[Version 4][PATCH][gcc][PR94230]provide an option to change the size limitation for -Wmisleading-indent

[Qing Zhao <QING.ZHAO@ORACLE.COM>]

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Hi, Dave,

Thanks a lot for the review and comments.
I just updated the patch with all your suggestions, bootstrapped it and run regression test, no any issue.

The newest patch is attached with this email.

Richard/Jakub, please advise on whether I can commit this patch to Gcc10?

Thanks a lot.

Qing

gcc/c-family/ChangeLog:

2020-04-24  qing zhao  <qing.zhao@oracle.com>

        * c-indentation.c (get_visual_column): Add a hint to use the new
        -flarge-source-files option.

gcc/ChangeLog:

2020-04-24  qing zhao  <qing.zhao@oracle.com>

        * common.opt: Add -flarge-source-files.
        * doc/invoke.texi: Document it.
        * toplev.c (process_options): Set line_table->default_range_bits
        to 0 when flag_large_source_files is true.


gcc/testsuite/ChangeLog:

2020-04-24  qing zhao  <qing.zhao@oracle.com>

        * gcc.dg/plugin/location-overflow-test-1.c (fn_1): New message to
        verify that hint about -flarge-source-files is emitted.


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From 512a8ccce1e6ed8889cd7144459c130935abf0de Mon Sep 17 00:00:00 2001
From: qing zhao <qing.zhao@oracle.com>
Date: Fri, 24 Apr 2020 16:50:18 +0200
Subject: [PATCH] Fix PR94230

---
 gcc/c-family/c-indentation.c                          |  5 +++++
 gcc/common.opt                                        |  5 +++++
 gcc/doc/invoke.texi                                   | 19 +++++++++++++++++--
 .../gcc.dg/plugin/location-overflow-test-1.c          |  2 +-
 gcc/toplev.c                                          |  3 +++
 5 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/gcc/c-family/c-indentation.c b/gcc/c-family/c-indentation.c
index f737555db0e..baa506347cd 100644
--- a/gcc/c-family/c-indentation.c
+++ b/gcc/c-family/c-indentation.c
@@ -67,6 +67,11 @@ get_visual_column (expanded_location exploc, location_t loc,
 		  "%<-Wmisleading-indentation%> is disabled from this point"
 		  " onwards, since column-tracking was disabled due to"
 		  " the size of the code/headers");
+	  if (!flag_large_source_files)
+	    inform (loc,
+		    "adding %<-flarge-source-files%> will allow for more" 
+		    " column-tracking support, at the expense of compilation"
+		    " and memory");
 	}
       return false;
     }
diff --git a/gcc/common.opt b/gcc/common.opt
index d33383b523c..30d05734d16 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -1609,6 +1609,11 @@ fkeep-gc-roots-live
 Common Undocumented Report Var(flag_keep_gc_roots_live) Optimization
 ; Always keep a pointer to a live memory block
 
+flarge-source-files
+Common Report Var(flag_large_source_files) Init(0)
+Improve GCC's ability to track column numbers in large source files,
+at the expense of slower compilation.
+
 floop-parallelize-all
 Common Report Var(flag_loop_parallelize_all) Optimization
 Mark all loops as parallel.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index a37a2ee9c19..bdde7c1d881 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -574,8 +574,8 @@ Objective-C and Objective-C++ Dialects}.
 -dD  -dI  -dM  -dN  -dU @gol
 -fdebug-cpp  -fdirectives-only  -fdollars-in-identifiers  @gol
 -fexec-charset=@var{charset}  -fextended-identifiers  @gol
--finput-charset=@var{charset}  -fmacro-prefix-map=@var{old}=@var{new}  @gol
--fmax-include-depth=@var{depth} @gol
+-finput-charset=@var{charset}  -flarge-source-files  @gol
+-fmacro-prefix-map=@var{old}=@var{new} -fmax-include-depth=@var{depth} @gol
 -fno-canonical-system-headers  -fpch-deps  -fpch-preprocess  @gol
 -fpreprocessed  -ftabstop=@var{width}  -ftrack-macro-expansion  @gol
 -fwide-exec-charset=@var{charset}  -fworking-directory @gol
@@ -14183,6 +14183,21 @@ This option may be useful in conjunction with the @option{-B} or
 perform additional processing of the program source between
 normal preprocessing and compilation.
 
