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builtins: Force SAVE_EXPR for __builtin_{add,sub,mul}_overflow and __builtin{add,sub}c [PR108789]

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The following testcase is miscompiled, because we use save_expr
on the .{ADD,SUB,MUL}_OVERFLOW call we are creating, but if the first
two operands are not INTEGER_CSTs (in that case we just fold it right away)
but are TREE_READONLY/!TREE_SIDE_EFFECTS, save_expr doesn't actually
create a SAVE_EXPR at all and so we lower it to
*arg2 = REALPART_EXPR (.ADD_OVERFLOW (arg0, arg1)), \
IMAGPART_EXPR (.ADD_OVERFLOW (arg0, arg1))
which evaluates the ifn twice and just hope it will be CSEd back.
As *arg2 aliases *arg0, that is not the case.
The builtins are really never const/pure as they store into what
the third arguments points to, so after handling the INTEGER_CST+INTEGER_CST
case, I think we should just always use SAVE_EXPR.  Just building SAVE_EXPR
by hand and setting TREE_SIDE_EFFECTS on it doesn't work, because
c_fully_fold optimizes it away again, so the following patch marks the
ifn calls as TREE_SIDE_EFFECTS (but doesn't do it for the
__builtin_{add,sub,mul}_overflow_p case which were designed for use
especially in constant expressions and don't really evaluate the
realpart side, so we don't really need a SAVE_EXPR in that case).

2024-06-04  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/108789
	* builtins.cc (fold_builtin_arith_overflow): For ovf_only,
	don't call save_expr and don't build REALPART_EXPR, otherwise
	set TREE_SIDE_EFFECTS on call before calling save_expr.
	(fold_builtin_addc_subc): Set TREE_SIDE_EFFECTS on call before
	calling save_expr.

	* gcc.c-torture/execute/pr108789.c: New test.

(cherry picked from commit b8e28381cb5c0cddfe5201faf799d8b27f5d7d6c)
This commit is contained in:
Jakub Jelinek 2024-06-04 12:28:01 +02:00
parent 1c1bc2553f
commit f9af4a05e0
2 changed files with 60 additions and 1 deletions
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22
gcc/builtins.cc
View file

@ -10042,7 +10042,21 @@ fold_builtin_arith_overflow (location_t loc, enum built_in_function fcode,
tree ctype = build_complex_type (type);
tree call = build_call_expr_internal_loc (loc, ifn, ctype, 2,
arg0, arg1);
tree tgt = save_expr (call);
tree tgt;
if (ovf_only)
{
tgt = call;
intres = NULL_TREE;
}
else
{
/* Force SAVE_EXPR even for calls which satisfy tree_invariant_p_1,
as while the call itself is const, the REALPART_EXPR store is
certainly not. And in any case, we want just one call,
not multiple and trying to CSE them later. */
TREE_SIDE_EFFECTS (call) = 1;
tgt = save_expr (call);
}
intres = build1_loc (loc, REALPART_EXPR, type, tgt);
ovfres = build1_loc (loc, IMAGPART_EXPR, type, tgt);
ovfres = fold_convert_loc (loc, boolean_type_node, ovfres);
@ -10354,11 +10368,17 @@ fold_builtin_addc_subc (location_t loc, enum built_in_function fcode,
tree ctype = build_complex_type (type);
tree call = build_call_expr_internal_loc (loc, ifn, ctype, 2,
args[0], args[1]);
/* Force SAVE_EXPR even for calls which satisfy tree_invariant_p_1,
as while the call itself is const, the REALPART_EXPR store is
certainly not. And in any case, we want just one call,
not multiple and trying to CSE them later. */
TREE_SIDE_EFFECTS (call) = 1;
tree tgt = save_expr (call);
tree intres = build1_loc (loc, REALPART_EXPR, type, tgt);
tree ovfres = build1_loc (loc, IMAGPART_EXPR, type, tgt);
call = build_call_expr_internal_loc (loc, ifn, ctype, 2,
intres, args[2]);
TREE_SIDE_EFFECTS (call) = 1;
tgt = save_expr (call);
intres = build1_loc (loc, REALPART_EXPR, type, tgt);
tree ovfres2 = build1_loc (loc, IMAGPART_EXPR, type, tgt);

39
gcc/testsuite/gcc.c-torture/execute/pr108789.c Normal file
View file

@ -0,0 +1,39 @@
/* PR middle-end/108789 */
int
add (unsigned *r, const unsigned *a, const unsigned *b)
{
return __builtin_add_overflow (*a, *b, r);
}
int
mul (unsigned *r, const unsigned *a, const unsigned *b)
{
return __builtin_mul_overflow (*a, *b, r);
}
int
main ()
{
unsigned x;
/* 1073741824U + 1073741824U should not overflow. */
x = (__INT_MAX__ + 1U) / 2;
if (add (&x, &x, &x))
__builtin_abort ();
/* 256U * 256U should not overflow */
x = 1U << (sizeof (int) * __CHAR_BIT__ / 4);
if (mul (&x, &x, &x))
__builtin_abort ();
/* 2147483648U + 2147483648U should overflow */
x = __INT_MAX__ + 1U;
if (!add (&x, &x, &x))
__builtin_abort ();
/* 65536U * 65536U should overflow */
x = 1U << (sizeof (int) * __CHAR_BIT__ / 2);
if (!mul (&x, &x, &x))
__builtin_abort ();
}