNo, getOrCreateType(T, Unit),
> - Var->hasInternalLinkage(), Var,
> - getOrCreateStaticDataMemberDeclarationOrNull(D));
> +
> + // Attempt to store one global variable for the declaration - even if we
> + // emit a lot of fields.
> + llvm::DIGlobalVariable GV;
> +
> + // If this is an anonymous union then we'll want to emit a global
> + // variable for each member of the anonymous union so that it's possible
> + // to find the name of any field in the union.
> + if (T->isUnionType() && DeclName.empty()) {
> + const RecordDecl *RD = cast<RecordType>(T)->getDecl();
> + assert(RD->isAnonymousStructOrUnion() && "unnamed non-anonymous struct or union?");
> + GV = CollectAnonRecordDecls(RD, Unit, LineNo, LinkageName, Var, DContext);
> + } else {
> + GV = DBuilder.createStaticVariable(
> + DContext, DeclName, LinkageName, Unit, LineNo, getOrCreateType(T, Unit),
> + Var->hasInternalLinkage(), Var,
> + getOrCreateStaticDataMemberDeclarationOrNull(D));
> + }
> DeclCache.insert(std::make_pair(D->getCanonicalDecl(), llvm::WeakVH(GV)));
> }
>
>
> Modified: cfe/trunk/lib/CodeGen/CGDebugInfo.h
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGDebugInfo.h?rev=205952&r1=205951&r2=205952&view=diff
> ==============================================================================
> --- cfe/trunk/lib/CodeGen/CGDebugInfo.h (original)
> +++ cfe/trunk/lib/CodeGen/CGDebugInfo.h Thu Apr 10 00:20:00 2014
> @@ -358,6 +358,13 @@ private:
> llvm::DIDerivedType
> getOrCreateStaticDataMemberDeclarationOrNull(const VarDecl *D);
>
> + /// Return a global variable that represents one of the collection of
> + /// global variables created for an anonmyous union.
> + llvm::DIGlobalVariable
> + CollectAnonRecordDecls(const RecordDecl *RD, llvm::DIFile Unit, unsigned LineNo,
> + StringRef LinkageName, llvm::GlobalVariable *Var,
> + llvm::DIDescriptor DContext);
> +
> /// getFunctionName - Get function name for the given FunctionDecl. If the
> /// name is constructed on demand (e.g. C++ destructor) then the name
> /// is stored on the side.
>
> Added: cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp?rev=205952&view=auto
> ==============================================================================
> --- cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp (added)
> +++ cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp Thu Apr 10 00:20:00 2014
> @@ -0,0 +1,28 @@
> +// RUN: %clang_cc1 -emit-llvm -gdwarf-4 -triple x86_64-linux-gnu %s -o - | FileCheck %s
> +
> +// Make sure that we emit a global variable for each of the members of the
> +// anonymous union.
> +
> +static union {
> + int c;
> + int d;
> + union {
> + int a;
> + };
> + struct {
> + int b;
> + };
> +};
> +
> +int test_it() {
> + c = 1;
> + d = 2;
> + a = 4;
> + return (c == 1);
> +}
> +
> +// CHECK: [[FILE:.*]] = {{.*}}[ DW_TAG_file_type ] [{{.*}}debug-info-anon-union-vars.cpp]
> +// CHECK: [[FILE]]{{.*}}[ DW_TAG_variable ] [c] [line 6] [local] [def]
> +// CHECK: [[FILE]]{{.*}}[ DW_TAG_variable ] [d] [line 6] [local] [def]
> +// CHECK: [[FILE]]{{.*}}[ DW_TAG_variable ] [a] [line 6] [local] [def]
> +// CHECK: [[FILE]]{{.*}}[ DW_TAG_variable ] [b] [line 6] [local] [def]
>
>
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