[PATCH] Fix PR71598, aliasing between enums and compatible types

[Christophe Lyon]

On Wed, 3 Apr 2019 at 10:24, Richard Biener <rguenther@suse.de> wrote:
>
> On Wed, 3 Apr 2019, Christophe Lyon wrote:
>
> > Hi!
> >
> > On Fri, 29 Mar 2019 at 20:02, Jeff Law <law@redhat.com> wrote:
> > >
> > > On 3/29/19 9:09 AM, Jason Merrill wrote:
> > > > On Fri, Mar 29, 2019 at 4:48 AM Richard Biener <rguenther@suse.de> wrote:
> > > >>
> > > >> On Thu, 28 Mar 2019, Jason Merrill wrote:
> > > >>
> > > >>> On 3/26/19 4:40 AM, Richard Biener wrote:
> > > >>>> On Mon, 18 Mar 2019, Richard Biener wrote:
> > > >>>>
> > > >>>>> On Fri, 15 Mar 2019, Jason Merrill wrote:
> > > >>>>>
> > > >>>>>> On 3/15/19 9:33 AM, Richard Biener wrote:
> > > >>>>>>>
> > > >>>>>>> The following is an attempt to fix PR71598 where C (and C++?) have
> > > >>>>>>> an implementation-defined compatible integer type for each enum
> > > >>>>>>> and the TBAA rules mandate that accesses using a compatible type
> > > >>>>>>> are allowed.
> > > >>>>>>
> > > >>>>>> This does not apply to C++; an enum does not alias its underlying type.
> > > >>>>>
> > > >>>>> Thus the following different patch, introducing c_get_alias_set and
> > > >>>>> only doing the special handling for C family frontends (I assume
> > > >>>>> that at least ObjC is also affected).
> > > >>>>>
> > > >>>>> Bootstrap & regtest running on x86_64-unknown-linux-gnu, OK?
> > > >>>>
> > > >>>> Ping.  Also consider the additional testcase below to be added.
> > > >>>>
> > > >>>> Richard.
> > > >>>>
> > > >>>> 2019-03-18  Richard Biener  <rguenther@suse.de>
> > > >>>>
> > > >>>>          PR c/71598
> > > >>>>          * gimple.c: Include langhooks.h.
> > > >>>>          (gimple_get_alias_set): Treat enumeral types as the underlying
> > > >>>>          integer type.
> > > >>>
> > > >>> Won't this affect all languages?
> > > >>
> > > >> It affects all languages during the LTO optimization phase, yes.
> > > >> There's unfortunately no way around that at the moment.
> > > >
> > > > Ah, well.  Looks good to me, then.
> > > Likewise.  And with Joseph largely offline right now, that's going to
> > > have to be sufficient :-)
> > >
> >
> >
> > I've noticed minor new errors at link time on arm with the 2 new testcases.
> > pr71598-1.c complains on arm-none-eabi because
> > arm-none-eabi/bin/ld: warning: /ccu5w26t.o uses 32-bit enums yet the
> > output is to use variable-size enums; use of enum values across
> > objects may fail
> >
> > conversely, pr71598-2.c complains on arm-none-linux-gnueabi* because:
> > arm-none-linux-gnueabi/bin/ld: warning: /ccl5OUKi.o uses variable-size
> > enums yet the output is to use 32-bit enums; use of enum values across
> > objects may fail
> >
> > In both cases this is because crt0.o is built with the opposite
> > (default) short-enum option than the testcase, so the linker sees a
> > mismatch between crt0.o and pr71598-X.o.
> >
> > Shall I add target-dependent dg-warning directives in the testcases,
> > or is there a better way?
>
> Maybe dg-skip the test for target_short_enums which seems to exist?
>
> Can you try if that works and if so, commit the fix?
>

Thanks, here is what I have committed as r270126.
(skip one test on short_enums targets, skip the other one on
non-short_enums targets)

Christophe

> Thanks,
> Richard.
-------------- next part --------------
2019-04-13  Christophe Lyon  <christophe.lyon@linaro.org>

	PR c/71598
	* gcc.dg/torture/pr71598-1.c: Skip if short_enums target.
	* gcc.dg/torture/pr71598-2.c: Skip if not short_enums target.

Index: gcc/testsuite/gcc.dg/torture/pr71598-1.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr71598-1.c	(revision 270125)
+++ gcc/testsuite/gcc.dg/torture/pr71598-1.c	(revision 270126)
@@ -1,4 +1,5 @@
 /* { dg-do run } */
+/* { dg-skip-if "" { short_enums } } */
 /* { dg-additional-options "-fno-short-enums" } */
 
 enum e1 { c1 };
Index: gcc/testsuite/gcc.dg/torture/pr71598-2.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr71598-2.c	(revision 270125)
+++ gcc/testsuite/gcc.dg/torture/pr71598-2.c	(revision 270126)
@@ -1,4 +1,5 @@
 /* { dg-do run } */
+/* { dg-skip-if "" { ! short_enums } } */
 /* { dg-additional-options "-fshort-enums" } */
 
 enum e1 { c1 = -__INT_MAX__ };