https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66812
--- Comment #5 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
(In reply to David Malcolm from comment #4)
> Created attachment 35946 [details]
> Equivalent C code
>
> (generated using gcc_jit_context_dump_to_file and lightly editing until
> valid C)
Compiling this with trunk with -O3 *doesn't* show the fre1 issue exhibited by
libgccjit; dump from cc1's fre1 looks like this:
;; Function test_pr66812 (test_pr66812, funcdef_no=0, decl_uid=1762,
cgraph_uid=0, symbol_order=0)
Setting value number of .MEM_3(D) to .MEM_3(D) (changed)
Value numbering .MEM_4 stmt = MEM[(struct value *)arr_1(D) +
16B].union_field.i_field = 0;
RHS 0 simplified to 0
No store match
Value numbering store MEM[(struct value *)arr_1(D) + 16B].union_field.i_field
to 0
Setting value number of .MEM_4 to .MEM_4 (changed)
Value numbering .MEM_6 stmt = MEM[(struct value *)arr_1(D) + 16B].type_code =
0;
RHS 0 simplified to 0
No store match
Value numbering store MEM[(struct value *)arr_1(D) + 16B].type_code to 0
Setting value number of .MEM_6 to .MEM_6 (changed)
Value numbering .MEM_8 stmt = MEM[(struct value *)arr_1(D) +
16B].union_field.ll_field = 10;
RHS 10 simplified to 10
No store match
Value numbering store MEM[(struct value *)arr_1(D) + 16B].union_field.ll_field
to 10
Setting value number of .MEM_8 to .MEM_8 (changed)
Value numbering .MEM_10 stmt = MEM[(struct value *)arr_1(D) + 16B].type_code =
19;
RHS 19 simplified to 19
No store match
Value numbering store MEM[(struct value *)arr_1(D) + 16B].type_code to 19
Setting value number of .MEM_10 to .MEM_10 (changed)
Value numbering .MEM_12 stmt = MEM[(struct value *)arr_1(D) +
16B].union_field.i_field = 0;
RHS 0 simplified to 0
No store match
Value numbering store MEM[(struct value *)arr_1(D) + 16B].union_field.i_field
to 0
Setting value number of .MEM_12 to .MEM_12 (changed)
Value numbering .MEM_14 stmt = MEM[(struct value *)arr_1(D) + 16B].type_code =
0;
RHS 0 simplified to 0
No store match
Value numbering store MEM[(struct value *)arr_1(D) + 16B].type_code to 0
Setting value number of .MEM_14 to .MEM_14 (changed)
Value numbers:
test_pr66812 (struct value * arr)
{
<bb 2>:
MEM[(struct value *)arr_1(D) + 16B].union_field.i_field = 0;
MEM[(struct value *)arr_1(D) + 16B].type_code = 0;
MEM[(struct value *)arr_1(D) + 16B].union_field.ll_field = 10;
MEM[(struct value *)arr_1(D) + 16B].type_code = 19;
MEM[(struct value *)arr_1(D) + 16B].union_field.i_field = 0;
MEM[(struct value *)arr_1(D) + 16B].type_code = 0;
return;
}
Note that the final:
MEM[(struct value *)arr_1(D) + 16B].union_field.i_field = 0;
is still present, and the lack of the:
> Deleted redundant store MEM[(struct value *)arr_2(D) +
> 16B].union_field.i_field = 0;
from the TDF_DETAILS version of the dump.
So for some reason fre1 is more aggressive on this with libgccjit than with
cc1.
