expression: examine constness of preops at evaluation only
RFC PATCH 4/13 expression: examine constness of preops at evaluation only
Currently, the propagation of expressions' constness flags through prefix 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
-__builtin_choose_expr(0, 0, 0) ~__builtin_choose_expr(0, 0, 0) !__builtin_choose_expr(0, 0, 0)
since the final expression to be thrown into the prefix expression is known only after evaluation.
Move the whole calculation of prefix expressions' constness flags to the evaluation phase.
Introduce support for tracking arithmetic constness propagation through prefix expressions.
--- evaluate.c | 15 ++++++++++----- expression.c | 3 --- validation/constexpr-preop.c | 29 +++++++++++++++++++++++++++++ 3 files changed, 39 insertions(+), 8 deletions(-) create mode 100644 validation/constexpr-preop.c
evaluate.c +10 -5
@@ -1794,8 +1794,9 @@ static struct symbol *evaluate_sign(struct expression *expr) {struct symbol *ctype = expr->unop->ctype;int class =classify_type (ctype, &ctype); -if (expr->flags && !(expr->unop->flags &EXPR_FLAG_INT_CONST_EXPR )) - expr->flags =EXPR_FLAG_NONE ; +enum expression_flags flags; + + flags = expr->flags |expr_flags_decay_consts (expr->unop->flags);/* should be an arithmetic type */ if (!(class &TYPE_NUM ))return bad_expr_type (expr);
@@ -1812,6 +1813,7 @@ Normal: }if (expr->op =='+' ) *expr = *expr->unop; + expr->flags = flags; expr->ctype = ctype;return ctype; Restr:
@@ -1849,9 +1851,12 @@ static struct symbol *evaluate_preop(struct expression *expr)return evaluate_postop (expr);case '!' : -if (expr->flags && !(expr->unop->flags & -EXPR_FLAG_INT_CONST_EXPR )) - expr->flags =EXPR_FLAG_NONE ; + expr->flags |=expr_flags_decay_consts (expr->unop->flags); +/* +* A logical negation never yields an address constant +* [6.6(9)]. +*/ + expr->flags &= ~expr_clear_flag_mask (EXPR_FLAG_ADDR_CONST_EXPR );if (is_safe_type (ctype))warning (expr->pos,"testing a 'safe expression'" );if (is_float_type (ctype)) {
expression.c +0 -3
@@ -451,8 +451,6 @@ struct token *primary_expression(struct token *token, struct expression **tree) expr =alloc_expression (token->pos,EXPR_PREOP ); expr->op ='(' ; token =parens_expression (token, &expr->unop,"in expression" ); -if (expr->unop) - expr->flags = expr->unop->flags;break ; }if (token->special =='[' &&lookup_type (token->next)) {
@@ -665,7 +663,6 @@ static struct token *unary_expression(struct token *token, struct expression **t unary =alloc_expression (token->pos,EXPR_PREOP ); unary->op = token->special; unary->unop = unop; - unary->flags =expr_flags_decay_consts (unop->flags); *tree = unary;return next; }
validation/constexpr-preop.c new file +29 -0
@@ -0,0 +1,29 @@ +static int a[] = { + [+0 ] =0 ,// OK + [+__builtin_choose_expr (0 ,0 ,0 )] =0 ,// OK + [+0. ] =0 ,// KO + [+__builtin_choose_expr (0 ,0 ,0. )] =0 ,// KO + [-0 ] =0 ,// OK + [-__builtin_choose_expr (0 ,0 ,0 )] =0 ,// OK + [-0. ] =0 ,// KO + [-__builtin_choose_expr (0 ,0 ,0. )] =0 ,// KO + [~0 ] =0 ,// OK + [~__builtin_choose_expr (0 ,0 ,0 )] =0 ,// OK + [!0 ] =0 ,// OK + [!__builtin_choose_expr (0 ,0 ,0 )] =0 ,// OK + [!0. ] =0 ,// KO + [!__builtin_choose_expr (0 ,0 ,0. )] =0 ,// KO +}; + +/* +* check-name: Expression constness propagation in preops +* +* check-error-start +constexpr-preop.c:4:5: error: bad constant expression +constexpr-preop.c:5:33: error: bad constant expression +constexpr-preop.c:8:4: error: bad constant expression +constexpr-preop.c:9:4: error: bad constant expression +constexpr-preop.c:14:4: error: bad integer constant expression +constexpr-preop.c:15:4: error: bad integer constant expression +* check-error-end +*/
Signature · 1 line
2.4.5