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Correct uninitialized object offset and size computation [PR101494].

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Resolves:
PR middle-end/101494 - -Wuninitialized false alarm with memrchr of size 0

gcc/ChangeLog:

	PR middle-end/101494
	* tree-ssa-uninit.c (maybe_warn_operand): Correct object offset
	and size computation.

gcc/testsuite/ChangeLog:

	PR middle-end/101494
	* gcc.dg/uninit-pr101494.c: New test.
This commit is contained in:
Martin Sebor 2021-07-28 16:25:40 -06:00
parent b9cbf8c9e0
commit 1121e495b7
2 changed files with 72 additions and 8 deletions
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60
gcc/testsuite/gcc.dg/uninit-pr101494.c Normal file
View file

@ -0,0 +1,60 @@
/* PR middle-end/101494 - bogus -Wmaybe-uninitialized on memrchr of size 0
{ dg-do compile }
{ dg-options "-O2 -Wall" } */
typedef __SIZE_TYPE__ size_t;
void* alloca (size_t);
__attribute__ ((malloc, alloc_size (1))) void* alloc (size_t);
__attribute__ ((access (read_only, 1, 2))) void* sink (void*, size_t);
void test_alloca_zero (size_t i)
{
char *p = alloca (0);
sink (p, 0); // { dg-bogus "\\\[-Wuninitialized" }
}
void test_alloca_zero_pi (size_t i)
{
char *p = alloca (0);
sink (p + i, 0);
}
void test_alloca_cst (void)
{
char *p = alloca (7);
sink (p, 0); // { dg-bogus "\\\[-Wuninitialized" }
}
void test_alloca_cst_p1 (void)
{
char *p = alloca (7);
sink (p + 1, 0); // { dg-bogus "\\\[-Wuninitialized" }
}
void test_alloca_cst_p7 (void)
{
char *p = alloca (7);
sink (p + 7, 0); // { dg-bogus "\\\[-Wuninitialized" }
}
void test_alloca_var (size_t n)
{
char *p = alloca (n);
sink (p, 0); // { dg-bogus "\\\[-Wuninitialized" }
}
void test_alloca_var_p1 (size_t n)
{
char *p = alloca (n);
sink (p + 1, 0); // { dg-bogus "\\\[-Wuninitialized" }
}
void test_alloca_var_pn (size_t n)
{
char *p = alloca (n);
sink (p + n, 0); // { dg-bogus "\\\[-Wuninitialized" }
}

20
gcc/tree-ssa-uninit.c
View file

@ -371,16 +371,20 @@ maybe_warn_operand (ao_ref &ref, gimple *stmt, tree lhs, tree rhs,
|| get_no_uninit_warning (base))
return NULL_TREE;
/* Do not warn if the access is fully outside of the variable. */
/* Do not warn if the access is zero size or if it's fully outside
the object. */
poly_int64 decl_size;
if (known_size_p (ref.size)
&& known_eq (ref.max_size, ref.size)
&& (known_eq (ref.size, 0)
|| known_le (ref.offset + ref.size, 0)))
return NULL_TREE;
if (DECL_P (base)
&& ((known_size_p (ref.size)
&& known_eq (ref.max_size, ref.size)
&& known_le (ref.offset + ref.size, 0))
|| (known_ge (ref.offset, 0)
&& DECL_SIZE (base)
&& poly_int_tree_p (DECL_SIZE (base), &decl_size)
&& known_le (decl_size, ref.offset))))
&& known_ge (ref.offset, 0)
&& DECL_SIZE (base)
&& poly_int_tree_p (DECL_SIZE (base), &decl_size)
&& known_le (decl_size, ref.offset))
return NULL_TREE;
/* Do not warn if the result of the access is then used for