c++: Fix location for -Wunused-macros [PR66290]

Message ID 62328b0cdbdd374fdca89723306c34331d0531fa.1659015329.git.lhyatt@gmail.com
State New, archived
Headers
Series c++: Fix location for -Wunused-macros [PR66290] |

Commit Message

Lewis Hyatt July 28, 2022, 2:01 p.m. UTC
  In C++, since all tokens are lexed from libcpp up front, diagnostics generated
by libcpp after lexing has completed do not get a valid location from libcpp
(rather, libcpp thinks they all pertain to the end of the file.) This has long
been addressed using the global variable "done_lexing", which the C++ frontend
sets at the appropriate time; when done_lexing is true, then c_cpp_diagnostic(),
which outputs libcpp's diagnostics, uses input_location instead of the wrong
libcpp location. The C++ frontend arranges that input_location will point to the
token it is currently processing, so this generally works fine. However, there
is one exception currently, which is -Wunused-macros. This gets generated at the
end of processing in cpp_finish (), since we need to wait until then to
determine whether a macro was eventually used or not. But the locations it
passes to c_cpp_diagnostic () were remembered from the original lexing and hence
they should not be overridden with input_location, which is now the one
incorrectly pointing to the end of the file.

Fixed by setting done_lexing=false again just prior to calling cpp_finish (). I
also renamed the variable from done_lexing to "override_libcpp_locations", since
it's now not strictly about lexing anymore.

There is no new testcase with this patch, since we already had an xfailed
testcase which is now fixed.

gcc/c-family/ChangeLog:

	PR c++/66290
	* c-common.h: Rename global done_lexing to
	override_libcpp_locations.
	* c-common.cc (c_cpp_diagnostic): Likewise.
	* c-opts.cc (c_common_finish): Set override_libcpp_locations
	(formerly done_lexing) immediately prior to calling cpp_finish ().

gcc/cp/ChangeLog:

	PR c++/66290
	* parser.cc (cp_lexer_new_main): Rename global done_lexing to
	override_libcpp_locations.

gcc/testsuite/ChangeLog:

	PR c++/66290
	* c-c++-common/pragma-diag-15.c: Remove xfail for C++.
---

Notes:
    Hello-
    
    The attached patch fixes PR66290, which is about C++ diagnostics using
    the wrong location for -Wunused-macros. Please let me know if it looks OK?
    
    Bootstrap + regtest all languages on x86-64 linux looks good, no changes other
    than the un-XFAILed testcases.
    
    Thank you!
    
    -Lewis

 gcc/c-family/c-common.cc                    | 10 ++++++----
 gcc/c-family/c-common.h                     |  8 +++++---
 gcc/c-family/c-opts.cc                      |  6 ++++++
 gcc/cp/parser.cc                            |  2 +-
 gcc/testsuite/c-c++-common/pragma-diag-15.c |  2 +-
 5 files changed, 19 insertions(+), 9 deletions(-)
  

Comments

Jeff Law July 30, 2022, 7:59 p.m. UTC | #1
On 7/28/2022 8:01 AM, Lewis Hyatt via Gcc-patches wrote:
> In C++, since all tokens are lexed from libcpp up front, diagnostics generated
> by libcpp after lexing has completed do not get a valid location from libcpp
> (rather, libcpp thinks they all pertain to the end of the file.) This has long
> been addressed using the global variable "done_lexing", which the C++ frontend
> sets at the appropriate time; when done_lexing is true, then c_cpp_diagnostic(),
> which outputs libcpp's diagnostics, uses input_location instead of the wrong
> libcpp location. The C++ frontend arranges that input_location will point to the
> token it is currently processing, so this generally works fine. However, there
> is one exception currently, which is -Wunused-macros. This gets generated at the
> end of processing in cpp_finish (), since we need to wait until then to
> determine whether a macro was eventually used or not. But the locations it
> passes to c_cpp_diagnostic () were remembered from the original lexing and hence
> they should not be overridden with input_location, which is now the one
> incorrectly pointing to the end of the file.
>
> Fixed by setting done_lexing=false again just prior to calling cpp_finish (). I
> also renamed the variable from done_lexing to "override_libcpp_locations", since
> it's now not strictly about lexing anymore.
>
> There is no new testcase with this patch, since we already had an xfailed
> testcase which is now fixed.
>
> gcc/c-family/ChangeLog:
>
> 	PR c++/66290
> 	* c-common.h: Rename global done_lexing to
> 	override_libcpp_locations.
> 	* c-common.cc (c_cpp_diagnostic): Likewise.
> 	* c-opts.cc (c_common_finish): Set override_libcpp_locations
> 	(formerly done_lexing) immediately prior to calling cpp_finish ().
>
> gcc/cp/ChangeLog:
>
> 	PR c++/66290
> 	* parser.cc (cp_lexer_new_main): Rename global done_lexing to
> 	override_libcpp_locations.
>
> gcc/testsuite/ChangeLog:
>
> 	PR c++/66290
> 	* c-c++-common/pragma-diag-15.c: Remove xfail for C++.
Ewww.  But OK.
Jeff
  

