On Wed, Mar 17, 2010 at 06:40:30PM +0100, Richard Guenther wrote:
> > <var_decl 0x7ffff794d140 __BLNK__
> > type <record_type 0x7ffff79493f0 SI
> > size <integer_cst 0x7ffff7854988 constant 32>
> > unit size <integer_cst 0x7ffff7854690 constant 4>
> > align 32 symtab 0 alias set -1 canonical type 0x7ffff79493f0
> > fields <field_decl 0x7ffff7946d10 i type <integer_type
> > 0x7ffff7863498 integer(kind=4)>
> > decl_2 SI file a.f90 line 4 col 0 size <integer_cst
> > 0x7ffff7854988 32> unit size <integer_cst 0x7ffff7854690 4>
> > align 32 offset_align 128
> > offset <integer_cst 0x7ffff78546b8 constant 0>
> > bit offset <integer_cst 0x7ffff7854d98 constant 0> context
> > <record_type 0x7ffff79493f0>>>
> > public static ignored common decl_3 SI defer-output file a.f90 line
> > 5 col 0 size <integer_cst 0x7ffff7854988 32> unit size <integer_cst
> > 0x7ffff7854690 4>
> > align 128 context <function_decl 0x7ffff794b300 test> chain
> > <var_decl 0x7ffff794d0a0 i.1>>
> >
> > Are you suggesting we remove the entire code path here:
> >
> > /* Try harder to get a rtl. If this symbol ends up not being emitted
> > in the current CU, resolve_addr will remove the expression referencing
> > it. */
> >
> > ??
>
> Yes.
That will very much pessimize debug info. While we are now always in
-funit-at-a-time mode, that doesn't mean DECL_RTL is computed early enough.
>From the file scope non-static vars, at the point debug info is generated only
the first var usually has DECL_RTL set, all others don't.
For the cfgexpand.c occurence of this idiom, please see e.g. PR41353 -
even simple testcases like:
int i = 1, j, k = 1;
int
foo (void)
{
int i1 = 2 * i;
int i2 = 2 * i;
int k1 = 2 * k;
int k2 = 2 * k;
return j;
}
(and note this is artificial testcase, while obviously if the function does
something real, the same problem will be present often too) will have value
just for i1/i2, but not for k1/k2. i above has DECL_RTL set in
notice_global_symbol, but all other such vars have DECL_RTL set only way
after debuginfo for foo is created (unless the function has non-optimized
out references to the vars). As we can't create DECL_RTL just for -g case
and at different time for -g0, we do the DECL_RTL + SET_DECL_RTL NULL
hack.
Jakub
