Re: ipa-visibility TLC 2/n

[David Edelsohn <dje.gcc@gmail.com>]

Honza,

How can we make further progress with the large regression on AIX?

Thanks, David

On Fri, May 30, 2014 at 1:24 PM, David Edelsohn <dje.gcc@gmail.com> wrote:
> Honza,
>
> For example g++.dg/abi/vcall1.C fails at a call in a "localalias"
> function, which jumps to a bad location:
>
>
> (gdb) up
> #1  0x100004c0 in B::B() [clone .localalias.2] ()
> (gdb) x/16i $pc-32
>    0x100004a0 <_ZN1BC2Ev+156>:  add     r10,r10,r8
>    0x100004a4 <_ZN1BC2Ev+160>:  mr      r3,r10
>    0x100004a8 <_ZN1BC2Ev+164>:  stw     r2,20(r1)
>    0x100004ac <_ZN1BC2Ev+168>:  lwz     r10,0(r9)
>    0x100004b0 <_ZN1BC2Ev+172>:  lwz     r11,8(r9)
>    0x100004b4 <_ZN1BC2Ev+176>:  mtctr   r10
>    0x100004b8 <_ZN1BC2Ev.localalias.2+180>:     lwz     r2,4(r9)
>    0x100004bc <_ZN1BC2Ev.localalias.2+184>:     bctrl
> => 0x100004c0 <_ZN1BC2Ev.localalias.2+188>:     lwz     r2,20(r1)
>    0x100004c4 <_ZN1BC2Ev.localalias.2+192>:     addi    r1,r31,64
>    0x100004c8 <_ZN1BC2Ev.localalias.2+196>:     lwz     r0,8(r1)
>    0x100004cc <_ZN1BC2Ev.localalias.2+200>:     mtlr    r0
>    0x100004d0 <_ZN1BC2Ev.localalias.2+204>:     lwz     r31,-4(r1)
>    0x100004d4 <_ZN1BC2Ev.localalias.2+208>:     blr
>
>
>
> On Fri, May 30, 2014 at 3:20 AM, Richard Sandiford
> <rdsandiford@googlemail.com> wrote:
>> Jan Hubicka <hubicka@ucw.cz> writes:
>>>> Jan Hubicka <hubicka@ucw.cz> writes:
>>>> >> Richard Sandiford wrote the original section anchors implementation,
>>>> >> so he would be a good person to comment about the interaction between
>>>> >> aliases and section anchors.
>>>> >
>>>> > Thanks! Richard, does this patch seem sane?
>>>>
>>>> Looks good to me in principle, but with:
>>>>
>>>> > +      struct symtab_node *snode;
>>>> >        decl = SYMBOL_REF_DECL (symbol);
>>>> > +
>>>> > +      snode = symtab_node (decl);
>>>> > +      if (snode->alias)
>>>> > +       {
>>>> > + rtx target = DECL_RTL (symtab_alias_ultimate_target
>>>> > (snode)->decl);
>>>> > + SYMBOL_REF_BLOCK_OFFSET (symbol) = SYMBOL_REF_BLOCK_OFFSET
>>>> > (target);
>>>> > +         return;
>>>> > +       }
>>>>
>>>> is SYMBOL_REF_BLOCK_OFFSET (target) guaranteed to be valid at this point?
>>>> It looked at face value like you'd need a recursive call to place_block_symbol
>>>> on the target before the copy.
>>>
>>> My reading was that SYMBOL_REF_BLOCK_OFFSET is computed at DECL_RTL
>>> calculation time. But you are right - it is done by validize_mem that
>>> is not done by DECL_RTL.  Shall I just call it on target first?
>>
>> Yeah, sounds like calling place_block_symbol would be safer.
>>
>> IIRC, the reason I didn't do it at SET_DECL_RTL time is that some frontends
>> tended to create placeholder decls that for whatever reason ended up with
>> an initial DECL_RTL, then changed the properties of the decl later once
>> more information was known.  (This was all many years ago.)
>>
>> Thanks,
>> Richard