Patchwork [Fortran] PR 50163 - ICE with nonconst expr in init expr

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Submitter Tobias Burnus
Date Aug. 23, 2011, 12:26 p.m.
Message ID <4E539C93.7070704@net-b.de>
Download mbox | patch
Permalink /patch/111081/
State New
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Comments

Tobias Burnus - Aug. 23, 2011, 12:26 p.m.
The bug is a regression: An error was printed with 4.1.x but since 4.3.x 
one gets an ICE. [No idea what GCC 4.2 does.] The solution is simply: 
Returning if there is a MATCH_ERROR.

See PR (esp. comment 2) for a more detailed description:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50163#c0

Build and regtested on x86-64-linux.
OK for the trunk? And to which version should it be backported? Only 
4.6? Also 4.5? Or even 4.4?

Tobias
Mikael Morin - Aug. 24, 2011, 10:12 a.m.
On Tuesday 23 August 2011 14:26:59 Tobias Burnus wrote:
> The bug is a regression: An error was printed with 4.1.x but since 4.3.x
> one gets an ICE. [No idea what GCC 4.2 does.] The solution is simply:
> Returning if there is a MATCH_ERROR.
> 
> See PR (esp. comment 2) for a more detailed description:
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50163#c0
> 
> Build and regtested on x86-64-linux.
> OK for the trunk?
OK.

> And to which version should it be backported? Only
> 4.6? Also 4.5? Or even 4.4?
I have no strong opinion about it; I would say 4.6 and 4.5. 
If you want 4.4 too.

Isn't there some rules about backporting? The way we do it now, it looks 
completely arbitrary.

Mikael
Tobias Burnus - Aug. 24, 2011, 1:31 p.m.
On 08/24/2011 12:12 PM, Mikael Morin wrote:
> On Tuesday 23 August 2011 14:26:59 Tobias Burnus wrote:
>> OK for the trunk?
> OK.

Thanks for the review! Committed to the 4.7 trunk (Rev. 178038); I will 
backport the patch later. (For cross-readers: That's a patch for a 4.3+ 
ice-on-invalid-code regression.)


> Isn't there some rules about backporting? The way we do it now, it 
> looks completely arbitrary.

I think it *is* arbitrary - and unavoidable so.

The main idea behind regression fixing is to make sure that what once 
worked should continue to work. But what always had been broken can 
remain broken and will be only fixed on the trunk.  Reason: If you fix 
more, the behaviour on the branch changes and you may introduce 
regressions. If thinks are known to be broken, you can simply work 
around them.

Additional ingredients are: How serious is the problem? A wrong-code 
issue occurring in a potentially often used part has a different 
priority than an accepts-invalid or ice-on-invalid-code issue. Also, a 
patch which is huge is less suited than a small "trivial" patch. 
Regressions, which existed for a long time are typically also less 
important - otherwise they would have been fixed or found before.

But there are also other items such as: Which is the last maintained 
version in GCC, which versions are still being used (such that it makes 
sense to backport), and which patches (Linux) distributions want to see. 
Additionally, as backporting takes time (bootstrap, regtesting, and 
maybe even adapting the patch slightly): How much time wants the 
developer spend on backporting.

My impression is that gfortran is currently doing too much 
non-regression backporting, which should be left to serious ICE-on-valid 
code and wrong-code issues. Especially as older versions do not see as 
much testing as the trunk.

On the other hand, backporting simple fixes to regressions or really bad 
wrong-code issues (which we hadn't for a while) down to 4.4 should be 
also fine.

I think every modern (= F2003) developer can relatively simply update to 
4.6 or the trunk. The older versions are mostly for those using the 
default compiler of the system; those typically only need some Fortran 
77/90 compiler, for which the older versions (4.4 or 4.5) should be fine.

But at the end it is question of style. That's similar to Linux 
distributions. I think Jakub/Red Hat ports many patches (bug fixes but 
also features) back to their old versions, while for instance 
Richard/SUSE's package has only few patches and essentially grabs the 
current branch. Both approaches makes sense and either one has 
advantages and disadvantages.

I think we should try extra hard to avoid regressions on the branches 
and mostly concentrate on the trunk, but we can still backport one patch 
or the other to the branches.

I didn't really answer your question, did I?

