https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106114
Aldy Hernandez <aldyh at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P1
CC| |law at gcc dot gnu.org
--- Comment #5 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
I think this is fold_using_range getting confused with DOM changing the IL from
under it.
fold_using_range::relation_fold_and_or() is (incorrectly) folding the final
conditional as always true:
<bb 2> [local count: 79134772]:
a.0_1 = a;
b = a.0_1;
a.1_15 = a.0_1;
_16 = a.0_1 < -117;
_17 = a.0_1 >= -83;
_18 = _16 | _17;
if (_18 != 0)
But the IL on entry to DOM is actually:
<bb 2> [local count: 79134772]:
a.0_1 = a;
b = a.0_1;
a.1_15 = a;
_16 = a.1_15 < -117;
_17 = a.1_15 >= -83;
_18 = _16 | _17;
if (_18 != 0)
DOM replaced a.1_15=a with a.1_15=a.0_1:
Optimizing statement a.1_15 = a;
LKUP STMT a.1_15 = a with .MEM_7
FIND: a.0_1
Replaced redundant expr 'a' with 'a.0_1'
...and then cproped the a.1_15 into the uses:
Optimizing statement _16 = a.1_15 < -117;
Replaced 'a.1_15' with variable 'a.0_1'
Optimizing statement _17 = a.1_15 >= -83;
Replaced 'a.1_15' with variable 'a.0_1'
By the time we get to the conditional, the ranger thinks it can fold the
conditional:
Optimizing statement if (_18 != 0)
Relation adjustment: _16 and _17 combine to produce [irange] _Bool [1, 1]
Replaced '_18' with constant '1'
Since the IL on entry to DOM is different than what evrp would see, I added an
evrp instance before DOM and ran it with -O2 -fno-tree-dominator-opts, but evrp
does not fold the conditional. So this is something particular to what we're
doing in DOM.
In this hacked up evrp instance I see ssa1_dep2 and ssa2_dep2 are both NULL
when we query "_18 = _16 | _17", so we never fold the conditional:
// Both names will need to have 2 direct dependencies.
tree ssa1_dep2 = src.gori ()->depend2 (ssa1);
tree ssa2_dep2 = src.gori ()->depend2 (ssa2);
if (!ssa1_dep2 || !ssa2_dep2)
return;
(gdb) p ssa1_dep2
$35 = <tree 0x0>
(gdb) p ssa2_dep2
$36 = <tree 0x0>
OTOH, in DOM we have:
(gdb) p debug(ssa1_dep2)
a.0_1
$33 = void
(gdb) p debug(ssa2_dep2)
a.0_1
$34 = void
(gdb)
So the dependencies in DOM's use of ranger in flight are different than what
evrp would see.
Andrew, would the changed IL cause the folding problem above?
