PR symtab/15691

	* dwarf2read.c (struct dwarf2_per_cu_data): New member tu_read.
	(fill_in_sig_entry_from_dwo_entry): Reorganize asserts.
	Add assert of sig_entry->dwo_unit == NULL.
	(lookup_dwo_signatured_type): Don't assign TU to a DWO if the TU
	had already been read.
	(read_signatured_type): Set per_cu.tu_read.

	testsuite/
	* gdb.dwarf2/fission-mix.exp: New file.
	* gdb.dwarf2/fission-mix.h: New file.
	* gdb.dwarf2/fission-mix.c: New file.
	* gdb.dwarf2/fission-mix2.c: New file.

7 files changed, 176 insertions, 14 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index ff22280..0888348 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,13 @@
 2013-08-01  Doug Evans  <dje@google.com>
 
+	PR symtab/15691
+	* dwarf2read.c (struct dwarf2_per_cu_data): New member tu_read.
+	(fill_in_sig_entry_from_dwo_entry): Reorganize asserts.
+	Add assert of sig_entry->dwo_unit == NULL.
+	(lookup_dwo_signatured_type): Don't assign TU to a DWO if the TU
+	had already been read.
+	(read_signatured_type): Set per_cu.tu_read.
+
 	PR symtab/15695
 	* valops.c (value_struct_elt): Add missing call to check_typedef.
 	(value_find_oload_method_list): Ditto.
diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 241c83e..cb77386 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -558,6 +558,16 @@ struct dwarf2_per_cu_data
      attributes in the stub.  */
   unsigned int reading_dwo_directly : 1;
 
+  /* Non-zero if the TU has been read.
+     This is used to assist the "Stay in DWO Optimization" for Fission:
+     When reading a DWO, it's faster to read TUs from the DWO instead of
+     fetching them from random other DWOs (due to comdat folding).
+     If the TU has already been read, the optimization is unnecessary
+     (and unwise - we don't want to change where gdb thinks the TU lives
+     "midflight").
+     This flag is only valid if is_debug_types is true.  */
+  unsigned int tu_read : 1;
+
   /* The section this CU/TU lives in.
      If the DIE refers to a DWO file, this is always the original die,
      not the DWO file.  */
@@ -4443,11 +4453,7 @@ fill_in_sig_entry_from_dwo_entry (struct objfile *objfile,
 				  struct signatured_type *sig_entry,
 				  struct dwo_unit *dwo_entry)
 {
-  sig_entry->per_cu.section = dwo_entry->section;
-  sig_entry->per_cu.offset = dwo_entry->offset;
-  sig_entry->per_cu.length = dwo_entry->length;
-  sig_entry->per_cu.reading_dwo_directly = 1;
-  sig_entry->per_cu.objfile = objfile;
+  /* Make sure we're not clobbering something we don't expect to.  */
   gdb_assert (! sig_entry->per_cu.queued);
   gdb_assert (sig_entry->per_cu.cu == NULL);
   gdb_assert (sig_entry->per_cu.v.quick != NULL);
@@ -4455,19 +4461,26 @@ fill_in_sig_entry_from_dwo_entry (struct objfile *objfile,
   gdb_assert (sig_entry->signature == dwo_entry->signature);
   gdb_assert (sig_entry->type_offset_in_section.sect_off == 0);
   gdb_assert (sig_entry->type_unit_group == NULL);
+  gdb_assert (sig_entry->dwo_unit == NULL);
+
+  sig_entry->per_cu.section = dwo_entry->section;
+  sig_entry->per_cu.offset = dwo_entry->offset;
+  sig_entry->per_cu.length = dwo_entry->length;
+  sig_entry->per_cu.reading_dwo_directly = 1;
+  sig_entry->per_cu.objfile = objfile;
   sig_entry->type_offset_in_tu = dwo_entry->type_offset_in_tu;
   sig_entry->dwo_unit = dwo_entry;
 }
 
 /* Subroutine of lookup_signatured_type.
-   Create the signatured_type data structure for a TU to be read in
-   directly from a DWO file, bypassing the stub.
-   We do this for the case where there is no DWP file and we're using
-   .gdb_index: When reading a CU we want to stay in the DWO file containing
-   that CU.  Otherwise we could end up reading several other DWO files (due
-   to comdat folding) to process the transitive closure of all the mentioned
-   TUs, and that can be slow.  The current DWO file will have every type
-   signature that it needs.
+   If we haven't read the TU yet, create the signatured_type data structure
+   for a TU to be read in directly from a DWO file, bypassing the stub.
+   This is the "Stay in DWO Optimization": When there is no DWP file and we're
+   using .gdb_index, then when reading a CU we want to stay in the DWO file
+   containing that CU.  Otherwise we could end up reading several other DWO
+   files (due to comdat folding) to process the transitive closure of all the
+   mentioned TUs, and that can be slow.  The current DWO file will have every
+   type signature that it needs.
    We only do this for .gdb_index because in the psymtab case we already have
    to read all the DWOs to build the type unit groups.  */
 
