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PATCH c++/19628 (take 2)

From: Matt Austern <matt at lafstern dot org>
To: GCC Patches <gcc-patches at gcc dot gnu dot org>
Date: Sun, 30 Jan 2005 11:19:55 -0800
Subject: PATCH c++/19628 (take 2)

This patch reenables accepting __builtin_constant_p in constant-expressions. I don't believe there was a good reason, or even a deliberate decision, to prohibit it.

There may be other builtins that we want to allow in constant-expressions. If so, this patch will make it easy to add them as desired.

OK to commit to mainline?

--Matt

* cp-tree.h (builtin_is_constant_p): Declare. * tree.c (builtin_is_constant_p): New function. * parser.c (cp_parser_postfix_expression): Allow function call in constant expression if it's a builtin for which builtin_is_constant_p returns true. * semantics.c (finish_id_expression): Likewise. * g++.dg/ext/builtin7.C: New test.

Index: gcc/cp/cp-tree.h =================================================================== RCS file: /cvs/gcc/gcc/gcc/cp/cp-tree.h,v retrieving revision 1.1097 diff -p -r1.1097 cp-tree.h *** gcc/cp/cp-tree.h 20 Jan 2005 07:12:49 -0000 1.1097 --- gcc/cp/cp-tree.h 30 Jan 2005 19:04:41 -0000 *************** extern tree copy_binfo (tree, tree, t *** 4204,4209 **** --- 4204,4210 ---- tree *, int); extern int member_p (tree); extern cp_lvalue_kind real_lvalue_p (tree); + extern bool builtin_is_constant_p (tree); extern tree build_min (enum tree_code, tree, ...); extern tree build_min_nt (enum tree_code, ...); extern tree build_min_non_dep (enum tree_code, tree, ...); Index: gcc/cp/parser.c =================================================================== RCS file: /cvs/gcc/gcc/gcc/cp/parser.c,v retrieving revision 1.304 diff -p -r1.304 parser.c *** gcc/cp/parser.c 29 Jan 2005 02:07:05 -0000 1.304 --- gcc/cp/parser.c 30 Jan 2005 19:04:41 -0000 *************** cp_parser_postfix_expression (cp_parser *** 3988,3995 ****

/* Function calls are not permitted in constant-expressions. */ ! if (cp_parser_non_integral_constant_expression (parser, ! "a function call")) { postfix_expression = error_mark_node; break; --- 3988,3996 ----

/* Function calls are not permitted in constant-expressions. */ ! if (! builtin_is_constant_p (postfix_expression) ! && cp_parser_non_integral_constant_expression (parser, ! "a function call")) { postfix_expression = error_mark_node; break; Index: gcc/cp/semantics.c =================================================================== RCS file: /cvs/gcc/gcc/gcc/cp/semantics.c,v retrieving revision 1.458 diff -p -r1.458 semantics.c *** gcc/cp/semantics.c 27 Jan 2005 07:32:25 -0000 1.458 --- gcc/cp/semantics.c 30 Jan 2005 19:04:41 -0000 *************** finish_id_expression (tree id_expression *** 2658,2664 **** expression. Enumerators and template parameters have already been handled above. */ if (integral_constant_expression_p ! && !DECL_INTEGRAL_CONSTANT_VAR_P (decl)) { if (!allow_non_integral_constant_expression_p) { --- 2658,2665 ---- expression. Enumerators and template parameters have already been handled above. */ if (integral_constant_expression_p ! && ! DECL_INTEGRAL_CONSTANT_VAR_P (decl) ! && ! builtin_is_constant_p (decl)) { if (!allow_non_integral_constant_expression_p) { Index: gcc/cp/tree.c =================================================================== RCS file: /cvs/gcc/gcc/gcc/cp/tree.c,v retrieving revision 1.425 diff -p -r1.425 tree.c *** gcc/cp/tree.c 18 Jan 2005 23:51:26 -0000 1.425 --- gcc/cp/tree.c 30 Jan 2005 19:04:47 -0000 *************** lvalue_p (tree ref) *** 215,220 **** --- 215,234 ---- (lvalue_p_1 (ref, /*class rvalue ok*/ 1) != clk_none); }

