On Fri, Nov 30, 2012 at 3:51 PM, Steven Bosscher <stevenb.gcc@gmail.com> wrote:

>>>>> This one-liner causes following runtime test failure [1] for
>>>>> alphaev68-linux-gnu:
>>>>>
>>>>> FAIL: gfortran.fortran-torture/execute/save_1.f90 execution,  -O2
>>>>> FAIL: gfortran.fortran-torture/execute/save_1.f90 execution,  -O2
>>>>> -fomit-frame-pointer -finline-functions
>>>>> FAIL: gfortran.fortran-torture/execute/save_1.f90 execution,  -O2
>>>>> -fomit-frame-pointer -finline-functions -funroll-loops
>>>>> FAIL: gfortran.fortran-torture/execute/save_1.f90 execution,  -O2
>>>>> -fbounds-check
>>>>>
>>>>> The patch miscompiles libgfortran library.
>>>>>
>>>>> I will provide more info tomorrow, any hint what/where should I look
>>>>> for differences?
>>>>
>>>> Anywhere.  The bug disabled a large part of alias analysis.
>>>>
>>>> Perhaps you can bisect it and backport the fix along the steps.
>>>
>>> Or open a PR and assign it to me, ultimately I'm responsible for this breakage.
>>
>> I have found the problem. Luckily, it is the testcase that is
>> miscompiled. The problem is in sched1 pass that moves write to an
>> address "addrX" that happens to be aliased with AND mutilated address
>> "addrY & -7". The improved alias analysis does not notice that the
>> write is inside (addr & -7) region, allowing write to be moved after
>> read.
>
> Based on this description of the problem, I remembered these patches
> from Alexandre:
>
> 2012-07-06  Alexandre Oilva  <>
>
>         PR rtl-optimization/53827
>         PR debug/53671
>         PR debug/49888
>         * alias.c (memrefs_conflict_p): Adjust offset and size by the
>         same amount for alignment ANDs.
>
> 2012-06-21  Alexandre Oliva  <>
>
>         PR debug/53671
>         PR debug/49888
>         * alias.c (memrefs_conflict_p): Improve handling of AND for alignment.
>
>
> They are r188868 and r189325. Can you try revert these and see if that
> fixes your problem (probably at the expense of some other problem
> returning, but at least it'd be a good place to start looking
> further...).

Yes backing out these revisions with attached patch fixes the runtime failure!

Uros.