Re: increase in object code size

[John Carr <jfc@mit.edu>]

> > On 80386, -fno-exceptions reduces size by about 25%.
> 
> That much?  On sparc-sun-solaris2.5.1, size -A on a stripped cc1 from the
> latest snapshot gives
> 
> section         size         addr
> .text        1537124       166460
> .eh_frame      72120      1980396
> 
> .eh_frame is only 4.7% of .text here.  Is the bloat that much larger
> for x86?  Why?

On x86 every stack push requires a 7 byte entry in the traceback table
so the unwinder knows how to adjust the stack pointer to find the
return address.

The first optimization which comes to mind: an exception table entry
which does not apply to an instruction which can throw an exception
should be eliminated.  In GNU C and C++ (and, I think, GNU Ada) only
function calls throw exceptions.  That means there needs to be at most
one table entry per function call.

The second (x86 only): if a function does not have any exception
handlers and it has a frame pointer the unwinder does not need an
exception table.  The return PC is at a known offset from the frame
pointer.

("exception handler" here includes implicitly defined handlers in C++
to call destructors for local variables.)