On Sun, Nov 20, 2016 at 10:00 PM, Uros Bizjak <ubiz...@gmail.com> wrote:
>>> This also eliminate quite a few zero-extensions in the compile.exp testsuite
>>> at -O2 on the SPARC. Tested on x86-64/Linux and SPARC/Solaris.
>>>
>>>
>>> 2016-11-07 Eric Botcazou <ebotca...@adacore.com>
>>>
>>> PR rtl-optimization/59461
>>> * doc/rtl.texi (paradoxical subregs): Add missing word.
>>> * combine.c (reg_nonzero_bits_for_combine): Do not discard results
>>> in modes with precision larger than that of last_set_mode.
>>> * rtlanal.c (nonzero_bits1) <SUBREG>: If WORD_REGISTER_OPERATIONS is
>>> set and LOAD_EXTEND_OP is appropriate, propagate results from inner
>>> REGs to paradoxical SUBREGs.
>>> (num_sign_bit_copies1) <SUBREG>: Likewise. Check that the mode is not
>>> larger than a word before invoking LOAD_EXTEND_OP on it.
>>
>> I have installed it after testing on ARM/EABI and IA-64/Linux.
>
> Just a heads-up for now, the above patch introduced following
> testsuite failures on Alpha [1]:
>
> FAIL: gcc.dg/atomic/stdatomic-compare-exchange-1.c -O2 execution test
> FAIL: gcc.dg/atomic/stdatomic-compare-exchange-1.c -O3 -g execution test
> FAIL: gcc.dg/atomic/stdatomic-compare-exchange-1.c -O2 -flto
> -fno-use-linker-plugin -flto-partition=none execution test
> FAIL: gcc.dg/atomic/stdatomic-compare-exchange-1.c -O2 -flto
> -fuse-linker-plugin -fno-fat-lto-objects execution test
> FAIL: gcc.dg/atomic/stdatomic-compare-exchange-2.c -O2 execution test
> FAIL: gcc.dg/atomic/stdatomic-compare-exchange-2.c -O3 -g execution test
> FAIL: gcc.dg/atomic/stdatomic-compare-exchange-2.c -O2 -flto
> -fno-use-linker-plugin -flto-partition=none execution test
> FAIL: gcc.dg/atomic/stdatomic-compare-exchange-2.c -O2 -flto
> -fuse-linker-plugin -fno-fat-lto-objects execution test
>
> On a first look, it looks that something is wrong with sign-extensions.
>
> I will try to look into this a bit more.
Your patch exposes a problem in the ree pass where:
50: $22:QI=$8:QI
REG_EQUAL [`expected']
43: [$2:DI+low(`expected')]=$8:QI
51: $3:DI=sign_extend($22:QI)
gets converted to:
50: $3:DI=sign_extend($8:QI)
141: $22:DI=$3:DI
43: [$2:DI+low(`expected')]=$8:QI
$22:DI is used later in a fallthrough block, and the above sequences
are certainly not equal wrt. to $22. The first one does have all high
bits of $22 zero, the second one doesn't.
-fno-ree fixes the failures.
I will fill a PR tomorrow.
Uros.
