[LVU] Introduce location views

This patch introduces an option to enable the generation of location
views along with location lists.  The exact format depends on the
DWARF version: it can be a separate attribute (DW_AT_GNU_locviews) or
(DW_LLE_view_pair) entries in DWARF5+ loclists.

Line number tables are also affected.  If the assembler is found, at
compiler build time, to support .loc views, we use them and
assembler-computed view labels, otherwise we output compiler-generated
line number programs with conservatively-computed view labels.  In
either case, we output view information next to line number changes
when verbose assembly output is requested.

This patch requires an LVU patch that modifies the exported API of
final_scan_insn.  It also expects the entire SFN patchset to be
installed first, although SFN is not a requirement for LVU.

for  include/ChangeLog

	* dwarf2.def (DW_AT_GNU_locviews): New.
	* dwarf2.h (enum dwarf_location_list_entry_type): Add
	DW_LLE_GNU_view_pair.
	(DW_LLE_view_pair): Define.

for  gcc/ChangeLog

	* common.opt (gvariable-location-views): New.
	(gvariable-location-views=incompat5): New.
	* config.in: Rebuilt.
	* configure: Rebuilt.
	* configure.ac: Test assembler for view support.
	* dwarf2asm.c (dw2_asm_output_symname_uleb128): New.
	* dwarf2asm.h (dw2_asm_output_symname_uleb128): Declare.
	* dwarf2out.c (var_loc_view): New typedef.
	(struct dw_loc_list_struct): Add vl_symbol, vbegin, vend.
	(dwarf2out_locviews_in_attribute): New.
	(dwarf2out_locviews_in_loclist): New.
	(dw_val_equal_p): Compare val_view_list of dw_val_class_view_lists.
	(enum dw_line_info_opcode): Add LI_adv_address.
	(struct dw_line_info_table): Add view.
	(RESET_NEXT_VIEW, RESETTING_VIEW_P): New macros.
	(DWARF2_ASM_VIEW_DEBUG_INFO): Define default.
	(zero_view_p): New variable.
	(ZERO_VIEW_P): New macro.
	(output_asm_line_debug_info): New.
	(struct var_loc_node): Add view.
	(add_AT_view_list, AT_loc_list): New.
	(add_var_loc_to_decl): Add view param.  Test it against last.
	(new_loc_list): Add view params.  Record them.
	(AT_loc_list_ptr): Handle loc and view lists.
	(view_list_to_loc_list_val_node): New.
	(print_dw_val): Handle dw_val_class_view_list.
	(size_of_die): Likewise.
	(value_format): Likewise.
	(loc_list_has_views): New.
	(gen_llsym): Set vl_symbol too.
	(maybe_gen_llsym, skip_loc_list_entry): New.
	(dwarf2out_maybe_output_loclist_view_pair): New.
	(output_loc_list): Output view list or entries too.
	(output_view_list_offset): New.
	(output_die): Handle dw_val_class_view_list.
	(output_dwarf_version): New.
	(output_compilation_unit_header): Use it.
	(output_skeleton_debug_sections): Likewise.
	(output_rnglists, output_line_info): Likewise.
	(output_pubnames, output_aranges): Update version comments.
	(output_one_line_info_table): Output view numbers in asm comments.
	(dw_loc_list): Determine current endview, pass it to new_loc_list.
	Call maybe_gen_llsym.
	(loc_list_from_tree_1): Adjust.
	(add_AT_location_description): Create view list attribute if
	needed, check it's absent otherwise.
	(convert_cfa_to_fb_loc_list): Adjust.
	(maybe_emit_file): Call output_asm_line_debug_info for test.
	(dwarf2out_var_location): Reset views as needed.  Precompute
	add_var_loc_to_decl args.  Call get_attr_min_length only if we have the
	attribute.  Set view.
	(new_line_info_table): Reset next view.
	(set_cur_line_info_table): Call output_asm_line_debug_info for test.
	(dwarf2out_source_line): Likewise.  Output view resets and labels to
	the assembler, or select appropriate line info opcodes.
	(prune_unused_types_walk_attribs): Handle dw_val_class_view_list.
	(optimize_string_length): Catch it.  Adjust.
	(resolve_addr): Copy vl_symbol along with ll_symbol.  Handle
	dw_val_class_view_list, and remove it if no longer needed.
	(hash_loc_list): Hash view numbers.
	(loc_list_hasher::equal): Compare them.
	(optimize_location_lists): Check whether a view list symbol is
	needed, and whether the locview attribute is present, and
	whether they match.  Remove the locview attribute if no longer
	needed.
	(index_location_lists): Call skip_loc_list_entry for test.
	(dwarf2out_finish): Call output_asm_line_debug_info for test.
	Use output_dwarf_version.
	* dwarf2out.h (enum dw_val_class): Add dw_val_class_view_list.
	(struct dw_val_node): Add val_view_list.
	* final.c (SEEN_NEXT_VIEW): New.
	(set_next_view_needed): New.
	(clear_next_view_needed): New.
	(maybe_output_next_view): New.
	(final_start_function): Rename to...
	(final_start_function_1): ... this.  Take pointer to FIRST,
	add SEEN parameter.  Emit param bindings in the initial view.
	(final_start_function): Reintroduce SEEN-less interface.
	(final): Rename to...
	(final_1): ... this.  Take SEEN parameter.  Output final pending
	next view at the end.
	(final): Reintroduce seen-less interface.
	(final_scan_insn): Output pending next view before switching
	sections or ending a block.  Mark the next view as needed when
	outputting variable locations.  Notify debug backend of section
	changes, and of location view changes.
	(rest_of_handle_final): Adjust.
	* toplev.c (process_options): Autodetect value for debug variable
	location views option.  Warn on incompat5 without -gdwarf-5.
	* doc/invoke.texi (gvariable-location-views): New.
	(gvariable-location-views=incompat5): New.
	(gno-variable-location-views): New.

