Hi! cpp_peek_token is broken whenever it sees CPP_EOF, as it doesn't back up the previous tokens (if any) and the CPP_EOF token, so for callers of cpp_peek_token whenever it returns CPP_EOF it is a fatal condition, so one really can't peek safely.
cpp_peek_token has apparently been written for the conditional macros where it really assumes one can safely peek tokens several times. The following patch fixes that. If no CPP_EOF is seen or it is seen on the last token, index will be -1 and thus count - index is still count + 1 as before, but if we hit CPP_EOF earlier, we only back up tokens before that. Richard and Prathamesh raised this issue already some time ago: https://gcc.gnu.org/ml/gcc-patches/2014-08/msg00895.html but there was no follow-up on that. Bootstrapped/regtested on powerpc64{,le}-linux and {x86_64,i686}-linux, ok for trunk? 2015-03-31 Jakub Jelinek <ja...@redhat.com> PR preprocessor/61977 * lex.c (cpp_peek_token): If peektok is CPP_EOF, back it up with all tokens peeked by the current function. --- libcpp/lex.c.jj 2015-03-17 18:10:12.000000000 +0100 +++ libcpp/lex.c 2015-03-31 19:39:28.207748285 +0200 @@ -2084,11 +2084,14 @@ cpp_peek_token (cpp_reader *pfile, int i { peektok = _cpp_lex_token (pfile); if (peektok->type == CPP_EOF) - return peektok; + { + index--; + break; + } } while (index--); - _cpp_backup_tokens_direct (pfile, count + 1); + _cpp_backup_tokens_direct (pfile, count - index); pfile->keep_tokens--; return peektok; --- gcc/testsuite/gcc.dg/cpp/pr61977.c.jj 2015-03-31 19:46:12.226279905 +0200 +++ gcc/testsuite/gcc.dg/cpp/pr61977.c 2015-03-31 19:46:03.638417398 +0200 @@ -0,0 +1,4 @@ +/* PR preprocessor/61977 */ +/* { dg-do preprocess } */ + +vector Jakub
