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fold-const: Fix A <= 0 ? A : -A folding [PR95810]

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We folded A <= 0 ? A : -A into -ABS (A), which is for signed integral types
incorrect - can invoke on INT_MIN UB twice, once on ABS and once on its
negation.

The following patch fixes it by instead folding it to (type)-ABSU (A).

2020-06-24  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/95810
	* fold-const.c (fold_cond_expr_with_comparison): Optimize
	A <= 0 ? A : -A into (type)-absu(A) rather than -abs(A).

	* gcc.dg/ubsan/pr95810.c: New test.
This commit is contained in:
Jakub Jelinek 2020-06-24 10:40:02 +02:00
parent f0008858de
commit 01e10b0ee7
2 changed files with 29 additions and 2 deletions
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18
gcc/fold-const.c
View File

@ -5770,8 +5770,22 @@ fold_cond_expr_with_comparison (location_t loc, tree type,
case LT_EXPR:
if (TYPE_UNSIGNED (TREE_TYPE (arg1)))
break;
tem = fold_build1_loc (loc, ABS_EXPR, TREE_TYPE (arg1), arg1);
return negate_expr (fold_convert_loc (loc, type, tem));
if (ANY_INTEGRAL_TYPE_P (TREE_TYPE (arg1))
&& !TYPE_OVERFLOW_WRAPS (TREE_TYPE (arg1)))
{
/* A <= 0 ? A : -A for A INT_MIN is valid, but -abs(INT_MIN)
is not, invokes UB both in abs and in the negation of it.
So, use ABSU_EXPR instead. */
tree utype = unsigned_type_for (TREE_TYPE (arg1));
tem = fold_build1_loc (loc, ABSU_EXPR, utype, arg1);
tem = negate_expr (tem);
return fold_convert_loc (loc, type, tem);
}
else
{
tem = fold_build1_loc (loc, ABS_EXPR, TREE_TYPE (arg1), arg1);
return negate_expr (fold_convert_loc (loc, type, tem));
}
default:
gcc_assert (TREE_CODE_CLASS (comp_code) == tcc_comparison);
break;

13
gcc/testsuite/gcc.dg/ubsan/pr95810.c Normal file
View File

@ -0,0 +1,13 @@
/* PR middle-end/95810 */
/* { dg-do run } */
/* { dg-options "-fsanitize=undefined -fno-sanitize-recover=undefined" } */
int
main ()
{
int x = -__INT_MAX__ - 1;
x = (x <= 0 ? x : -x);
if (x != -__INT_MAX__ - 1)
__builtin_abort ();
return 0;
}