Re: [PATCH] s390: Fix s390_const_int_pool_entry_p and movdi peephole2 [PR114605]

[Andreas Krebbel <krebbel@linux.ibm.com>]

On 4/8/24 13:43, Ilya Leoshkevich wrote:
> On Sat, 2024-04-06 at 18:58 +0200, Jakub Jelinek wrote:
>> Hi!
>>
>> The following testcase is miscompiled, because we have initially
>> a movti which loads the 0x3f8000003f800000ULL TImode constant
>> from constant pool.  Later on we split it into a pair of DImode
>> loads.  Now, for the first load (why just that?, though not stage4
>> material) we trigger the peephole2 which uses
>> s390_const_int_pool_entry_p.
>> That function doesn't check at all the constant pool mode though,
>> sees
>> the constant pool at that address has a CONST_INT value and just
>> assumes
>> that is the value to return, which is especially wrong for big-
>> endian,
>> if it is a DImode load from offset 0, it should be loading 0 rather
>> than
>> 0x3f8000003f800000ULL.
>> The following patch adds checks if we are extracing a MODE_INT mode,
>> if the constant pool has MODE_INT mode as well, punts if constant
>> pool
>> has smaller mode size than the extraction one (then it would be UB),
>> if it has the same mode as before keeps using what it did before,
>> if constant pool has a larger mode than the one being extracted, uses
>> simplify_subreg.  I'd have used avoid_constant_pool_reference
>> instead which can handle also offsets into the constant pool
>> constants,
>> but it can't handle UNSPEC_LTREF.
>>
>> Another thing is that once that is fixed, we ICE when we extract
>> constant
>> like 0, ior insn predicate require non-0 constant.  So, the patch
>> also
>> fixes the peephole2 so that if either 32-bit half is zero, it uses a
>> mere
>> load of the constant into register rather than a pair of such load
>> and ior.
>>
>> Bootstrapped/regtested on s390x-linux, ok for trunk?
> 
> Hi Jakub, thanks for the patch, it looks good to me.
> Since I'm not a maintainer, we need to wait for Andreas' opinion.

Ok. Thank you very much Jakub for fixing this!

Andreas

> 
>>
>> 2024-04-06  Jakub Jelinek  <jakub@redhat.com>
>>
>> 	PR target/114605
>> 	* config/s390/s390.cc (s390_const_int_pool_entry_p): Punt
>> 	if mem doesn't have MODE_INT mode, or pool constant doesn't
>> 	have MODE_INT mode, or if pool constant mode is smaller than
>> 	mem mode.  If mem mode is different from pool constant mode,
>> 	try to simplify subreg.  If that doesn't work, punt, if it
>> 	does, use the simplified constant instead of the constant
>> pool
>> 	constant.
>> 	* config/s390/s390.md (movdi from const pool peephole): If
>> 	either low or high 32-bit part is zero, just emit move insn
>> 	instead of move + ior.
>>
>> 	* gcc.dg/pr114605.c: New test.