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, 49 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dwarf2/dw2-single-line-discriminators.exp b/gdb/testsuite/gdb.dwarf2/dw2-single-line-discriminators.exp
new file mode 100644
index 00000000000..dbd9438a350
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-single-line-discriminators.exp
@@ -0,0 +1,49 @@
+# Copyright 2012-2014 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/>.
+
+# Test gdb's coalescing of multiple line number entries for the same line
+# but with different discriminators.  PR 17276.
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if ![dwarf2_support] {
+    return 0  
+}
+
+# This test can only be run on x86-64 targets.
+if {![istarget x86_64-*] || ![is_lp64_target]} {
+    return 0
+}
+
+standard_testfile .S
+set csrcfile ${testfile}.c
+
+if { [prepare_for_testing "${testfile}.exp" "${testfile}" $srcfile {nodebug}] } {
+    return -1
+}
+
+if ![runto_main] then {
+    fail "Cannot run to main."
+    continue
+}
+
+set srcline [gdb_get_line_number "stepi line" $csrcfile]
+gdb_breakpoint $srcline
+gdb_continue_to_breakpoint "stepi line"
+
+# A stepi will land us in the middle of the line, and thus
+# gdb should print the pc value.
+gdb_test "stepi" "$hex\[ \t\]+$srcline\[ \t\]+\[^\r\n\]+"