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.

4 files changed, 368 insertions, 0 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 08ee2b9..a006ed5 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2014-08-22  Doug Evans  <dje@google.com>
+
+	PR 17276
+	* 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.
+
 2014-08-22  Yao Qi  <yao@codesourcery.com>
 
 	* gdb.python/py-finish-breakpoint.exp: Copy .py file to host.
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-single-line-discriminators.S b/gdb/testsuite/gdb.dwarf2/dw2-single-line-discriminators.S
new file mode 100644
index 0000000..a9fa63e
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-single-line-discriminators.S
@@ -0,0 +1,281 @@
+/* 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/>.  */
+
+/* This was made from dw2-single-line-discriminators.c using
+	clang -dA -S -g
+   and then hand-editing the assembly a bit (simplify paths,
+   tweak so gas accepts it).  */
+
+	.text
+	.file	"dw2-single-line-discriminators.c"
+	.section	.debug_info,"",@progbits
+.Lsection_info:
+	.section	.debug_abbrev,"",@progbits
+.Lsection_abbrev:
+	.section	.debug_line,"",@progbits
+.Lsection_line:
+	.section	.debug_pubnames,"",@progbits
+	.section	.debug_pubtypes,"",@progbits
+	.section	.debug_str,"MS",@progbits,1
+.Linfo_string:
+	.section	.debug_loc,"",@progbits
+.Lsection_debug_loc:
+	.section	.debug_ranges,"",@progbits
+.Ldebug_range:
+	.file	1 "gdb.dwarf2/dw2-single-line-discriminators.c"
+	.text
+	.globl	main
+	.align	16, 0x90
+	.type	main,@function
+main:                                   # @main
+.Lfunc_begin0:
+	.loc	1 22 0                  # dw2-single-line-discriminators.c:22:0
+	.cfi_startproc
+# BB#0:
+	pushq	%rbp
+.Ltmp0:
+	.cfi_def_cfa_offset 16
+.Ltmp1:
+	.cfi_offset %rbp, -16
+	movq	%rsp, %rbp
+.Ltmp2:
+	.cfi_def_cfa_register %rbp
+	movl	$0, -4(%rbp)
+	.loc	1 26 3 prologue_end     # dw2-single-line-discriminators.c:26:3
+.Ltmp3:
+	movl	$0, x
+	.loc	1 28 8                  # dw2-single-line-discriminators.c:28:8
+.Ltmp4:
+	movl	$0, -8(%rbp)
+.LBB0_1:                                # =>This Inner Loop Header: Depth=1
+	.loc	1 28 8 discriminator 4  # dw2-single-line-discriminators.c:28:8
+.Ltmp5:
+	cmpl	$10, -8(%rbp)
+	jge	.LBB0_4
+.Ltmp6:
+# BB#2:                                 #   in Loop: Header=BB0_1 Depth=1
+	.loc	1 28 28 discriminator 2 # dw2-single-line-discriminators.c:28:28
+	jmp	.LBB0_3
+.Ltmp7:
+.LBB0_3:                                #   in Loop: Header=BB0_1 Depth=1
+	.loc	1 28 23 discriminator 3 # dw2-single-line-discriminators.c:28:23
+	movl	-8(%rbp), %eax
+	addl	$1, %eax
+	movl	%eax, -8(%rbp)
+	jmp	.LBB0_1
+.Ltmp8:
+.LBB0_4:
+	movl	$0, %eax
+	.loc	1 30 3                  # dw2-single-line-discriminators.c:30:3
+	popq	%rbp
+	retq
+.Ltmp9:
+.Ltmp10:
+	.size	main, .Ltmp10-main
+.Lfunc_end0:
+	.cfi_endproc
+
+	.type	x,@object               # @x
+	.comm	x,4,4
+.Ldebug_end1:
+	.section	.debug_str,"MS",@progbits,1
+.Linfo_string0:
+	.asciz	"clang version (trunk r215195)"
+.Linfo_string1:
+	.asciz	"dw2-single-line-discriminators.c"
+.Linfo_string2:
+	.asciz	"/tmp/obj/gdb/testsuite"
+.Linfo_string3:
+	.asciz	"x"
+.Linfo_string4:
+	.asciz	"int"
+.Linfo_string5:
+	.asciz	"main"
+.Linfo_string6:
+	.asciz	"i"
+	.section	.debug_info,"",@progbits
+.L.debug_info_begin0:
+	.long	108                     # Length of Unit
+	.short	4                       # DWARF version number
+	.long	.Lsection_abbrev        # Offset Into Abbrev. Section
+	.byte	8                       # Address Size (in bytes)
+	.byte	1                       # Abbrev [1] 0xb:0x65 DW_TAG_compile_unit
+	.long	.Linfo_string0          # DW_AT_producer
+	.short	12                      # DW_AT_language
+	.long	.Linfo_string1          # DW_AT_name
+	.long	.Lline_table_start0     # DW_AT_stmt_list