+ /* Test whether DECL is a builtin that may appear in a + constant-expression. */ + + bool + builtin_is_constant_p (tree decl) + { + /* At present BUILT_IN_CONSTANT_P is the only builtin we're allowing + in constant-expressions. We may want to add other builtins later. */ + return TREE_CODE (decl) == FUNCTION_DECL + && DECL_BUILT_IN_CLASS (decl) == BUILT_IN_NORMAL + && DECL_FUNCTION_CODE (decl) == BUILT_IN_CONSTANT_P; + } + + /* Build a TARGET_EXPR, initializing the DECL with the VALUE. */

static tree cvs diff: gcc/testsuite/g++.dg/ext/builtin7.C is a new entry, no comparison available [isolde:fsf]$ cvs -z3 diff -pN Index: gcc/cp/cp-tree.h =================================================================== RCS file: /cvs/gcc/gcc/gcc/cp/cp-tree.h,v retrieving revision 1.1097 diff -p -r1.1097 cp-tree.h *** gcc/cp/cp-tree.h 20 Jan 2005 07:12:49 -0000 1.1097 --- gcc/cp/cp-tree.h 30 Jan 2005 19:06:29 -0000 *************** extern tree copy_binfo (tree, tree, t *** 4204,4209 **** --- 4204,4210 ---- tree *, int); extern int member_p (tree); extern cp_lvalue_kind real_lvalue_p (tree); + extern bool builtin_is_constant_p (tree); extern tree build_min (enum tree_code, tree, ...); extern tree build_min_nt (enum tree_code, ...); extern tree build_min_non_dep (enum tree_code, tree, ...); Index: gcc/cp/parser.c =================================================================== RCS file: /cvs/gcc/gcc/gcc/cp/parser.c,v retrieving revision 1.304 diff -p -r1.304 parser.c *** gcc/cp/parser.c 29 Jan 2005 02:07:05 -0000 1.304 --- gcc/cp/parser.c 30 Jan 2005 19:06:29 -0000 *************** cp_parser_postfix_expression (cp_parser *** 3988,3995 ****

/* Function calls are not permitted in constant-expressions. */ ! if (cp_parser_non_integral_constant_expression (parser, ! "a function call")) { postfix_expression = error_mark_node; break; --- 3988,3996 ----

/* Function calls are not permitted in constant-expressions. */ ! if (! builtin_is_constant_p (postfix_expression) ! && cp_parser_non_integral_constant_expression (parser, ! "a function call")) { postfix_expression = error_mark_node; break; Index: gcc/cp/semantics.c =================================================================== RCS file: /cvs/gcc/gcc/gcc/cp/semantics.c,v retrieving revision 1.458 diff -p -r1.458 semantics.c *** gcc/cp/semantics.c 27 Jan 2005 07:32:25 -0000 1.458 --- gcc/cp/semantics.c 30 Jan 2005 19:06:29 -0000 *************** finish_id_expression (tree id_expression *** 2658,2664 **** expression. Enumerators and template parameters have already been handled above. */ if (integral_constant_expression_p ! && !DECL_INTEGRAL_CONSTANT_VAR_P (decl)) { if (!allow_non_integral_constant_expression_p) { --- 2658,2665 ---- expression. Enumerators and template parameters have already been handled above. */ if (integral_constant_expression_p ! && ! DECL_INTEGRAL_CONSTANT_VAR_P (decl) ! && ! builtin_is_constant_p (decl)) { if (!allow_non_integral_constant_expression_p) { Index: gcc/cp/tree.c =================================================================== RCS file: /cvs/gcc/gcc/gcc/cp/tree.c,v retrieving revision 1.425 diff -p -r1.425 tree.c *** gcc/cp/tree.c 18 Jan 2005 23:51:26 -0000 1.425 --- gcc/cp/tree.c 30 Jan 2005 19:06:33 -0000 *************** lvalue_p (tree ref) *** 215,220 **** --- 215,234 ---- (lvalue_p_1 (ref, /*class rvalue ok*/ 1) != clk_none); }

+ /* Test whether DECL is a builtin that may appear in a + constant-expression. */ + + bool + builtin_is_constant_p (tree decl) + { + /* At present BUILT_IN_CONSTANT_P is the only builtin we're allowing + in constant-expressions. We may want to add other builtins later. */ + return TREE_CODE (decl) == FUNCTION_DECL + && DECL_BUILT_IN_CLASS (decl) == BUILT_IN_NORMAL + && DECL_FUNCTION_CODE (decl) == BUILT_IN_CONSTANT_P; + } + + /* Build a TARGET_EXPR, initializing the DECL with the VALUE. */

static tree Index: gcc/testsuite/g++.dg/ext/builtin7.C =================================================================== RCS file: gcc/testsuite/g++.dg/ext/builtin7.C diff -N gcc/testsuite/g++.dg/ext/builtin7.C *** /dev/null 1 Jan 1970 00:00:00 -0000 --- gcc/testsuite/g++.dg/ext/builtin7.C 30 Jan 2005 19:06:35 -0000 *************** *** 0 **** --- 1,14 ---- + // PR c++/19628 + // Verify that __builtin_constant_p may appear in a constant-expression. + + // { dg-do run } + + int main() + { + switch (3) { + case (__builtin_constant_p(7) ? 3 : 8): + return 0; + default: + return 1; + } + }

Follow-Ups:
- Re: PATCH c++/19628 (take 2)
  - From: Roger Sayle

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