Fix pr 17276.

See the description here:
https://sourceware.org/ml/gdb-patches/2014-08/msg00283.html

This patch keeps track of whether the current line has seen a
non-zero discriminator, and if so coalesces consecutive entries
for the same line (by ignoring all entries after the first).

gdb/ChangeLog:

	PR 17276
	* dwarf2read.c (dwarf_record_line_p): New function.
	(dwarf_decode_lines_1): Ignore subsequent line number entries
	for the same line if any entry had a non-zero discriminator.

gdb/testsuite/ChangeLog:

	* gdb.dwarf2/dw2-single-line-discriminators.S: New file.
	* gdb.dwarf2/dw2-single-line-discriminators.c: New file.
	* gdb.dwarf2/dw2-single-line-discriminators.exp: New file.

1 files changed, 31 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dwarf2/dw2-single-line-discriminators.c b/gdb/testsuite/gdb.dwarf2/dw2-single-line-discriminators.c
new file mode 100644
index 00000000000..5e0f7fb0815
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-single-line-discriminators.c
@@ -0,0 +1,31 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2014 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int x;
+
+int
+main ()
+{
+  int i;
+
+  /* Ensure runto_main stops before the for loop.  */
+  x = 0;
+
+  for (i = 0; i < 10; ++i) continue; /* stepi line */
+
+  return 0;
+}