Re: PATCH to _cpp_backup_tokens

Re: PATCH to _cpp_backup_tokens

[Neil Booth]

Jason Merrill wrote:-

> We don't want to back up to the previous hunk until we actually need
> something from it; it might not exist.  Fixes compilation of preprocessed
> code with no # lines.
> 
> 2001-11-19  Jason Merrill  <jason@redhat.com>
> 
> 	* cppmacro.c (_cpp_backup_tokens): Pop cur_run before decrementing
> 	cur_token, not after.

This is not correct.  cpplib maintains cur_token as being a pointer
just past the current token; as it is post-incremented.  This is the
simplest implementation for many reasons, but the variable is poorly
named I guess.  So your patch would give incorrect diagnostic
locations and / or segfaults in some cases; see e.g. the diagnostic
reporting code in cpperror.c.  Also, your patch should have contained
a testcase.

Correct patch + testcase below; I'll commit them when a bootstrap has
completed.

Neil.

	* cppmacro.c (_cpp_backup_tokens): Revert previous check-in.
	Don't fall off the base token run.
	* gcc.dg/cpp/fpreprocessed.c: New test case.

Index: cppmacro.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/cppmacro.c,v
retrieving revision 1.84
diff -u -p -r1.84 cppmacro.c
--- cppmacro.c	2001/11/19 11:28:47	1.84
+++ cppmacro.c	2001/11/19 18:50:53
@@ -1087,12 +1087,14 @@ _cpp_backup_tokens (pfile, count)
       pfile->lookaheads += count;
       while (count--)
 	{
-	  if (pfile->cur_token == pfile->cur_run->base)
+	  pfile->cur_token--;
+	  if (pfile->cur_token == pfile->cur_run->base
+	      /* Possible with -fpreprocessed and no leading #line.  */
+	      && pfile->cur_run->prev != NULL)
 	    {
 	      pfile->cur_run = pfile->cur_run->prev;
 	      pfile->cur_token = pfile->cur_run->limit;
 	    }
-	  pfile->cur_token--;
 	}
     }
   else
Index: testsuite/gcc.dg/cpp/fpreprocessed.c
===================================================================
RCS file: fpreprocessed.c
diff -N fpreprocessed.c
--- /dev/null	Tue May  5 13:32:27 1998
+++ fpreprocessed.c	Mon Nov 19 10:50:53 2001
@@ -0,0 +1,10 @@
+/* Copyright (C) 2001 Free Software Foundation, Inc.  */
+
+/* { dg-do preprocess } */
+/* { dg-options -fpreprocessed } */
+
+/* Source: Jason Merrill, 19 Nov 2001.  We'd try and back up a token
+   and move to a non-existent token run with -fpreprocessed on a file
+   without a leading # line.  */
+
+foo

PATCH to _cpp_backup_tokens

[Jason Merrill]

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We don't want to back up to the previous hunk until we actually need
something from it; it might not exist.  Fixes compilation of preprocessed
code with no # lines.

2001-11-19  Jason Merrill  <jason@redhat.com>

	* cppmacro.c (_cpp_backup_tokens): Pop cur_run before decrementing
	cur_token, not after.


[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
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*** cppmacro.c.~1~	Mon Nov 19 11:19:05 2001
--- cppmacro.c	Sat Nov 17 10:43:30 2001
*************** _cpp_backup_tokens (pfile, count)
*** 1087,1098 ****
        pfile->lookaheads += count;
        while (count--)
  	{
- 	  pfile->cur_token--;
  	  if (pfile->cur_token == pfile->cur_run->base)
  	    {
  	      pfile->cur_run = pfile->cur_run->prev;
  	      pfile->cur_token = pfile->cur_run->limit;
  	    }
  	}
      }
    else
--- 1087,1098 ----
        pfile->lookaheads += count;
        while (count--)
  	{
  	  if (pfile->cur_token == pfile->cur_run->base)
  	    {
  	      pfile->cur_run = pfile->cur_run->prev;
  	      pfile->cur_token = pfile->cur_run->limit;
  	    }
+ 	  pfile->cur_token--;
  	}
      }
    else