FDEs for virtual thunks

[Matthew Austern]

Is there a reason that g++ generates FDEs for virtual thunks?
It doesn't seem to generate them for non-virtual thunks.  If
those FDEs are really necessary, then that's that.  If they
aren't, however, then it would be nice to get rid of them to
save space.

			--Matt


An example of what I'm talking about:

------------------- source -------------------

int does_throw = 0;

struct VB {
   virtual ~VB();
   virtual void foo();
};

struct D : public virtual VB {
   virtual void foo();
};

VB::~VB() { }
void VB::foo() { }

void D::foo() { if (does_throw) throw 137; }

------------------- assembly -------------------
(gcc3.1 on Red Hat Linux/i386 2.4.x)

$ /usr/local/gcc-3.1/bin/c++filt < matt2.s > matt2.filt.s

...
         .section        
.gnu.linkonce.t._ZTv0_n16_N1D3fooEv,"ax",@progbits
         .align 2
         .p2align 4,,15
         .weak   virtual thunk [v:0,-16] to D::foo()
         .type   virtual thunk [v:0,-16] to D::foo(),@function
virtual thunk [v:0,-16] to D::foo():
.LFB6:
         pushl   %ebp
.LCFI14:
         movl    %esp, %ebp
.LCFI15:
         subl    $8, %esp
.LCFI16:
         movl    8(%ebp), %eax
         movl    (%eax), %edx
         movl    -16(%edx), %ecx
         addl    %ecx, %eax
         movl    %eax, 8(%ebp)
         movl    %ebp, %esp
         popl    %ebp
         jmp     D::foo()
.LFE6:
.Lfe6:
         .size   virtual thunk [v:0,-16] to D::foo(),.Lfe6-virtual thunk 
[v:0,-16] to D::foo()
         .weak   VTT for D

...

.LSFDE11:
         .long   .LEFDE11-.LASFDE11
.LASFDE11:
         .long   .LASFDE11-.Lframe1
         .long   .LFB6
         .long   .LFE6-.LFB6
         .uleb128 0x0
         .byte   0x4
         .long   .LCFI14-.LFB6
         .byte   0xe
         .uleb128 0x8
         .byte   0x85
         .uleb128 0x2
         .byte   0x4
         .long   .LCFI15-.LCFI14
         .byte   0xd
         .uleb128 0x5
         .align 4
.LEFDE11:
         .ident  "GCC: (GNU) 3.1"