Tobias
Mikael Morin - Aug. 25, 2011, 1:40 p.m.
On Wednesday 24 August 2011 15:31:17 Tobias Burnus wrote:
> > Isn't there some rules about backporting? The way we do it now, it
> > looks completely arbitrary.
> 
> I think it *is* arbitrary - and unavoidable so.
> 
> The main idea behind regression fixing is to make sure that what once
> worked should continue to work. But what always had been broken can
> remain broken and will be only fixed on the trunk.  Reason: If you fix
> more, the behaviour on the branch changes and you may introduce
> regressions. If thinks are known to be broken, you can simply work
> around them.
> 
> Additional ingredients are: How serious is the problem? A wrong-code
> issue occurring in a potentially often used part has a different
> priority than an accepts-invalid or ice-on-invalid-code issue. Also, a
> patch which is huge is less suited than a small "trivial" patch.
> Regressions, which existed for a long time are typically also less
> important - otherwise they would have been fixed or found before.
> 
> But there are also other items such as: Which is the last maintained
> version in GCC, which versions are still being used (such that it makes
> sense to backport), and which patches (Linux) distributions want to see.
> Additionally, as backporting takes time (bootstrap, regtesting, and
> maybe even adapting the patch slightly): How much time wants the
> developer spend on backporting.
> 
OK, it's a complex problem, and that's the very reason for my remark.

> My impression is that gfortran is currently doing too much
> non-regression backporting, which should be left to serious ICE-on-valid
> code and wrong-code issues. Especially as older versions do not see as
> much testing as the trunk.
> 
I didn't have that impression; a matter of style probably.
Yes we could try to be more carefull in the future.

> [...]
> 
> But at the end it is question of style. 
> [...]
> 
Well, I was asking whether we could decide on our own style.

> [...]
> 
> I didn't really answer your question, did I?
> 
You exposed your point of view clearly, which is certainly a step forward.

There are some basic rules for backports, on which everybody agrees; but in 
the end the same question is raised over and over again, and nobody seems to 
know really: how far should we backport?

Currently the GCC rules are (basically):
not a regression -> no backport (unless serious bug/trivial fix)
regression -> backport

On the other hand, we have three open branches (trunk apart) and it is not 
clear to me whether we should apply the same rules to all of them or shade the 
seriousness and trivialness trigger levels into the 3 levels of backport we 
have.
Furthermore we have to take into account our (lack of) ressources and (amount 
of) interest for doing the backport.

So I was proposing to include version numbers into the rules, and be more 
specific about them, like for example:
  - Serious (wrong-code, ice-on-valid) non-regression bugs with a simple fix 
are backported to N-1 only. [N is trunk]
  - Non-serious regressions are not backported beyond N-2.
  - ...

Of course in the end, what is simple, what is serious, are arbitrary.
Maybe you are right, it's unavoidable.

Mikael

Patch

2011-08-23  Tobias Burnus  <burnus@net-b.de>

	PR fortran/50163
	* check_init_expr (check_init_expr): Return when an error occured.

2011-08-23  Tobias Burnus  <burnus@net-b.de>

	PR fortran/50163
	* gfortran.dg/initialization_28.f90: New.

diff --git a/gcc/fortran/expr.c b/gcc/fortran/expr.c
index 9922094..b050b11 100644
--- a/gcc/fortran/expr.c
+++ b/gcc/fortran/expr.c
@@ -2481,6 +2481,9 @@  check_init_expr (gfc_expr *e)
 	    m = MATCH_ERROR;
 	  }
 
+	if (m == MATCH_ERROR)
+	  return FAILURE;
+
 	/* Try to scalarize an elemental intrinsic function that has an
 	   array argument.  */
 	isym = gfc_find_function (e->symtree->n.sym->name);
--- /dev/null	2011-08-23 07:28:57.751883742 +0200
+++ gcc/gcc/testsuite/gfortran.dg/initialization_28.f90	2011-08-23 14:02:02.000000000 +0200
@@ -0,0 +1,9 @@ 
+! { dg-do compile }
+!
+! PR fortran/50163
+!
+! Contributed by Philip Mason
+!
+character(len=2) :: xx ='aa'
+integer :: iloc=index(xx,'bb') ! { dg-error "has not been declared or is a variable" }
+end