@@ -4496,8 +4509,13 @@ lookup_dwo_signatured_type (struct dwarf2_cu *cu, ULONGEST sig)
   sig_entry = htab_find (dwarf2_per_objfile->signatured_types, &find_sig_entry);
   if (sig_entry == NULL)
     return NULL;
+
+  /* We can get here with the TU already read, *or* in the process of being
+     read.  Don't reassign it if that's the case.  Also note that if the TU is
+     already being read, it may not have come from a DWO, the program may be
+     a mix of Fission-compiled code and non-Fission-compiled code.  */
   /* Have we already tried to read this TU?  */
-  if (sig_entry->dwo_unit != NULL)
+  if (sig_entry->per_cu.tu_read)
     return sig_entry;
 
   /* Ok, this is the first time we're reading this TU.  */
@@ -18608,6 +18626,7 @@ read_signatured_type (struct signatured_type *sig_type)
 
   init_cutu_and_read_dies (per_cu, NULL, 0, 1,
 			   read_signatured_type_reader, NULL);
+  sig_type->per_cu.tu_read = 1;
 }
 
 /* Decode simple location descriptions.
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index e3b0683..25a1b01 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,11 @@
 2013-08-01  Doug Evans  <dje@google.com>
 
+	PR symtab/15691
+	* gdb.dwarf2/fission-mix.exp: New file.
+	* gdb.dwarf2/fission-mix.h: New file.
+	* gdb.dwarf2/fission-mix.c: New file.
+	* gdb.dwarf2/fission-mix2.c: New file.
+
 	PR symtab/15695
 	* gdb.base/func-ptr.exp: New file.
 	* gdb.base/func-ptr.c: New file.
diff --git a/gdb/testsuite/gdb.dwarf2/fission-mix.c b/gdb/testsuite/gdb.dwarf2/fission-mix.c
new file mode 100644
index 0000000..c8fdde2
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/fission-mix.c
@@ -0,0 +1,33 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2013 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/>.  */
+
+#include "fission-mix.h"
+
+struct s foo;
+
+int
+func (int arg)
+{
+  return arg + 1;
+}
+
+int
+main ()
+{
+  foo.x = 1;
+  return func (-1);
+}
diff --git a/gdb/testsuite/gdb.dwarf2/fission-mix.exp b/gdb/testsuite/gdb.dwarf2/fission-mix.exp
new file mode 100644
index 0000000..3a1090f
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/fission-mix.exp
@@ -0,0 +1,46 @@
+# Copyright 2013 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/>.
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2.
+if ![dwarf2_support] {
+    return 0  
+}
+
+standard_testfile fission-mix.c fission-mix2.c
+set objfile [standard_output_file ${testfile}.o]
+set objfile2 [standard_output_file ${testfile}2.o]
+
+# Compile fission-mix.c without Fission and fission-mix2.c with Fission.
+if { [gdb_compile ${srcdir}/${subdir}/${srcfile} $objfile object {debug}] != "" } {
+    return -1
+}
+if { [gdb_compile ${srcdir}/${subdir}/${srcfile2} $objfile2 object {debug additional_flags=-gsplit-dwarf}] != "" } {
+    return -1
+}
+if {[gdb_compile "$objfile $objfile2" $binfile executable {debug}] != "" } {
+    return -1
+}
+
+clean_restart $binfile
+
+gdb_test "break main" "Breakpoint .*"
+
+# Bug 15691: gdb would crash here on an assert violation.
+# The debug info for the TU for "struct s" has already been read,
+# but gdb doesn't think so.
+# To repro the bug, --target_board=dwarf4-gdb-index, or equivalent, is needed.
+gdb_test "break func2" "Breakpoint .*"
diff --git a/gdb/testsuite/gdb.dwarf2/fission-mix.h b/gdb/testsuite/gdb.dwarf2/fission-mix.h
new file mode 100644
index 0000000..2521e68
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/fission-mix.h
@@ -0,0 +1,23 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2013 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/>.  */
+
+/* A type to be recorded as a DW_TAG_type_unit.  */
+
+struct s
+{
+  int x;
+};
diff --git a/gdb/testsuite/gdb.dwarf2/fission-mix2.c b/gdb/testsuite/gdb.dwarf2/fission-mix2.c
new file mode 100644
index 0000000..a9194fa
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/fission-mix2.c
@@ -0,0 +1,27 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2013 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/>.  */
+
+#include "fission-mix.h"
+
+struct s bar;
+
+int
+func2 ()
+{
+  bar.x = 1;
+  return 42;
+}