https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104280
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P1
Last reconfirmed| |2022-01-29
CC| |jakub at gcc dot gnu.org
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
To me this looks like a bug in gimple-fold.cc.
The r12-6924-gc2b610e7c6c89fd4 simplifies
_5 = 1 / c.0_4;
into
_5 = c.0_4 == 1;
As it is unsigned division, that is perfectly fine.
But then gimple-fold.cc's
/* Try to canonicalize for boolean-typed X the comparisons
X == 0, X == 1, X != 0, and X != 1. */
if (gimple_assign_rhs_code (stmt) == EQ_EXPR
|| gimple_assign_rhs_code (stmt) == NE_EXPR)
{
tree lhs = gimple_assign_lhs (stmt);
tree op1 = gimple_assign_rhs1 (stmt);
tree op2 = gimple_assign_rhs2 (stmt);
tree type = TREE_TYPE (op1);
/* Check whether the comparison operands are of the same boolean
type as the result type is.
Check that second operand is an integer-constant with value
one or zero. */
if (TREE_CODE (op2) == INTEGER_CST
&& (integer_zerop (op2) || integer_onep (op2))
&& useless_type_conversion_p (TREE_TYPE (lhs), type))
{
enum tree_code cmp_code = gimple_assign_rhs_code (stmt);
bool is_logical_not = false;
/* X == 0 and X != 1 is a logical-not.of X
X == 1 and X != 0 is X */
if ((cmp_code == EQ_EXPR && integer_zerop (op2))
|| (cmp_code == NE_EXPR && integer_onep (op2)))
is_logical_not = true;
if (is_logical_not == false)
gimple_assign_set_rhs_with_ops (gsi, TREE_CODE (op1), op1);
/* Only for one-bit precision typed X the transformation
!X -> ~X is valied. */
else if (TYPE_PRECISION (type) == 1)
gimple_assign_set_rhs_with_ops (gsi, BIT_NOT_EXPR, op1);
/* Otherwise we use !X -> X ^ 1. */
else
gimple_assign_set_rhs_with_ops (gsi, BIT_XOR_EXPR, op1,
build_int_cst (type, 1));
changed = true;
break;
}
}
kicks in and incorrectly "simplifies" it further into
_5 = c.0_4;
The comment talks about boolean type but nothing really checks that it is a
boolean or precision 1 type,
perhaps it expects that EQ_EXPR/NE_EXPR result must be boolean-ish, but that is
not true.
So, I think this optimization needs to be guarded on gimple_truth_valued_p
(op1, valueize)
but unfortunately while the function is not static inside of gimple-match.cc,
it isn't declared in any header.
