https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94516
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |law at gcc dot gnu.org
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So, I see there actually two separate undesirable changes. One is that during
reload_cse_regs_1 because of the cselib.c changes it optimized 3 times:
-(insn 22 21 24 2 (parallel [
- (set (reg/f:DI 7 sp)
- (plus:DI (reg/f:DI 7 sp)
- (const_int 32 [0x20])))
- (clobber (reg:CC 17 flags))
- ]) "pr94516.c":6747:2 186 {*adddi_1}
- (expr_list:REG_ARGS_SIZE (const_int 0 [0])
- (nil)))
+(insn 22 21 24 2 (parallel [
+ (set (reg/f:DI 7 sp)
+ (reg/f:DI 40 r12 [84]))
+ ]) "pr94516.c":6747:2 66 {*movdi_internal}
+ (expr_list:REG_ARGS_SIZE (const_int 0 [0])
+ (nil)))
That in itself isn't a wrong-code change, the question is if it is actually
beneficial (maybe for -Os it could).
The second change happens in the reload_cse_move2add
/* Try to transform (set (REGX) (REGY))
(set (REGX) (PLUS (REGX) (CONST_INT A)))
...
(set (REGX) (REGY))
(set (REGX) (PLUS (REGX) (CONST_INT B)))
to
(set (REGX) (REGY))
(set (REGX) (PLUS (REGX) (CONST_INT A)))
...
(set (REGX) (plus (REGX) (CONST_INT B-A)))
*/
transformation, where REGX is sp and REGY is this r12 register that happens to
contain a copy of rsp with REG_ARGS_SIZE of 0 and this one is the wrong-code
one, because it ignores the fact that REGX is used in various other
instructions in between.
