https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109596
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Loooking at pr90716.c, that case seems like a clear wrong-debug.
Before r14-162 j was <optimized out> everywhere, "j\0" DW_TAG_variable didn't
have any DW_AT_location/DW_AT_const_value, optimized dump doesn't show any
DEBUG stmts for j nor any references to it, etc.
With r14-162 and later the DW_TAG_variable has DW_AT_const_value 0, which is
wrong,
if anything it should have DW_AT_const_value 8.
Optimized dump difference is
--- pr90716.c.254t.optimized_ 2024-03-19 10:23:03.688427714 -0400
+++ pr90716.c.254t.optimized 2024-03-19 10:23:39.351797960 -0400
@@ -18,19 +18,20 @@ void optimize_me_not ()
int main ()
{
<bb 2> [local count: 17041817]:
# DEBUG BEGIN_STMT
# DEBUG BEGIN_STMT
# DEBUG b => 0
# DEBUG BEGIN_STMT
# DEBUG b => 0
# DEBUG BEGIN_STMT
__builtin_memset (&a, 0, 224);
- # DEBUG b => NULL
+ # DEBUG j => 0
+ # DEBUG b => 0
# DEBUG BEGIN_STMT
optimize_me_not ();
# DEBUG BEGIN_STMT
return 0;
}
Clearly even the b value is wrong, that again should be either 8 or NULL after
the loops.
Before ch2 pass, the IL is the same with r14-161 and r14-162:
<bb 2> [local count: 17041817]:
# DEBUG b => 0
goto <bb 6>; [100.00%]
<bb 3> [local count: 954449105]:
a[b_1][j_2] = 0;
j_9 = j_2 + 1;
# DEBUG j => j_9
<bb 4> [local count: 1073741824]:
# j_2 = PHI <0(8), j_9(3)>
# DEBUG j => j_2
if (j_2 != 8)
goto <bb 3>; [88.89%]
else
goto <bb 5>; [11.11%]
<bb 5> [local count: 119292720]:
b_7 = b_1 + 1;
# DEBUG b => b_7
<bb 6> [local count: 136334537]:
# b_1 = PHI <0(2), b_7(5)>
# DEBUG b => b_1
if (b_1 != 7)
goto <bb 8>; [87.50%]
else
goto <bb 7>; [12.50%]
<bb 8> [local count: 119292720]:
goto <bb 4>; [100.00%]
<bb 7> [local count: 17041817]:
optimize_me_not ();
return 0;
but ch2 changes the IL (r14-161 vs. r14-162):
--- pr90716.c.126t.ch2_ 2024-03-19 11:20:14.311013575 -0400
+++ pr90716.c.126t.ch2 2024-03-19 11:20:18.879061929 -0400
@@ -72,44 +72,44 @@ Removing basic block 12
int main ()
{
int j;
int b;
<bb 2> [local count: 17041817]:
# DEBUG b => 0
# DEBUG b => 0
goto <bb 5>; [100.00%]
<bb 3> [local count: 954449105]:
# j_15 = PHI <j_9(3), 0(5)>
- # DEBUG j => j_15
a[b_14][j_15] = 0;
j_9 = j_15 + 1;
# DEBUG j => j_9
# DEBUG j => j_9
if (j_9 != 8)
goto <bb 3>; [88.89%]
else
goto <bb 4>; [11.11%]
<bb 4> [local count: 119292720]:
+ # DEBUG j => 0
b_7 = b_14 + 1;
# DEBUG b => b_7
# DEBUG b => b_7
if (b_7 != 7)
goto <bb 5>; [87.50%]
else
goto <bb 6>; [12.50%]
<bb 5> [local count: 119292720]:
# b_14 = PHI <b_7(4), 0(2)>
- # DEBUG b => b_14
# DEBUG j => 0
goto <bb 3>; [100.00%]
<bb 6> [local count: 17041817]:
+ # DEBUG b => 0
optimize_me_not ();
return 0;
}
The changes in r14-162 feel highly undesirable for debug info.
