From 896048cf43d5eb21ab7c16553bb9d13b0f890b81 Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Thu, 3 Dec 2020 15:46:54 +0100 Subject: c++: Add __builtin_bit_cast to implement std::bit_cast [PR93121] The following patch adds __builtin_bit_cast builtin, similarly to clang or MSVC which implement std::bit_cast using such an builtin too. It checks the various std::bit_cast requirements, when not constexpr evaluated acts pretty much like VIEW_CONVERT_EXPR of the source argument to the destination type and the hardest part is obviously the constexpr evaluation. I've left out PDP11 handling of those, couldn't figure out how exactly are bitfields laid out there 2020-12-03 Jakub Jelinek PR libstdc++/93121 * fold-const.h (native_encode_initializer): Add mask argument defaulted to nullptr. (find_bitfield_repr_type): Declare. (native_interpret_aggregate): Declare. * fold-const.c (find_bitfield_repr_type): New function. (native_encode_initializer): Add mask argument and support for filling it. Handle also some bitfields without integral DECL_BIT_FIELD_REPRESENTATIVE. (native_interpret_aggregate): New function. * gimple-fold.h (clear_type_padding_in_mask): Declare. * gimple-fold.c (struct clear_padding_struct): Add clear_in_mask member. (clear_padding_flush): Handle buf->clear_in_mask. (clear_padding_union): Copy clear_in_mask. Don't error if buf->clear_in_mask is set. (clear_padding_type): Don't error if buf->clear_in_mask is set. (clear_type_padding_in_mask): New function. (gimple_fold_builtin_clear_padding): Set buf.clear_in_mask to false. * doc/extend.texi (__builtin_bit_cast): Document. * c-common.h (enum rid): Add RID_BUILTIN_BIT_CAST. * c-common.c (c_common_reswords): Add __builtin_bit_cast. * cp-tree.h (cp_build_bit_cast): Declare. * cp-tree.def (BIT_CAST_EXPR): New tree code. * cp-objcp-common.c (names_builtin_p): Handle RID_BUILTIN_BIT_CAST. (cp_common_init_ts): Handle BIT_CAST_EXPR. * cxx-pretty-print.c (cxx_pretty_printer::postfix_expression): Likewise. * parser.c (cp_parser_postfix_expression): Handle RID_BUILTIN_BIT_CAST. * semantics.c (cp_build_bit_cast): New function. * tree.c (cp_tree_equal): Handle BIT_CAST_EXPR. (cp_walk_subtrees): Likewise. * pt.c (tsubst_copy): Likewise. * constexpr.c (check_bit_cast_type, cxx_eval_bit_cast): New functions. (cxx_eval_constant_expression): Handle BIT_CAST_EXPR. (potential_constant_expression_1): Likewise. * cp-gimplify.c (cp_genericize_r): Likewise. * g++.dg/cpp2a/bit-cast1.C: New test. * g++.dg/cpp2a/bit-cast2.C: New test. * g++.dg/cpp2a/bit-cast3.C: New test. * g++.dg/cpp2a/bit-cast4.C: New test. * g++.dg/cpp2a/bit-cast5.C: New test. --- gcc/fold-const.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'gcc/fold-const.h') diff --git a/gcc/fold-const.h b/gcc/fold-const.h index e833019..818c3d5 100644 --- a/gcc/fold-const.h +++ b/gcc/fold-const.h @@ -27,9 +27,11 @@ extern int folding_initializer; /* Convert between trees and native memory representation. */ extern int native_encode_expr (const_tree, unsigned char *, int, int off = -1); extern int native_encode_initializer (tree, unsigned char *, int, - int off = -1); + int off = -1, unsigned char * = nullptr); extern tree native_interpret_expr (tree, const unsigned char *, int); extern bool can_native_interpret_type_p (tree); +extern tree native_interpret_aggregate (tree, const unsigned char *, int, int); +extern tree find_bitfield_repr_type (int, int); extern void shift_bytes_in_array_left (unsigned char *, unsigned int, unsigned int); extern void shift_bytes_in_array_right (unsigned char *, unsigned int, -- cgit v1.1