Re: C++ PATCH for C++17 constexpr if

[Jason Merrill <jason@redhat.com>]

[-- Attachment #1: Type: text/plain, Size: 445 bytes --]

On Wed, Aug 10, 2016 at 5:57 PM, Jason Merrill <jason@redhat.com> wrote:
> This patch implements the C++17 constexpr if feature.  The primary use
> is in templates, where the non-taken branch of the constexpr
> if-statement is not instantiated.  But it can also be used outside of
> templates, where the branches are parsed and discarded, and discarded
> return statements are not used for return type deduction.

...and the feature test macro.

[-- Attachment #2: cx-if-macro.diff --]
[-- Type: text/plain, Size: 1231 bytes --]

commit 1f20a739d61ef839ec7091aa1278adf6d726ead4
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Aug 10 18:35:01 2016 -0400

    	* c-cppbuiltin.c (c_cpp_builtins): Define __cpp_if_constexpr.

diff --git a/gcc/c-family/c-cppbuiltin.c b/gcc/c-family/c-cppbuiltin.c
index 46c70ac..82ed19d 100644
--- a/gcc/c-family/c-cppbuiltin.c
+++ b/gcc/c-family/c-cppbuiltin.c
@@ -882,6 +882,7 @@ c_cpp_builtins (cpp_reader *pfile)
 	  cpp_define (pfile, "__cpp_nontype_template_args=201411");
 	  cpp_define (pfile, "__cpp_range_based_for=201603");
 	  cpp_define (pfile, "__cpp_constexpr=201603");
+	  cpp_define (pfile, "__cpp_if_constexpr=201606");
 	}
       if (flag_concepts)
 	/* Use a value smaller than the 201507 specified in
diff --git a/gcc/testsuite/g++.dg/cpp1z/feat-cxx1z.C b/gcc/testsuite/g++.dg/cpp1z/feat-cxx1z.C
index f5ed6ab..41b6111 100644
--- a/gcc/testsuite/g++.dg/cpp1z/feat-cxx1z.C
+++ b/gcc/testsuite/g++.dg/cpp1z/feat-cxx1z.C
@@ -344,6 +344,12 @@
 #  error "__cpp_hex_float != 201603"
 #endif
 
+#ifndef __cpp_if_constexpr
+#  error "__cpp_if_constexpr"
+#elif __cpp_if_constexpr != 201606
+#  error "__cpp_if_constexpr != 201606"
+#endif
+
 #ifdef __has_cpp_attribute
 
 #  if ! __has_cpp_attribute(maybe_unused)