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c++: Drop alignas restriction for stack variables. 

Since expand_stack_vars and such know how to deal with variables aligned
beyond MAX_SUPPORTED_STACK_ALIGNMENT, we shouldn't reject alignas of large
alignments.  And if we don't do that, there's no point in having
check_cxx_fundamental_alignment_constraints at all, since
check_user_alignment already enforces MAX_OFILE_ALIGNMENT.

	PR c++/89357
	* c-attribs.c (check_cxx_fundamental_alignment_constraints): Remove.
This commit is contained in:
Jason Merrill 2020-01-29 17:16:12 -05:00
parent 8be8e32faf
commit e3b6c052b6
3 changed files with 20 additions and 61 deletions
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5
gcc/c-family/ChangeLog
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@ -1,3 +1,8 @@
2020-01-29 Jason Merrill <jason@redhat.com>
PR c++/89357
* c-attribs.c (check_cxx_fundamental_alignment_constraints): Remove.
2020-01-23 Jason Merrill <jason@redhat.com>
* c-warn.c (conversion_warning): Change -Wsign-conversion handling.

62
gcc/c-family/c-attribs.c
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@ -1957,65 +1957,6 @@ fail:
return res;
}
/* If in c++-11, check if the c++-11 alignment constraint with respect
to fundamental alignment (in [dcl.align]) are satisfied. If not in
c++-11 mode, does nothing.
[dcl.align]2/ says:
[* if the constant expression evaluates to a fundamental alignment,
the alignment requirement of the declared entity shall be the
specified fundamental alignment.
* if the constant expression evaluates to an extended alignment
and the implementation supports that alignment in the context
of the declaration, the alignment of the declared entity shall
be that alignment
* if the constant expression evaluates to an extended alignment
and the implementation does not support that alignment in the
context of the declaration, the program is ill-formed]. */
static bool
check_cxx_fundamental_alignment_constraints (tree node,
unsigned align_log,
int flags)
{
bool alignment_too_large_p = false;
unsigned requested_alignment = (1U << align_log) * BITS_PER_UNIT;
unsigned max_align = 0;
if ((!(flags & ATTR_FLAG_CXX11) && !warn_cxx_compat)
|| (node == NULL_TREE || node == error_mark_node))
return true;
if (cxx_fundamental_alignment_p (requested_alignment))
return true;
if (VAR_P (node))
{
if (TREE_STATIC (node) || DECL_EXTERNAL (node))
/* For file scope variables and static members, the target supports
alignments that are at most MAX_OFILE_ALIGNMENT. */
max_align = MAX_OFILE_ALIGNMENT;
else
/* For stack variables, the target supports at most
MAX_STACK_ALIGNMENT. */
max_align = MAX_STACK_ALIGNMENT;
if (requested_alignment > max_align)
alignment_too_large_p = true;
}
/* Let's be liberal for types and fields; don't limit their alignment any
more than check_user_alignment already did. */
if (alignment_too_large_p)
pedwarn (input_location, OPT_Wattributes,
"requested alignment %d is larger than %d",
requested_alignment / BITS_PER_UNIT, max_align / BITS_PER_UNIT);
return !alignment_too_large_p;
}
/* Common codes shared by handle_warn_if_not_aligned_attribute and
handle_aligned_attribute. */
@ -2059,8 +2000,7 @@ common_handle_aligned_attribute (tree *node, tree name, tree args, int flags,
/* Log2 of specified alignment. */
int pow2align = check_user_alignment (align_expr, objfile,
/* warn_zero = */ true);
if (pow2align == -1
|| !check_cxx_fundamental_alignment_constraints (*node, pow2align, flags))
if (pow2align == -1)
{
*no_add_attrs = true;
return NULL_TREE;

14
gcc/testsuite/g++.dg/cpp0x/alignas17.C Normal file
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@ -0,0 +1,14 @@
// PR c++/89357
// { dg-do compile { target c++11 } }
void g(int &);
void f0() {
__attribute__((aligned(128))) static int x;
g(x);
}
void f1() {
alignas(128) int x;
g(x);
}