[gcc r13-3887] c-family: Support #pragma region/endregion [PR85487]

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:d3fe767c16e7c528e4fc71c8a68ac14b4573d880

commit r13-3887-gd3fe767c16e7c528e4fc71c8a68ac14b4573d880
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Nov 9 21:49:52 2022 +0000

    c-family: Support #pragma region/endregion [PR85487]
    
    These pragmas are used by some editors to mark regions of code for
    grouping and folding. GCC should silently ignore them, rather than
    giving -Wunknown-pragmas warnings.
    
            PR c/85487
    
    gcc/ChangeLog:
    
            * doc/cpp/pragmas.rst (Pragmas): Document region pragmas.
    
    gcc/c-family/ChangeLog:
    
            * c-pragma.cc (handle_pragma_ignore): New function.
            (init_pragma): Register region and endregion pragmas.
    
    gcc/testsuite/ChangeLog:
    
            * c-c++-common/pragma-region.c: New test.

Diff:
---
 gcc/c-family/c-pragma.cc                   |  9 +++++++++
 gcc/doc/cpp/pragmas.rst                    |  3 +++
 gcc/testsuite/c-c++-common/pragma-region.c | 11 +++++++++++
 3 files changed, 23 insertions(+)

diff --git a/gcc/c-family/c-pragma.cc b/gcc/c-family/c-pragma.cc
index b5a4b3c970f..142a46441ac 100644
--- a/gcc/c-family/c-pragma.cc
+++ b/gcc/c-family/c-pragma.cc
@@ -1403,6 +1403,12 @@ handle_pragma_message (cpp_reader *)
 	    TREE_STRING_POINTER (message));
 }
 
+/* Ignore a no-op pragma that GCC recognizes, but which has no effect.  */
+static void
+handle_pragma_ignore (cpp_reader *)
+{
+}
+
 /* Mark whether the current location is valid for a STDC pragma.  */
 
 static bool valid_location_for_stdc_pragma;
@@ -1870,6 +1876,9 @@ init_pragma (void)
   c_register_pragma ("GCC", "pop_options", handle_pragma_pop_options);
   c_register_pragma ("GCC", "reset_options", handle_pragma_reset_options);
 
+  c_register_pragma (0, "region", handle_pragma_ignore);
+  c_register_pragma (0, "endregion", handle_pragma_ignore);
+
   c_register_pragma ("STDC", "FLOAT_CONST_DECIMAL64",
 		     handle_pragma_float_const_decimal64);
 
diff --git a/gcc/doc/cpp/pragmas.rst b/gcc/doc/cpp/pragmas.rst
index da07cebf4a1..78277d7b623 100644
--- a/gcc/doc/cpp/pragmas.rst
+++ b/gcc/doc/cpp/pragmas.rst
@@ -119,3 +119,6 @@ GCC plugins may provide their own pragmas.
   file will never be read again, no matter what.  It is a less-portable
   alternative to using :samp:`#ifndef` to guard the contents of header files
   against multiple inclusions.
+
+``#pragma region {tokens}...``, ``#pragma endregion {tokens}...``
+  These pragmas are accepted, but have no effect.
diff --git a/gcc/testsuite/c-c++-common/pragma-region.c b/gcc/testsuite/c-c++-common/pragma-region.c
new file mode 100644
index 00000000000..8e0cbe1f16f
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pragma-region.c
@@ -0,0 +1,11 @@
+/* { dg-options "-Wunknown-pragmas" } */
+/* { dg-final { scan-assembler "code_within_region" } } */
+/* { dg-final { scan-assembler "code_within_named_region" } } */
+
+#pragma region
+void code_within_region() { }
+#pragma endregion
+
+#pragma region ignored name
+void code_within_named_region() { }
+#pragma endregion // ignored comment