+@item -flarge-source-files
+@opindex flarge-source-files
+Adjust GCC to expect large source files, at the expense of slower
+compilation and higher memory usage.
+
+Specifically, GCC normally tracks both column numbers and line numbers
+within source files and it normally prints both of these numbers in
+diagnostics.  However, once it has processed a certain number of source
+lines, it stops tracking column numbers and only tracks line numbers.
+This means that diagnostics for later lines do not include column numbers.
+It also means that options like @option{-Wmisleading-indentation} cease to work
+at that point, although the compiler prints a note if this happens.
+Passing @option{-flarge-source-files} significantly increases the number
+of source lines that GCC can process before it stops tracking columns.
+
 @end table
 
 @node Assembler Options
diff --git a/gcc/testsuite/gcc.dg/plugin/location-overflow-test-1.c b/gcc/testsuite/gcc.dg/plugin/location-overflow-test-1.c
index 1a80a668a0f..a3ac12d3b46 100644
--- a/gcc/testsuite/gcc.dg/plugin/location-overflow-test-1.c
+++ b/gcc/testsuite/gcc.dg/plugin/location-overflow-test-1.c
@@ -13,7 +13,7 @@ int
 fn_1 (int flag)
 {
   int x = 4, y = 5;
-  if (flag) x = 3; y = 2; /* { dg-message "-:disabled from this point" } */
+  if (flag) x = 3; y = 2; /* { dg-message "-:disabled from this point" "adding '-flarge-source-files'" } */
   return x * y;
 }
 
diff --git a/gcc/toplev.c b/gcc/toplev.c
index 4c8be502c71..b3230b71b9d 100644
--- a/gcc/toplev.c
+++ b/gcc/toplev.c
@@ -1854,6 +1854,9 @@ process_options (void)
     hash_table_sanitize_eq_limit
       = param_hash_table_verification_limit;
 
+  if (flag_large_source_files)
+    line_table->default_range_bits = 0;
+
   /* Please don't change global_options after this point, those changes won't
      be reflected in optimization_{default,current}_node.  */
 }
-- 
2.11.0

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> On Apr 23, 2020, at 5:13 PM, David Malcolm <dmalcolm@redhat.com> wrote:
> 
> On Thu, 2020-04-23 at 16:05 -0500, Qing Zhao wrote:
> 
>> Hi, Richard,
>> 
>> This is the 3rd version of the patch, updated based on your previous comments.
> 
> Thanks for working on this, and to Richard for the useful comments.
> 
>> Please take a look at it and let me know whether it’s okay to commit?
> 
> I like the overall approach.
> 
> Some nits inline.
> 
> 
> Maybe: "Verify that hint about -flarge-source-files is emitted".
> 
> 
>> +	  if (!flag_large_source_files)
>> +	    inform (loc,
>> +		    "please add %<-flarge-source-files%> to invoke more" 
>> +		    " column-tracking for large source files");
> 
> It's great having a hint here, but I don't love the wording of the
> hint.
> 
> Maybe reword to:
> 
> "adding %<-flarge-source-files%> will allow for more column-tracking
> support, at the expense of compilation time and memory".
> 
> or somesuch.
> 
>> +This means that diagnostics for later lines do not include column numbers.
>> +It also means that options like @option{-Wmisleading-indent} cease to work
>                                           ^^^^^^^^^^^^^^^^^^^
> This should be:                            -Wmisleading-indentation
> 
>> +at that point, although the compiler prints a note if this happens.
>> +Passing @option{-flarge-source-files} significantly increases the number
>> +of source lines that GCC can process before it stops tracking column.
>                                                                 ^^^^^^
> This should be:							 columns
> 
>> +  if (flag) x = 3; y = 2; /* { dg-message "-:disabled from this point" "add '-flarge-source-files'" } */
> 
> May need updating to match the hint message.
> 
> [...]
> 
> This is OK for stage 1 with those nits fixed.
> 
> There was talk earlier in the thread about fixing this in GCC 10.
> 
> Richi/Jakub: is this OK for stage 4?   Although it adds a new command-
> line option, it's a workaround for a regression introduced in GCC 6 and
> should be low risk.
> 
> Thanks
> Dave
>