+	.long	.Linfo_string2          # DW_AT_comp_dir
+	.quad	.Lfunc_begin0           # DW_AT_low_pc
+.Lset0 = .Lfunc_end0-.Lfunc_begin0      # DW_AT_high_pc
+	.long	.Lset0
+	.byte	2                       # Abbrev [2] 0x2a:0x15 DW_TAG_variable
+	.long	.Linfo_string3          # DW_AT_name
+	.long	63                      # DW_AT_type
+                                        # DW_AT_external
+	.byte	1                       # DW_AT_decl_file
+	.byte	18                      # DW_AT_decl_line
+	.byte	9                       # DW_AT_location
+	.byte	3
+	.quad	x
+	.byte	3                       # Abbrev [3] 0x3f:0x7 DW_TAG_base_type
+	.long	.Linfo_string4          # DW_AT_name
+	.byte	5                       # DW_AT_encoding
+	.byte	4                       # DW_AT_byte_size
+	.byte	4                       # Abbrev [4] 0x46:0x29 DW_TAG_subprogram
+	.quad	.Lfunc_begin0           # DW_AT_low_pc
+.Lset1 = .Lfunc_end0-.Lfunc_begin0      # DW_AT_high_pc
+	.long	.Lset1
+	.byte	1                       # DW_AT_frame_base
+	.byte	86
+	.long	.Linfo_string5          # DW_AT_name
+	.byte	1                       # DW_AT_decl_file
+	.byte	21                      # DW_AT_decl_line
+	.long	63                      # DW_AT_type
+                                        # DW_AT_external
+	.byte	1                       # DW_AT_accessibility
+                                        # DW_ACCESS_public
+	.byte	5                       # Abbrev [5] 0x60:0xe DW_TAG_variable
+	.byte	2                       # DW_AT_location
+	.byte	145
+	.byte	120
+	.long	.Linfo_string6          # DW_AT_name
+	.byte	1                       # DW_AT_decl_file
+	.byte	23                      # DW_AT_decl_line
+	.long	63                      # DW_AT_type
+	.byte	0                       # End Of Children Mark
+	.byte	0                       # End Of Children Mark
+.L.debug_info_end0:
+	.section	.debug_abbrev,"",@progbits
+	.byte	1                       # Abbreviation Code
+	.byte	17                      # DW_TAG_compile_unit
+	.byte	1                       # DW_CHILDREN_yes
+	.byte	37                      # DW_AT_producer
+	.byte	14                      # DW_FORM_strp
+	.byte	19                      # DW_AT_language
+	.byte	5                       # DW_FORM_data2
+	.byte	3                       # DW_AT_name
+	.byte	14                      # DW_FORM_strp
+	.byte	16                      # DW_AT_stmt_list
+	.byte	23                      # DW_FORM_sec_offset
+	.byte	27                      # DW_AT_comp_dir
+	.byte	14                      # DW_FORM_strp
+	.byte	17                      # DW_AT_low_pc
+	.byte	1                       # DW_FORM_addr
+	.byte	18                      # DW_AT_high_pc
+	.byte	6                       # DW_FORM_data4
+	.byte	0                       # EOM(1)
+	.byte	0                       # EOM(2)
+	.byte	2                       # Abbreviation Code
+	.byte	52                      # DW_TAG_variable
+	.byte	0                       # DW_CHILDREN_no
+	.byte	3                       # DW_AT_name
+	.byte	14                      # DW_FORM_strp
+	.byte	73                      # DW_AT_type
+	.byte	19                      # DW_FORM_ref4
+	.byte	63                      # DW_AT_external
+	.byte	25                      # DW_FORM_flag_present
+	.byte	58                      # DW_AT_decl_file
+	.byte	11                      # DW_FORM_data1
+	.byte	59                      # DW_AT_decl_line
+	.byte	11                      # DW_FORM_data1
+	.byte	2                       # DW_AT_location
+	.byte	24                      # DW_FORM_exprloc
+	.byte	0                       # EOM(1)
+	.byte	0                       # EOM(2)
+	.byte	3                       # Abbreviation Code
+	.byte	36                      # DW_TAG_base_type
+	.byte	0                       # DW_CHILDREN_no
+	.byte	3                       # DW_AT_name
