https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121192
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
CC| |rguenth at gcc dot gnu.org
Last reconfirmed| |2025-07-21
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Hmm, so we turn this into
if (-(unsigned)({-1, -1}[0] == 0) != 0)
abort ()
so the change of ~ to - isn't correct (this is pr110817-1.c).
On GENERIC we have
V v = VEC_COND_EXPR < <<< Unknown tree: compound_literal_expr
V D.2272 = { 0, 0 }; >>> == { 0, 0 } , { 0, 0 } , { 4294967295,
4294967295 } > ;
so the bitwise not got elided already via
Applying pattern match.pd:5981, generic-match-3.cc:5023
before vector lowering it's correct:
<bb 2> :
_1 = { -1, -1 };
_2 = VEC_COND_EXPR <_1, { 0, 0 }, { 4294967295, 4294967295 }>;
v = _2;
_3 = BIT_FIELD_REF <v, 32, 0>;
if (_3 != 0)
goto <bb 3>; [INV]
else
goto <bb 4>; [INV]
<bb 3> :
__builtin_abort ();
but vector lowering makes a mess out of it. In particular we apply
Applying pattern match.pd:7027, gimple-match-6.cc:6659
Applying pattern match.pd:1685, gimple-match-1.cc:10846
Applying pattern match.pd:6272, gimple-match-1.cc:24830
(simplify
(cond @0 INTEGER_CST@1 INTEGER_CST@2)
(switch
...
(if (integer_zerop (@1))
(switch
/* a ? 0 : 1 -> !a. */
(if (integer_onep (@2))
(convert (bit_xor (convert:boolean_type_node @0) { boolean_true_node; })))
/* a ? 0 : -1 -> -(!a). */
(if (INTEGRAL_TYPE_P (type) && integer_all_onesp (@2))
(if (TYPE_PRECISION (type) == 1)
/* For signed 1-bit precision just cast bool to the type. */
(convert (bit_xor (convert:boolean_type_node @0) { boolean_true_node; }))
(if (TREE_CODE (type) == BOOLEAN_TYPE)
(with {
tree intt = build_nonstandard_integer_type (TYPE_PRECISION (type),
TYPE_UNSIGNED (type));
}
(convert (negate (convert:intt (bit_xor (convert:boolean_type_node @0)
{ boolean_true_node; })))))
(negate (convert:type (bit_xor (convert:boolean_type_node @0)
{ boolean_true_node; }))))))
but this seems to confuse us. We try to generate
-(signed-boolean:32)((bool)({-1,-1}[0] != 0) ^ (bool)1)
and things go downhill from there with the X ^ ~0 -> ~X and
~(x != 0) -> x == 0 patterns.
One needs to see what vector lowering produces initially to decide whether
the issue is there or in the patterns above.
