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Date: Mon, 25 Aug 2014 11:24:00 -0000
From: Hans-Peter Nilsson <hp@bitrange.com>
To: Ilya Enkovich <enkovich.gnu@gmail.com>
cc: gcc-patches <gcc-patches@gcc.gnu.org>,     Evgeny Stupachenko <evstupac@gmail.com>
Subject: Re: Enable EBX for x86 in 32bits PIC code
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On Mon, 25 Aug 2014, Ilya Enkovich wrote:
> 2014-08-23 5:47 GMT+04:00 Hans-Peter Nilsson <hp@bitrange.com>:
> > ...did you send the right version of the patch?
> > This one uses the RTX-returning hook only in boolean tests,
> > unless I misread.

(I did, but not by much.)

> NULL returned by hook means we do not have implicit pic arg to
> pass/receive and there are pieces of code which should be executed
> only when implicit pic arg exists.  This causes these boolean tests.

Well, obviously, but...

> There are also non boolean usages. E.g.:

I thing singular ("usage") is more correct?
I saw only one such use. :)

> +      rtx old_reg = targetm.calls.implicit_pic_arg (fndecl);
> +      rtx new_reg = gen_reg_rtx (GET_MODE (old_reg));
> +      emit_move_insn (new_reg, old_reg);
> +      pic_offset_table_rtx = new_reg;

And before that, it's called as a boolean test, throwing away
the result!

I suggest you change the hook to return a boolean, with a
pointer argument to a variable to set, passed as NULL from
callers not interested in the actual value.

I.e. instead of:

> >> +@deftypefn {Target Hook} rtx TARGET_IMPLICIT_PIC_ARG (const_tree @var{fntype_or_decl})

make it a:

@deftypefn {Target Hook} bool TARGET_IMPLICIT_PIC_ARG
 (const_tree @var{fntype_or_decl}, rtx *@var{addr})

brgds, H-P