+	.byte	14                      # DW_FORM_strp
+	.byte	62                      # DW_AT_encoding
+	.byte	11                      # DW_FORM_data1
+	.byte	11                      # DW_AT_byte_size
+	.byte	11                      # DW_FORM_data1
+	.byte	0                       # EOM(1)
+	.byte	0                       # EOM(2)
+	.byte	4                       # Abbreviation Code
+	.byte	46                      # DW_TAG_subprogram
+	.byte	1                       # DW_CHILDREN_yes
+	.byte	17                      # DW_AT_low_pc
+	.byte	1                       # DW_FORM_addr
+	.byte	18                      # DW_AT_high_pc
+	.byte	6                       # DW_FORM_data4
+	.byte	64                      # DW_AT_frame_base
+	.byte	24                      # DW_FORM_exprloc
+	.byte	3                       # DW_AT_name
+	.byte	14                      # DW_FORM_strp
+	.byte	58                      # DW_AT_decl_file
+	.byte	11                      # DW_FORM_data1
+	.byte	59                      # DW_AT_decl_line
+	.byte	11                      # DW_FORM_data1
+	.byte	73                      # DW_AT_type
+	.byte	19                      # DW_FORM_ref4
+	.byte	63                      # DW_AT_external
+	.byte	25                      # DW_FORM_flag_present
+	.byte	50                      # DW_AT_accessibility
+	.byte	11                      # DW_FORM_data1
+	.byte	0                       # EOM(1)
+	.byte	0                       # EOM(2)
+	.byte	5                       # Abbreviation Code
+	.byte	52                      # DW_TAG_variable
+	.byte	0                       # DW_CHILDREN_no
+	.byte	2                       # DW_AT_location
+	.byte	24                      # DW_FORM_exprloc
+	.byte	3                       # DW_AT_name
+	.byte	14                      # DW_FORM_strp
+	.byte	58                      # DW_AT_decl_file
+	.byte	11                      # DW_FORM_data1
+	.byte	59                      # DW_AT_decl_line
+	.byte	11                      # DW_FORM_data1
+	.byte	73                      # DW_AT_type
+	.byte	19                      # DW_FORM_ref4
+	.byte	0                       # EOM(1)
+	.byte	0                       # EOM(2)
+	.byte	0                       # EOM(3)
+	.section	.debug_ranges,"",@progbits
+	.section	.debug_loc,"",@progbits
+	.section	.debug_pubnames,"",@progbits
+.Lset2 = .LpubNames_end0-.LpubNames_begin0 # Length of Public Names Info
+	.long	.Lset2
+.LpubNames_begin0:
+	.short	2                       # DWARF Version
+	.long	.L.debug_info_begin0    # Offset of Compilation Unit Info
+.Lset3 = .L.debug_info_end0-.L.debug_info_begin0 # Compilation Unit Length
+	.long	.Lset3
+	.long	70                      # DIE offset
+	.asciz	"main"                  # External Name
+	.long	42                      # DIE offset
+	.asciz	"x"                     # External Name
+	.long	0                       # End Mark
+.LpubNames_end0:
+	.section	.debug_pubtypes,"",@progbits
+.Lset4 = .LpubTypes_end0-.LpubTypes_begin0 # Length of Public Types Info
+	.long	.Lset4
+.LpubTypes_begin0:
+	.short	2                       # DWARF Version
+	.long	.L.debug_info_begin0    # Offset of Compilation Unit Info
+.Lset5 = .L.debug_info_end0-.L.debug_info_begin0 # Compilation Unit Length
+	.long	.Lset5
+	.long	63                      # DIE offset
+	.asciz	"int"                   # External Name
+	.long	0                       # End Mark
+.LpubTypes_end0:
+
+	.ident	"clang version (trunk r215195)"
+	.section	".note.GNU-stack","",@progbits
+	.section	.debug_line,"",@progbits
+.Lline_table_start0:
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 0000000..5e0f7fb
--- /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;
+}
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 0000000..dbd9438
--- /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\[ \t\]+\[^\r\n\]+"