Re: [shrink-wrap] should not sink instructions which may cause trap ?

[Jiong Wang <jiong dot wang at arm dot com>]

On 26/09/14 17:12, Jeff Law wrote:
> On 09/26/14 08:50, Jiong Wang wrote:
>
> > > > >      if (may_trap_p (x))
> > > > >        don't sink this instruction.
> > > > >
> > > > >       any comments?
> > > > Should be checking if x may throw internally instead.
> > > Richard, thanks for the suggestion, have used insn_could_throw_p to do
> > > the check,
> > > which will only do the check when flag_exception and
> > > flag_non_call_exception be true,
> > > so those instruction could still be sink for normal c/c++ program.
> > >
> > > Jeff,
> > >
> > >      below is the fix for pr49847.C regression on aarch64. I re-run
> > > full test on
> > >      aarch64-none-elf bare metal, no regression.
> > >
> > >      bootstrap ok on x86, no regression on check-gcc/g++.
> > >
> > >      ok for trunk?
> > (re-sent with changelog entry)
> >
> > gcc/
> >
> > 2014-09-26  Jiong Wang<jiong.wang@arm.com>
> >
> >           * shrink-wrap.c (move_insn_for_shrink_wrap): Check
> > "insn_could_throw_p" before
> >           sinking insn.
> I think can_throw_internal, per Richi's recommendation is better.
>
> Note that can_throw_internal keys off the existence of the EH landing
> pads for the particular insn.
>
> If flag_exceptions is false (for example), then would not expect those
> landing pads to exist and the insn would not be considered as
> potentially throwing.
>
> Can you test with can_throw_internal to verify it's behaviour and resubmit

thanks for pointing this out, patch updated.

re-tested, pass x86-64 bootstrap and no regression on check-gcc/g++.
pass aarch64-none-elf cross check also.

ok for trunk?

BTW, another bug exposed by linux x86-64 kernel build, and it's at

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63404

the problem is caused by we missed clobber/use check. I will send
a seperate patch for review. really sorry for causing the trouble,
the insn move in generic code is actually not that generic, related
with some backend features...

2014-09-26  Jiong Wang  <jiong.wang@arm.com>

        * shrink-wrap.c (move_insn_for_shrink_wrap): Check "can_throw_internal" before
        sinking insn.

commit bff6072abd52fecde5916d1967a7833f581c1e98
Author: Jiong Wang <jiong.wang@arm.com>
Date:   Mon Sep 29 13:32:02 2014 +0100

    1

diff --git a/gcc/shrink-wrap.c b/gcc/shrink-wrap.c
index bd4813c..b1ff8a2 100644
--- a/gcc/shrink-wrap.c
+++ b/gcc/shrink-wrap.c
@@ -189,6 +189,9 @@ move_insn_for_shrink_wrap (basic_block bb, rtx_insn *insn,
       unsigned int nonconstobj_num = 0;
       rtx src_inner = NULL_RTX;
 
+      if (can_throw_internal (insn))
+	return false;
+
       subrtx_var_iterator::array_type array;
       FOR_EACH_SUBRTX_VAR (iter, array, src, ALL)
 	{