[libcpp] Disable cb.line_change callbacks from within cpp_peek_token (PR preprocessor/61977)

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

This is one possible way to fix another problem with the contextual macros.
When preprocessing e.g. vector at the end of line (both with -mno-altivec
and -maltivec), we cpp_peek_token at least the next token, and unfortunately
during the peek we already call pfile->cb.line_change hook.  So we get
int y; \n
emitted at that point, then e.g. when vector isn't expanded, we notice the
current print.src_line is wrong for the token and thus emit
\n## 5 "pr61977-1.c"\n       vector
and then when actually calling cpp_get_token_1 on the next token we emit
the newline again from another pfile->cb.line_change hook.

I believe we really should never call cb.line_change hook from within
cpp_peek_token, the tokens are re-added to lookaheads and will be processed
by _cpp_lex_token again at some point.

Below is one possible fix for that, another option is introduce another
pfile->state or pfile field for that, or another option would be to
pass some flag from cpp_peek_token down to _cpp_lex_token.
As cpp_peek_token is used very rarely, right now only in:
1) the contextual builtin macro stuff (powerpc*/spu only)
2) in __has_attribute/__has_cpp_attribute implementation
3) in genmatch build utility
the attached patch, while perhaps not the cleanest, has the advantage of not
affecting the more often used code path that might be performance critical.

Ok for trunk if it passes testing on powerpc64{,le}-linux and
{x86_64,i686}-linux?

2015-04-01  Jakub Jelinek  <jakub@redhat.com>

	PR preprocessor/61977
	* lex.c (cpp_peek_token): Temporarily clear pfile->cb.line_change.

	* gcc.target/powerpc/pr61977-1.c: New test.
	* gcc.target/powerpc/pr61977-2.c: New test.

--- libcpp/lex.c.jj	2015-03-31 19:39:28.000000000 +0200
+++ libcpp/lex.c	2015-04-01 12:03:31.146846380 +0200
@@ -2080,6 +2080,12 @@ cpp_peek_token (cpp_reader *pfile, int i
   count = index;
   pfile->keep_tokens++;
 
+  /* For peeked tokens temporarily disable line_change reporting,
+     until the tokens are parsed for real.  */
+  void (*line_change) (cpp_reader *, const cpp_token *, int)
+    = pfile->cb.line_change;
+  pfile->cb.line_change = NULL;
+
   do
     {
       peektok = _cpp_lex_token (pfile);
@@ -2093,6 +2099,7 @@ cpp_peek_token (cpp_reader *pfile, int i
 
   _cpp_backup_tokens_direct (pfile, count - index);
   pfile->keep_tokens--;
+  pfile->cb.line_change = line_change;
 
   return peektok;
 }
--- gcc/testsuite/gcc.target/powerpc/pr61977-1.c.jj	2015-04-01 12:15:15.341311939 +0200
+++ gcc/testsuite/gcc.target/powerpc/pr61977-1.c	2015-04-01 12:17:32.030102843 +0200
@@ -0,0 +1,8 @@
+/* PR preprocessor/61977 */
+/* { dg-do preprocess } */
+/* { dg-options "-mno-altivec -mno-vsx" } */
+
+int y; vector
+int x;
+
+/* { dg-final { scan-file "pr61977-1.i" "(^|\\n)int y; vector\\n" } } */
--- gcc/testsuite/gcc.target/powerpc/pr61977-2.c.jj	2015-04-01 12:15:18.125266339 +0200
+++ gcc/testsuite/gcc.target/powerpc/pr61977-2.c	2015-04-01 12:18:22.033321600 +0200
@@ -0,0 +1,8 @@
+/* PR preprocessor/61977 */
+/* { dg-do preprocess } */
+/* { dg-options "-maltivec" } */
+
+int y; vector
+int x;
+
+/* { dg-final { scan-file "pr61977-2.i" "(^|\\n)int y; __attribute__\\(\\(altivec\\(vector__\\)\\)\\)\\n" } } */

	Jakub