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mips: Fix C++14 vs. C++17 ABI incompatibility on mips64 

This fixes tmpdir-g++.dg-struct-layout-1/{t032,t059} failure.  Clang++
also ignores C++17 empty bases in return values.

gcc/
	* config/mips/mips.cc (mips_fpr_return_fields): Ignore
	cxx17_empty_base_field_p fields and set an indicator.
	(mips_return_in_msb): Adjust for mips_fpr_return_fields change.
	(mips_function_value_1): Inform psABI change about C++17 empty
	bases.

gcc/testsuite/
	* g++.target/mips/cxx17_empty_base.C: New test.
This commit is contained in:
Xi Ruoyao 2022-04-06 20:18:37 +08:00
parent 5df29fe79d
commit eac5c12c18
No known key found for this signature in database
GPG Key ID: D95E4716CCBB34DC
2 changed files with 73 additions and 5 deletions
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58
gcc/config/mips/mips.cc
View File

@ -6318,12 +6318,21 @@ mips_callee_copies (cumulative_args_t, const function_arg_info &arg)
The C++ FE used to remove zero-width bit-fields in GCC 11 and earlier.
To make a proper diagnostic, this function will set
HAS_CXX_ZERO_WIDTH_BF to true once a C++ zero-width bit-field shows up,
and then ignore it. Then the caller can determine if this zero-width
bit-field will make a difference and emit a -Wpsabi inform. */
and then ignore it.
We had failed to ignore C++17 empty bases in GCC 7, 8, 9, 10, and 11.
This caused an ABI incompatibility between C++14 and C++17. This is
fixed now and to make a proper diagnostic, this function will set
HAS_CXX17_EMPTY_BASE to true once a C++17 empty base shows up, and
then ignore it.
The caller should use the value of HAS_CXX17_EMPTY_BASE and/or
HAS_CXX_ZERO_WIDTH_BF to emit a proper -Wpsabi inform. */
static int
mips_fpr_return_fields (const_tree valtype, tree *fields,
bool *has_cxx_zero_width_bf)
bool *has_cxx_zero_width_bf,
bool *has_cxx17_empty_base)
{
tree field;
int i;
@ -6340,6 +6349,12 @@ mips_fpr_return_fields (const_tree valtype, tree *fields,
if (TREE_CODE (field) != FIELD_DECL)
continue;
if (cxx17_empty_base_field_p (field))
{
*has_cxx17_empty_base = true;
continue;
}
if (DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD (field))
{
*has_cxx_zero_width_bf = true;
@ -6375,8 +6390,13 @@ mips_return_in_msb (const_tree valtype)
tree fields[2];
bool has_cxx_zero_width_bf = false;
/* Its value is not used. */
bool has_cxx17_empty_base = false;
return (mips_fpr_return_fields (valtype, fields,
&has_cxx_zero_width_bf) == 0
&has_cxx_zero_width_bf,
&has_cxx17_empty_base) == 0
|| has_cxx_zero_width_bf);
}
@ -6473,11 +6493,18 @@ mips_function_value_1 (const_tree valtype, const_tree fn_decl_or_type,
mode = promote_function_mode (valtype, mode, &unsigned_p, func, 1);
bool has_cxx_zero_width_bf = false;
bool has_cxx17_empty_base = false;
int use_fpr = mips_fpr_return_fields (valtype, fields,
&has_cxx_zero_width_bf);
&has_cxx_zero_width_bf,
&has_cxx17_empty_base);
/* If has_cxx_zero_width_bf and has_cxx17_empty_base are both
true, it *happens* that there is no ABI change. So we won't
inform in this case. */
if (TARGET_HARD_FLOAT
&& warn_psabi
&& has_cxx_zero_width_bf
&& !has_cxx17_empty_base
&& use_fpr != 0)
{
static unsigned last_reported_type_uid;
@ -6499,6 +6526,27 @@ mips_function_value_1 (const_tree valtype, const_tree fn_decl_or_type,
if (has_cxx_zero_width_bf)
use_fpr = 0;
if (TARGET_HARD_FLOAT
&& warn_psabi
&& use_fpr != 0
&& has_cxx17_empty_base)
{
static unsigned last_reported_type_uid;
unsigned uid = TYPE_UID (TYPE_MAIN_VARIANT (valtype));
if (uid != last_reported_type_uid)
{
static const char *url
= CHANGES_ROOT_URL
"gcc-12/changes.html#mips_cxx17_empty_bases";
inform (input_location,
"the ABI for returning a value with C++17 empty "
"bases but otherwise an aggregate with only one or "
"two floating-point fields was changed in GCC "
"%{12.1%}", url);
last_reported_type_uid = uid;
}
}
/* Handle structures whose fields are returned in $f0/$f2. */
switch (use_fpr)
{

20
gcc/testsuite/g++.target/mips/cxx17_empty_base.C Normal file
View File

@ -0,0 +1,20 @@
// { dg-do compile }
// { dg-options "-O2 -std=c++17 -mabi=64 -mhard-float" }
// { dg-final { scan-assembler "\\\$f0" } }
struct empty {};
struct foo : empty
{
double a;
double b;
};
struct foo
make_foo(void) // { dg-message "the ABI for returning a value with C\\\+\\\+17 empty bases but otherwise an aggregate with only one or two floating-point fields was changed in GCC 12.1" }
{
struct foo ret;
ret.a = 114;
ret.b = 514;
return ret;
}