Re: [PATCH] [RFC] PR target/52813 and target/11807

[Christophe Lyon <christophe.lyon@linaro.org>]

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On Fri, 11 Jan 2019 at 23:59, Jeff Law <law@redhat.com> wrote:
>
> On 1/8/19 5:03 AM, Richard Sandiford wrote:
> > Bernd Edlinger <bernd.edlinger@hotmail.de> writes:
> >> On 1/7/19 10:23 AM, Jakub Jelinek wrote:
> >>> On Sun, Dec 16, 2018 at 06:13:57PM +0200, Dimitar Dimitrov wrote:
> >>>> -  /* Clobbering the STACK POINTER register is an error.  */
> >>>> +  /* Clobbered STACK POINTER register is not saved/restored by GCC,
> >>>> +     which is often unexpected by users.  See PR52813.  */
> >>>>    if (overlaps_hard_reg_set_p (regset, Pmode, STACK_POINTER_REGNUM))
> >>>>      {
> >>>> -      error ("Stack Pointer register clobbered by %qs in %<asm%>", regname);
> >>>> +      warning (0, "Stack Pointer register clobbered by %qs in %<asm%>",
> >>>> +         regname);
> >>>> +      warning (0, "GCC has always ignored Stack Pointer %<asm%> clobbers");
> >>>
> >>> Why do we write Stack Pointer rather than stack pointer?  That is really
> >>> weird.  The second warning would be a note based on the first one, i.e.
> >>> if (warning ()) note ();
> >>> and better have some -W* option to silence the warning.
> >>>
> >>
> >> Yes, thanks for this suggestion.
> >>
> >> Meanwhile I found out, that the stack clobber has only been ignored up to
> >> gcc-5 (at least with lra targets, not really sure about reload targets).
> >> From gcc-6 on, with the exception of PR arm/77904 which was a regression due
> >> to the underlying lra change, but fixed later, and back-ported to gcc-6.3.0,
> >> this works for all targets I tried so far.
> >>
> >> To me, it starts to look like a rather unique and useful feature, that I would
> >> like to keep working.
> >
> > Not sure what you mean by "unique".  But forcing a frame is a bit of
> > a slippery concept.  Force it where?  For the asm only, or the whole
> > function?  This depends on optimisation and hasn't been consistent
> > across GCC versions, since it depends on the shrink-wrapping
> > optimisation.  (There was a similar controversy a while ago about
> > to what extent -fno-omit-frame-pointer should "force a frame".)
> >
> > The effect on the redzone seems like something that should be specified
> > explicitly rather than as an (accidental?) side effect of listing the
> > sp in the clobber list.  Maybe this would be another use for the "asm
> > attributes" proposal.  "noreturn" was another attribute suggested on
> > IRC yesterday.
> >
> > But either way, the general feeling seems to be that going straight to a
> > hard error is too harsh, since there's quite a bit of existing code that
> > has the clobber.  This patch implements the compromise discussed on IRC
> > yesterday of making it a -Wdeprecated warning instead.
> >
> > Tested on x86_64-linux-gnu and aarch64-linux-gnu.  OK to install?
> >
> > Richard
> >
> > Dimitar: sorry the run-around on this patch, and thanks for the
> > submission.  It looks from all the controversy like it was a
> > long-festering PR for a reason. :-/
> >
> >
> > 2019-01-07  Richard Sandiford  <richard.sandiford@arm.com>
> >
> > gcc/
> >       PR inline-asm/52813
> >       * doc/extend.texi: Document that listing the stack pointer in the
> >       clobber list of an asm is a deprecated feature.
> >       * common.opt (Wdeprecated): Moved from c-family/c.opt.
> >       * cfgexpand.c (asm_clobber_reg_is_valid): Issue a -Wdeprecated
> >       warning instead of an error for clobbers of the stack pointer.
> >       Add a note explaining why.
> >
> > gcc/c-family/
> >       PR inline-asm/52813
> >       * c.opt (Wdeprecated): Move documentation and variable to common.opt.
> >
> > gcc/d/
> >       PR inline-asm/52813
> >       * lang.opt (Wdeprecated): Reference common.opt instead of c.opt.
> >
> > gcc/testsuite/
> >       PR inline-asm/52813
> >       * gcc.target/i386/pr52813.c (test1): Turn the diagnostic into a
> >       -Wdeprecated warning and expect a following note:.
> OK.
>
> FWIW the number of packages affected in Fedora was in single digits,
> some of which have already been fixed.
>
> But if folks want to go with a deprecated warning instead of straight to
> an error, I won't complain.
>
> jeff


Hi,

I originally complained because the arm test for pr77904.c was failing.
Since Richard's change that test emits a warning rather than an error,
but still fails. This small patch adds the missing dg-warning.

OK?

Thanks,

Christophe

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2019-01-17  Christophe Lyon  <christophe.lyon@linaro.org>

	* gcc.target/arm/pr77904.c: Add dg-warning for sp clobber.


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diff --git a/gcc/testsuite/gcc.target/arm/pr77904.c b/gcc/testsuite/gcc.target/arm/pr77904.c
index 76728c0..f279ec8 100644
--- a/gcc/testsuite/gcc.target/arm/pr77904.c
+++ b/gcc/testsuite/gcc.target/arm/pr77904.c
@@ -4,7 +4,8 @@
 __attribute__ ((noinline, noclone)) void
 clobber_sp (void)
 {
-  __asm volatile ("" : : : "sp");
+  __asm volatile ("" : : : "sp"); /* { dg-warning "listing the stack pointer register 'sp' in a clobber list is deprecated" } */
+
 }
 
 int