On Tue, Mar 01, 2016 at 10:21:27AM +0100, Richard Biener wrote:
> On Mon, 29 Feb 2016, James Greenhalgh wrote:
>
> > On Fri, Feb 26, 2016 at 09:32:53AM +0100, Richard Biener wrote:
> > >
> > > The following fixes PR69951, hopefully the last case of decl alias
> > > issues with alias analysis. This time it's points-to and the DECL_UIDs
> > > used in points-to sets not being canonicalized.
> > >
> > > The simplest (and cheapest) fix is to make aliases refer to the
> > > ultimate alias target via their DECL_PT_UID which we conveniently
> > > have available.
> > >
> > > Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
> > >
> > > Richard.
> > >
> > > 2016-02-26 Richard Biener <rguent...@suse.de>
> > >
> > > PR tree-optimization/69551
> > > * tree-ssa-structalias.c (get_constraint_for_ssa_var): When
> > > looking through aliases adjust DECL_PT_UID to refer to the
> > > ultimate alias target.
> > >
> > > * gcc.dg/torture/pr69951.c: New testcase.
> >
> > I see this new testcase failing on an ARM target as so:
> >
> > /tmp/ccChjoFc.s: Assembler messages:
> > /tmp/ccChjoFc.s:21: Warning: [-mwarn-syms]: Assignment makes a symbol
> > match an ARM instruction: b
> >
> > FAIL: gcc.dg/torture/pr69951.c -O0 (test for excess errors)
> >
> > But I haven't managed to reproduce it outside of the test environment.
> >
> > The fix looks trivial, rename b to anything else you fancy (well... stay
> > clear of add and ldr). I'll put a fix in myself if I can manage to get
> > this to reproduce - though if anyone else wants to do it I won't be
> > offended :-).
>
> Huh, I wonder what's the use of such warning. After all 'ldr' is a valid
> C symbol name, too. In fact my cross arm as doesn't report this
> warning (binutils 2.25.0)
>
> > arm-suse-linux-gnueabi-as t.s -mwarn-syms
> Assembler messages:
> Error: unrecognized option -mwarn-syms
Right, I've figured out the set of conditions... You need to be targeting
an arm-*-linux-* system to make sure that the ASM_OUTPUT_DEF definition
from config/arm/linux-elf.h is pulled in. This causes us to emit:
b = a
Rather than
.set b,a
Writing it as "b = a" causes the warning added to resolve binutils
PR18347 [1] to kick in, so you need binutils > 2.26 or to have backported
that patch).
Resolving it by hacking the testcase would be one fix, but I wonder why the
ARM port prefers to emit "b = a" in a linux environment if .set does the
same thing and always avoids the warning? Maybe Ramana/Richard/Kyrill/Nick
remember? (AArch64 does the same thing, but the AArch64 gas port doesn't
have the PR18347 fix).
Cheers,
James
---
[1]: https://sourceware.org/bugzilla/show_bug.cgi?id=18347
>
> Richard.
>
