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author | Jakub Jelinek <jakub@redhat.com> | 2020-04-29 09:01:49 +0200 |
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committer | Jakub Jelinek <jakub@redhat.com> | 2020-04-29 09:01:49 +0200 |
commit | 575ac27fd5f18ffc9cfce8a99e987f52c5b898c9 (patch) | |
tree | b5a4515fb2bf50360866c27ed81640a59822904c /gcc/calls.c | |
parent | df30ab70690d6088f367e74757f0b5dd6a2587e5 (diff) | |
download | gcc-575ac27fd5f18ffc9cfce8a99e987f52c5b898c9.zip gcc-575ac27fd5f18ffc9cfce8a99e987f52c5b898c9.tar.gz gcc-575ac27fd5f18ffc9cfce8a99e987f52c5b898c9.tar.bz2 |
c++, middle-end, rs6000: Fix C++17 ABI incompatibilities during class layout and [[no_unique_address]] handling [PR94707]
As reported by Iain and David, powerpc-darwin and powerpc-aix* have C++14
vs. C++17 ABI incompatibilities which are not fixed by mere adding of
cxx17_empty_base_field_p calls. Unlike the issues that were seen on other
targets where the artificial empty base field affected function argument
passing or returning of values, on these two targets the difference is
during class layout, not afterwards (e.g.
struct empty_base {};
struct S : public empty_base { unsigned long long l[2]; };
will have different __alignof__ (S) between C++14 and C++17 (or possibly
with double instead of unsigned long long too)).
I've tried:
struct X { };
struct Y { int : 0; };
struct Z { int : 0; Y y; };
struct U : public X { X q; };
struct A { float a, b, c, d; };
struct B : public X { float a, b, c, d; };
struct C : public Y { float a, b, c, d; };
struct D : public Z { float a, b, c, d; };
struct E : public U { float a, b, c, d; };
struct F { [[no_unique_address]] X x; float a, b, c, d; };
struct G { [[no_unique_address]] Y y; float a, b, c, d; };
struct H { [[no_unique_address]] Z z; float a, b, c, d; };
struct I { [[no_unique_address]] U u; float a, b, c, d; };
struct J { float a, b; [[no_unique_address]] X x; float c, d; };
struct K { float a, b; [[no_unique_address]] Y y; float c, d; };
struct L { float a, b; [[no_unique_address]] Z z; float c, d; };
struct M { float a, b; [[no_unique_address]] U u; float c, d; };
#define T(S, s) extern S s; extern void foo##s (S); int bar##s () { foo##s (s); return 0; }
T (A, a)
T (B, b)
T (C, c)
T (D, d)
T (E, e)
T (F, f)
T (G, g)
T (H, h)
T (I, i)
T (J, j)
T (K, k)
T (L, l)
T (M, m)
testcase on powerpc64-linux. Results:
G++ 9 -std=c++14 A, B, C passed in fprs, the rest in gprs
G++ 9 -std=c++17 A passed in fprs, the rest in gprs
current trunk -std=c++14 & 17 A, B, C passed in fprs, the rest in gprs
patched trunk -std=c++14 & 17 A, B, C, F, G, J, K passed in fprs, the rest in gprs
clang++ [*] -std=c++14 & 17 A, B, C, F, G, J, K passed in fprs, the rest in gprs
[*] clang version 11.0.0 (git@github.com:llvm/llvm-project.git 5c352e69e76a26e4eda075e20aa6a9bb7686042c)
Is that what we want? I think it matches the stated intent of P0840R2 or
what Jason/Jonathan said, and doing something different like e.g. not
treating C, G and K as homogenous because of the int : 0 in empty bases
or in zero sized [[no_unique_address] fields would be quite hard to
implement (because for C++14 the FIELD_DECL just isn't there).
2020-04-29 Jakub Jelinek <jakub@redhat.com>
PR target/94707
* tree-core.h (tree_decl_common): Note decl_flag_0 used for
DECL_FIELD_ABI_IGNORED.
* tree.h (DECL_FIELD_ABI_IGNORED): Define.
* calls.h (cxx17_empty_base_field_p): Change into a temporary
macro, check DECL_FIELD_ABI_IGNORED flag with no "no_unique_address"
attribute.
* calls.c (cxx17_empty_base_field_p): Remove.
* tree-streamer-out.c (pack_ts_decl_common_value_fields): Handle
DECL_FIELD_ABI_IGNORED.
* tree-streamer-in.c (unpack_ts_decl_common_value_fields): Likewise.
* lto-streamer-out.c (hash_tree): Likewise.
* config/rs6000/rs6000-call.c (rs6000_aggregate_candidate): Rename
cxx17_empty_base_seen to empty_base_seen, change type to int *,
adjust recursive calls, use DECL_FIELD_ABI_IGNORED instead of
cxx17_empty_base_field_p, if "no_unique_address" attribute is
present, propagate that to the caller too.
(rs6000_discover_homogeneous_aggregate): Adjust
rs6000_aggregate_candidate caller, emit different diagnostics
when c++17 empty base fields are present and when empty
[[no_unique_address]] fields are present.
* config/rs6000/rs6000.c (rs6000_special_round_type_align,
darwin_rs6000_special_round_type_align): Skip DECL_FIELD_ABI_IGNORED
fields.
* class.c (build_base_field): Set DECL_FIELD_ABI_IGNORED on C++17 empty
base artificial FIELD_DECLs.
(layout_class_type): Set DECL_FIELD_ABI_IGNORED on empty class
field_poverlapping_p FIELD_DECLs.
* lto-common.c (compare_tree_sccs_1): Handle DECL_FIELD_ABI_IGNORED.
* g++.target/powerpc/pr94707-1.C: New test.
* g++.target/powerpc/pr94707-2.C: New test.
* g++.target/powerpc/pr94707-3.C: New test.
* g++.target/powerpc/pr94707-4.C: New test.
* g++.target/powerpc/pr94707-5.C: New test.
* g++.target/powerpc/pr94707-4.C: New test.
Diffstat (limited to 'gcc/calls.c')
-rw-r--r-- | gcc/calls.c | 18 |
1 files changed, 0 insertions, 18 deletions
diff --git a/gcc/calls.c b/gcc/calls.c index 9ac7f94..5bd9227 100644 --- a/gcc/calls.c +++ b/gcc/calls.c @@ -6261,23 +6261,5 @@ must_pass_va_arg_in_stack (tree type) return targetm.calls.must_pass_in_stack (arg); } -/* Return true if FIELD is the C++17 empty base field that should - be ignored for ABI calling convention decisions in order to - maintain ABI compatibility between C++14 and earlier, which doesn't - add this FIELD to classes with empty bases, and C++17 and later - which does. */ - -bool -cxx17_empty_base_field_p (const_tree field) -{ - return (TREE_CODE (field) == FIELD_DECL - && DECL_ARTIFICIAL (field) - && RECORD_OR_UNION_TYPE_P (TREE_TYPE (field)) - && DECL_SIZE (field) - && integer_zerop (DECL_SIZE (field)) - && TYPE_SIZE (TREE_TYPE (field)) - && !integer_zerop (TYPE_SIZE (TREE_TYPE (field)))); -} - /* Tell the garbage collector about GTY markers in this source file. */ #include "gt-calls.h" |