Clang emits debug info for multiple (at least D/C1 and D/C2) dtor/ctor functions

[dwblaikie]

Bugzilla Link	14610
Version	trunk
OS	Linux
Blocks	#14702 llvm/llvm-bugzilla-archive#24345
CC	@DougGregor,@echristo

Extended Description

Reduced from the GDB 7.5 test gdb.cp/mb-ctor.cc:

#include
struct Base {
~Base() {
printf("~Base\n");
}
};

struct Derived : virtual Base {
~Derived();
};

Derived::~Derived() {
printf("~Derived\n");
}

int main() {
Derived d;
}

breaking on "Derived::~Derived()" in GDB with Clang debug info causes this program to break twice. With GCC's debug info the program only breaks once.

From the DWARF dump it looks like Clang is emitting debug info (DW_TAG_subprogram and line table entries) for both the D1 and D2 version of the function, both with a DW_AT_specification of the DW_TAG_subprogram named "~Derived". I assume this is why GDB breaks twice.

I can't quite do a direct comparison to GCC & see which function it's emitted debug info for because it seems to have inlined the dtor call, even at -O0, so I can't match it to a particular exported symbol.

[dwblaikie]

Not sure what the answer will be here.

Based on some experiments Richard Smith helped me with:
Clang implements D1 by calling D2.
GCC implements D1 and D2 by duplicating the code entirely (even under -Os).

That means that breaking in the dtor with GCC debug info will only break once (in either D1 or D2). Clang will end up breaking twice.

One theory is that we could mark D1 as artificial - not sure if that would produce the desired effect, but might.

[dwblaikie]

I'll cover ctors with this bug too, rather than filing another.

Shows up in gdb.cp/expand-sals.exp while looking at the backtrace of a breakpoint in a ctor & observing an extra, unexpected, stack frame.

[llvmbot]

mentioned in issue llvm/llvm-bugzilla-archive#24345

[llvmbot]

@llvm/issue-subscribers-debuginfo

Author: David Blaikie (dwblaikie)

| | | | --- | --- | | Bugzilla Link | [14610](https://llvm.org/bz14610) | | Version | trunk | | OS | Linux | | Blocks | llvm/llvm-project#14702 llvm/llvm-bugzilla-archive#24345 | | CC | @DougGregor,@echristo |

Extended Description

Reduced from the GDB 7.5 test gdb.cp/mb-ctor.cc:

#include <cstdio>
struct Base {
~Base() {
printf("~Base\n");
}
};

struct Derived : virtual Base {
~Derived();
};

Derived::~Derived() {
printf("~Derived\n");
}

int main() {
Derived d;
}

breaking on "Derived::~Derived()" in GDB with Clang debug info causes this program to break twice. With GCC's debug info the program only breaks once.

From the DWARF dump it looks like Clang is emitting debug info (DW_TAG_subprogram and line table entries) for both the D1 and D2 version of the function, both with a DW_AT_specification of the DW_TAG_subprogram named "~Derived". I assume this is why GDB breaks twice.

I can't quite do a direct comparison to GCC & see which function it's emitted debug info for because it seems to have inlined the dtor call, even at -O0, so I can't match it to a particular exported symbol.