expression: examine constness of conditionals at evaluation only
RFC PATCH 5/13 expression: examine constness of conditionals at evaluation only
Currently, the propagation of expressions' constness flags through conditional expressions is done in two steps:
- Several flags are speculatively set at expression parsing time
- and possibly cleared again at evaluation time.
Set aside this unfortunate split of code, the early propagation of constness flags is not able to recognize constant expressions such as
0 ? __builtin_choose_expr(0, 0, 0) : 0
0 ? 0 : __builtin_choose_expr(0, 0, 0)
since the final expression to be thrown into the conditional expression is known only after evaluation.
Move the whole calculation of conditional expressions' constness flags to the evaluation phase.
Introduce support for tracking arithmetic constness propagation through conditional expressions.
--- evaluate.c | 15 ++++++++------- expression.c | 7 ------- validation/constexpr-conditional.c | 34 ++++++++++++++++++++++++++++++++++ 3 files changed, 42 insertions(+), 14 deletions(-) create mode 100644 validation/constexpr-conditional.c
evaluate.c +8 -7
@@ -1113,13 +1113,14 @@ static struct symbol *evaluate_conditional_expression(struct expression *expr) true = &expr->cond_true; } -if (expr->flags) { -int flags = (expr->conditional->flags & -expr_set_flag_mask (EXPR_FLAG_INT_CONST_EXPR )); - flags &= (*true)->flags & expr->cond_false->flags; -if (!flags) - expr->flags =EXPR_FLAG_NONE ; - } + expr->flags |=expr_flags_decay_consts (expr->conditional->flags & + (*true)->flags & + expr->cond_false->flags); +/* +* A conditional operator never yields an address constant +* [6.6(9)]. +*/ + expr->flags &= ~expr_clear_flag_mask (EXPR_FLAG_ADDR_CONST_EXPR ); lclass =classify_type (ltype, <ype); rclass =classify_type (rtype, &rtype);
expression.c +0 -7
@@ -858,13 +858,6 @@ struct token *conditional_expression(struct token *token, struct expression **tr token =parse_expression (token->next, &expr->cond_true); token =expect (token,':' ,"in conditional expression" ); token =conditional_expression (token, &expr->cond_false); -if (expr->left && expr->cond_false) { -enum expression_flags flags = expr->left->flags & - expr->cond_false->flags; -if (expr->cond_true) - flags &= expr->cond_true->flags; - expr->flags =expr_flags_decay_consts (flags); - } }return token; }
validation/constexpr-conditional.c new file +34 -0
@@ -0,0 +1,34 @@ +static int a[] = { + [0 ? :0 ] =0 ,// OK + [1 ? :0 ] =0 ,// OK + [0 ?0 :0 ] =0 ,// OK + [1 ?0 :0 ] =0 ,// OK + [0 ?0 :__builtin_choose_expr (0 ,0 ,0 )] =0 ,// OK + [1 ?__builtin_choose_expr (0 ,0 ,0 ) :0 ] =0 ,// OK + [0 ?__builtin_choose_expr (0 ,0 ,0 ) :0 ] =0 ,// OK + [1 ?1 :__builtin_choose_expr (0 ,0 ,0 )] =0 ,// OK + [__builtin_choose_expr (0 ,0 ,0 ) ? :0 ] =0 ,// OK + [__builtin_choose_expr (0 ,0 ,1 ) ? :0 ] =0 ,// OK + [0. ? :0 ] =0 ,// KO + [0 ?0. :0 ] =0 ,// KO + [1 ? :0. ] =0 ,// KO + [__builtin_choose_expr (0 ,0. ,0 ) ? :0 ] =0 ,// OK + [__builtin_choose_expr (0 ,0 ,0. ) ? :0 ] =0 ,// KO + [0 ?__builtin_choose_expr (0 ,0. ,0 ) :0 ] =0 ,// OK + [0 ?__builtin_choose_expr (0 ,0 ,0. ) :0 ] =0 ,// KO + [1 ?0 :__builtin_choose_expr (0 ,0. ,0 )] =0 ,// OK + [1 ?0 :__builtin_choose_expr (0 ,0 ,0. )] =0 ,// KO +}; + +/* +* check-name: Expression constness propagation in conditional expressions +* +* check-error-start +constexpr-conditional.c:12:13: error: bad constant expression +constexpr-conditional.c:13:19: error: bad constant expression +constexpr-conditional.c:14:12: error: bad constant expression +constexpr-conditional.c:16:42: error: bad constant expression +constexpr-conditional.c:18:48: error: bad constant expression +constexpr-conditional.c:20:14: error: bad constant expression +* check-error-end +*/
Signature · 1 line
2.4.5