Patch

diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
index 655c3aefee6..6e41ceb38e9 100644
--- a/gcc/c-family/c-common.cc
+++ b/gcc/c-family/c-common.cc
@@ -284,9 +284,11 @@  int c_inhibit_evaluation_warnings;
    be generated.  */
 bool in_late_binary_op;
 
-/* Whether lexing has been completed, so subsequent preprocessor
-   errors should use the compiler's input_location.  */
-bool done_lexing = false;
+/* Depending on which phase of processing we are in, we may need
+   to prefer input_location to libcpp's locations.  (Specifically,
+   after the C++ lexer is done lexing tokens, but prior to calling
+   cpp_finish (), we need to do so.  */
+bool override_libcpp_locations;
 
 /* Information about how a function name is generated.  */
 struct fname_var_t
@@ -6681,7 +6683,7 @@  c_cpp_diagnostic (cpp_reader *pfile ATTRIBUTE_UNUSED,
     default:
       gcc_unreachable ();
     }
-  if (done_lexing)
+  if (override_libcpp_locations)
     richloc->set_range (0, input_location, SHOW_RANGE_WITH_CARET);
   diagnostic_set_info_translated (&diagnostic, msg, ap,
 				  richloc, dlevel);
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index f9064393b4e..c06769b6f0b 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -767,10 +767,12 @@  extern int max_tinst_depth;
 
 extern int c_inhibit_evaluation_warnings;
 
-/* Whether lexing has been completed, so subsequent preprocessor
-   errors should use the compiler's input_location.  */
+/* Depending on which phase of processing we are in, we may need
+   to prefer input_location to libcpp's locations.  (Specifically,
+   after the C++ lexer is done lexing tokens, but prior to calling
+   cpp_finish (), we need to do so.  */
 
-extern bool done_lexing;
+extern bool override_libcpp_locations;
 
 /* C types are partitioned into three subsets: object, function, and
    incomplete types.  */
diff --git a/gcc/c-family/c-opts.cc b/gcc/c-family/c-opts.cc
index b9f01a65ed7..4e1463689de 100644
--- a/gcc/c-family/c-opts.cc
+++ b/gcc/c-family/c-opts.cc
@@ -1281,6 +1281,12 @@  c_common_finish (void)
 	}
     }
 
+  /* When we call cpp_finish (), it may generate some diagnostics using
+     locations it remembered from the preprocessing phase, e.g. for
+     -Wunused-macros.  So inform c_cpp_diagnostic () not to override those
+     locations with input_location, which would be incorrect now.  */
+  override_libcpp_locations = false;
+
   /* For performance, avoid tearing down cpplib's internal structures
      with cpp_destroy ().  */
   cpp_finish (parse_in, deps_stream);
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 4f67441eeb1..66e6fde3e28 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -755,7 +755,7 @@  cp_lexer_new_main (void)
 
   /* Subsequent preprocessor diagnostics should use compiler
      diagnostic functions to get the compiler source location.  */
-  done_lexing = true;
+  override_libcpp_locations = true;
 
   maybe_check_all_macros (parse_in);
 
diff --git a/gcc/testsuite/c-c++-common/pragma-diag-15.c b/gcc/testsuite/c-c++-common/pragma-diag-15.c
index d8076b4f93a..8ffff88d5e3 100644
--- a/gcc/testsuite/c-c++-common/pragma-diag-15.c
+++ b/gcc/testsuite/c-c++-common/pragma-diag-15.c
@@ -9,5 +9,5 @@ 
    because the location of the macro definition is incorrectly set.  This is a
    separate issue, will resolve it in a later patch.  */
 
-#define X /* { dg-warning "-:-Wunused-macros" {} { xfail c++ } } */
+#define X /* { dg-warning "-:-Wunused-macros" } */
 #pragma GCC diagnostic ignored "-Wunused-macros"