https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88233
Bug ID: 88233
Summary: combine fails to merge insns leaving unneeded reg
copies
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: bergner at gcc dot gnu.org
Target Milestone: ---
bergner@pike:~/gcc/BUGS/PR69493$ cat test.i
typedef struct { double a[2]; } A;
A
foo (const A *a)
{
return *a;
}
bergner@pike:~$ .../xgcc -B.../gcc -O2 -S test.i
bergner@pike:~$ cat test.s
ld 10,0(3)
ld 11,8(3)
mtvsrd 1,10
mtvsrd 2,11
blr
Entering combine, we have the following rtl:
...
insn 6 3 9 2 (set (reg:TI 121 [ D.2829 ])
(mem:TI (reg/v/f:DI 124 [ aD.2825 ]) [1 *a_2(D)+0 S16 A64]))
"test.i":5:10 1048 {*vsx_le_perm_load_ti}
(expr_list:REG_DEAD (reg/v/f:DI 124 [ aD.2825 ])
(nil)))
(insn 9 6 10 2 (set (reg:DF 122 [ <retval> ])
(subreg:DF (reg:TI 121 [ D.2829 ]) 0)) "test.i":5:10 515
{*movdf_hardfloat64}
(nil))
(insn 10 9 14 2 (set (reg:DF 123 [ <retval>+8 ])
(subreg:DF (reg:TI 121 [ D.2829 ]) 8)) "test.i":5:10 515
{*movdf_hardfloat64}
(expr_list:REG_DEAD (reg:TI 121 [ D.2829 ])
(nil)))
...
Combine should be able to merge insn 6 with both insn 9 and insn 10 to produce:
(insn ... (set (reg:DF 122)
(mem:DF (reg:DI 124))
(insn ... (set (reg:DF 123)
(mem:DF (plus:DI (reg:DI 124)
(const_int 8)))
By not merging them, we end up with two unneeded register copies we cannot
remove.
