https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105629
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
Status|UNCONFIRMED |ASSIGNED
Priority|P3 |P1
Last reconfirmed| |2022-05-23
Target| |x86_64-*-*
Ever confirmed|0 |1
Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot
gnu.org
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Thanks, so the relevant IL change is probably
# c$_M_value_3 = PHI <-1(3), 0(2), 2(5), 1(4)>
_11 = (unsigned char) c$_M_value_3;
_16 = _11 <= 1;
vs
# c$_M_value_3 = PHI <-1(3), 0(2), 2(5), 1(4)>
_11 = (unsigned int) c$_M_value_3;
_16 = _11 <= 1;
where the conversion from c$_M_value_3 is now sign-extending which is something
spaceship_replacement does not expect. We how do
Matching expression match.pd:2114, generic-match.cc:676
Matching expression match.pd:2121, generic-match.cc:736
Applying pattern match.pd:5497, generic-match.cc:23783 (****)
Matching expression match.pd:2114, generic-match.cc:676
Matching expression match.pd:2121, generic-match.cc:736
Matching expression match.pd:2126, generic-match.cc:776
Applying pattern match.pd:5868, generic-match.cc:62355
Applying pattern match.pd:3662, generic-match.cc:27474
Applying pattern match.pd:3742, generic-match.cc:26853
Applying pattern match.pd:3648, generic-match.cc:27432
;; Function constexpr bool std::operator>=(partial_ordering,
__cmp_cat::__unspec) (null)
;; enabled by -tree-original
<<< Unknown tree: must_not_throw_expr
return <retval> = (unsigned int) __v._M_value <= 1
>>>;
with the marked (****) folding that eventually you re-disable for GENERIC.
In the end we use .SPACESHIP on x86_64 but end up with
bool f17 (double i)
{
bool _2;
int _7;
bool prephitmp_8;
<bb 2> [local count: 1073741824]:
_7 = .SPACESHIP (i_1(D), 5.0e+0);
if (_7 != 0)
goto <bb 3>; [50.00%]
else
goto <bb 5>; [50.00%]
<bb 3> [local count: 536870913]:
if (_7 == 1)
goto <bb 4>; [50.00%]
else
goto <bb 5>; [50.00%]
<bb 4> [local count: 268435456]:
_2 = i_1(D) > 5.0e+0;
<bb 5> [local count: 1073741824]:
# prephitmp_8 = PHI <1(2), _2(4), 0(3)>
return prephitmp_8;
which is a regression from GCC 12. I think the non-widening constraint can
be relaxed. Indeed the following fixes it - Jakub, is there anything
that would prevent sign-extending to work?
diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index 8c9c46d41f1..e61d9736937 100644
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -2217,7 +2217,7 @@ spaceship_replacement (basic_block cond_bb, basic_block
middle_bb,
if (!TYPE_UNSIGNED (ty2) || !INTEGRAL_TYPE_P (ty2))
return false;
- if (TYPE_PRECISION (ty1) != TYPE_PRECISION (ty2))
+ if (TYPE_PRECISION (ty1) > TYPE_PRECISION (ty2))
return false;
if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (orig_use_lhs))
return false;
