Re: [PATCH] PR combine/110867 Fix narrow comparison of memory and constant

[Jeff Law <jeffreyalaw@gmail.com>]

On 8/2/23 07:49, Stefan Schulze Frielinghaus via Gcc-patches wrote:
> In certain cases a constant may not fit into the mode used to perform a
> comparison.  This may be the case for sign-extended constants which are
> used during an unsigned comparison as e.g. in
> 
> (set (reg:CC 100 cc)
>      (compare:CC (mem:SI (reg/v/f:SI 115 [ a ]) [1 *a_4(D)+0 S4 A64])
>          (const_int -2147483648 [0xffffffff80000000])))
> 
> Fixed by ensuring that the constant fits into comparison mode.
> 
> Furthermore, on some targets as e.g. sparc the constant used in a
> comparison is chopped off before combine which leads to failing test
> cases (see PR 110869).  Fixed by not requiring that the source mode has
> to be DImode, and excluding sparc from the last two test cases entirely
> since there the constant cannot be further reduced.
> 
> According to PR 110867 and 110869 this patch resolves bootstrap problems
> on armv8l and sparc.  While writing this, bootstrap+regtest are still
> running on x64 and s390x.  Assuming they pass, ok for mainline?
> 
> gcc/ChangeLog:
> 
> 	PR combine/110867
> 	* combine.cc (simplify_compare_const): Try the optimization only
> 	in case the constant fits into the comparison mode.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR combine/110869
> 	* gcc.dg/cmp-mem-const-1.c: Relax mode for constant.
> 	* gcc.dg/cmp-mem-const-2.c: Relax mode for constant.
> 	* gcc.dg/cmp-mem-const-3.c: Relax mode for constant.
> 	* gcc.dg/cmp-mem-const-4.c: Relax mode for constant.
> 	* gcc.dg/cmp-mem-const-5.c: Exclude sparc since here the
> 	constant is already reduced.
> 	* gcc.dg/cmp-mem-const-6.c: Exclude sparc since here the
> 	constant is already reduced.
OK
jeff