https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81227
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
As input we get:
(gdb) p debug_tree (val1)
<plus_expr 0x7ffff6d884b0
type <integer_type 0x7ffff6d572a0 public QI
size <integer_cst 0x7ffff6c3fdc8 constant 8>
unit size <integer_cst 0x7ffff6c3fde0 constant 1>
align 8 symtab 0 alias set -1 canonical type 0x7ffff6d572a0 precision 1
min <integer_cst 0x7ffff6d6a270 -1> max <integer_cst 0x7ffff6d6a288 0>>
arg 0 <ssa_name 0x7ffff6c4ac18 type <integer_type 0x7ffff6d572a0>
visited
def_stmt _9 = b.a;
version 9>
arg 1 <integer_cst 0x7ffff6d6a738 type <integer_type 0x7ffff6d572a0>
constant public overflow -1>>
that's from trying to set a symbolic range where we try to build
if (TYPE_PRECISION (TREE_TYPE (min)) == 1
&& !TYPE_UNSIGNED (TREE_TYPE (min)))
min = fold_build2 (MINUS_EXPR, TREE_TYPE (min), min,
build_int_cst (TREE_TYPE (min), -1));
thus _9 - -1 but that's folded to _9 + -1(OVF) via
/* A - B -> A + (-B) if B is easily negatable. */
(simplify
(minus @0 negate_expr_p@1)
(if (!FIXED_POINT_TYPE_P (type))
(plus @0 (negate @1))))
and
(match negate_expr_p
INTEGER_CST
(if ((INTEGRAL_TYPE_P (type)
&& TYPE_OVERFLOW_WRAPS (type))
|| (!TYPE_OVERFLOW_SANITIZED (type)
&& may_negate_without_overflow_p (t)))))
uncovering the old issue that implementation defined "overflow" still causes
TREE_OVERFLOW to be set. I suppose the above (copied from fold-const.c
negate_expr_p) should eventually not say that MSB only unsigned is easily
negated.
Or fold_negate_const should not do
case INTEGER_CST:
{
bool overflow;
wide_int val = wi::neg (arg0, &overflow);
t = force_fit_type (type, val, 1,
(overflow | TREE_OVERFLOW (arg0))
&& !TYPE_UNSIGNED (type));
but check && ! TYPE_OVERFLOW_WRAPS (type) here. OTOH int_const_binop
looks at the sign of the type only as well.
IMHO simplifying and aligning fold-const.c and match.pd here w/o changing
when we set TREE_OVERFLOW makes sense:
Index: gcc/fold-const.c
===================================================================
--- gcc/fold-const.c (revision 249435)
+++ gcc/fold-const.c (working copy)
@@ -383,9 +383,6 @@ negate_expr_p (tree t)
switch (TREE_CODE (t))
{
case INTEGER_CST:
- if (INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_WRAPS (type))
- return true;
-
/* Check that -CST will not overflow type. */
return may_negate_without_overflow_p (t);
case BIT_NOT_EXPR:
Index: gcc/match.pd
===================================================================
--- gcc/match.pd (revision 249435)
+++ gcc/match.pd (working copy)
@@ -834,10 +834,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
/* A few cases of fold-const.c negate_expr_p predicate. */
(match negate_expr_p
INTEGER_CST
- (if ((INTEGRAL_TYPE_P (type)
- && TYPE_OVERFLOW_WRAPS (type))
- || (!TYPE_OVERFLOW_SANITIZED (type)
- && may_negate_without_overflow_p (t)))))
+ (if (may_negate_without_overflow_p (t))))
(match negate_expr_p
FIXED_CST)
(match negate_expr_p