From-SVN: r257510

gcc/ChangeLog

+2018-02-09  Alexandre Oliva <aoliva@redhat.com>
+
+	* common.opt (gvariable-location-views): New.
+	(gvariable-location-views=incompat5): New.
+	* config.in: Rebuilt.
+	* configure: Rebuilt.
+	* configure.ac: Test assembler for view support.
+	* dwarf2asm.c (dw2_asm_output_symname_uleb128): New.
+	* dwarf2asm.h (dw2_asm_output_symname_uleb128): Declare.
+	* dwarf2out.c (var_loc_view): New typedef.
+	(struct dw_loc_list_struct): Add vl_symbol, vbegin, vend.
+	(dwarf2out_locviews_in_attribute): New.
+	(dwarf2out_locviews_in_loclist): New.
+	(dw_val_equal_p): Compare val_view_list of dw_val_class_view_lists.
+	(enum dw_line_info_opcode): Add LI_adv_address.
+	(struct dw_line_info_table): Add view.
+	(RESET_NEXT_VIEW, RESETTING_VIEW_P): New macros.
+	(DWARF2_ASM_VIEW_DEBUG_INFO): Define default.
+	(zero_view_p): New variable.
+	(ZERO_VIEW_P): New macro.
+	(output_asm_line_debug_info): New.
+	(struct var_loc_node): Add view.
+	(add_AT_view_list, AT_loc_list): New.
+	(add_var_loc_to_decl): Add view param.  Test it against last.
+	(new_loc_list): Add view params.  Record them.
+	(AT_loc_list_ptr): Handle loc and view lists.
+	(view_list_to_loc_list_val_node): New.
+	(print_dw_val): Handle dw_val_class_view_list.
+	(size_of_die): Likewise.
+	(value_format): Likewise.
+	(loc_list_has_views): New.
+	(gen_llsym): Set vl_symbol too.
+	(maybe_gen_llsym, skip_loc_list_entry): New.
+	(dwarf2out_maybe_output_loclist_view_pair): New.
+	(output_loc_list): Output view list or entries too.
+	(output_view_list_offset): New.
+	(output_die): Handle dw_val_class_view_list.
+	(output_dwarf_version): New.
+	(output_compilation_unit_header): Use it.
+	(output_skeleton_debug_sections): Likewise.
+	(output_rnglists, output_line_info): Likewise.
+	(output_pubnames, output_aranges): Update version comments.
+	(output_one_line_info_table): Output view numbers in asm comments.
+	(dw_loc_list): Determine current endview, pass it to new_loc_list.
+	Call maybe_gen_llsym.
+	(loc_list_from_tree_1): Adjust.
+	(add_AT_location_description): Create view list attribute if
+	needed, check it's absent otherwise.
+	(convert_cfa_to_fb_loc_list): Adjust.
+	(maybe_emit_file): Call output_asm_line_debug_info for test.
+	(dwarf2out_var_location): Reset views as needed.  Precompute
+	add_var_loc_to_decl args.  Call get_attr_min_length only if we have the
+	attribute.  Set view.
+	(new_line_info_table): Reset next view.
+	(set_cur_line_info_table): Call output_asm_line_debug_info for test.
+	(dwarf2out_source_line): Likewise.  Output view resets and labels to
+	the assembler, or select appropriate line info opcodes.
+	(prune_unused_types_walk_attribs): Handle dw_val_class_view_list.
+	(optimize_string_length): Catch it.  Adjust.
+	(resolve_addr): Copy vl_symbol along with ll_symbol.  Handle
+	dw_val_class_view_list, and remove it if no longer needed.
+	(hash_loc_list): Hash view numbers.
+	(loc_list_hasher::equal): Compare them.
+	(optimize_location_lists): Check whether a view list symbol is
+	needed, and whether the locview attribute is present, and
+	whether they match.  Remove the locview attribute if no longer
+	needed.
+	(index_location_lists): Call skip_loc_list_entry for test.
+	(dwarf2out_finish): Call output_asm_line_debug_info for test.
+	Use output_dwarf_version.
+	* dwarf2out.h (enum dw_val_class): Add dw_val_class_view_list.
+	(struct dw_val_node): Add val_view_list.
+	* final.c (SEEN_NEXT_VIEW): New.
+	(set_next_view_needed): New.
+	(clear_next_view_needed): New.
+	(maybe_output_next_view): New.
+	(final_start_function): Rename to...
+	(final_start_function_1): ... this.  Take pointer to FIRST,
+	add SEEN parameter.  Emit param bindings in the initial view.
+	(final_start_function): Reintroduce SEEN-less interface.
+	(final): Rename to...
+	(final_1): ... this.  Take SEEN parameter.  Output final pending
+	next view at the end.
+	(final): Reintroduce seen-less interface.
+	(final_scan_insn): Output pending next view before switching
+	sections or ending a block.  Mark the next view as needed when
+	outputting variable locations.  Notify debug backend of section
+	changes, and of location view changes.
+	(rest_of_handle_final): Adjust.
+	* toplev.c (process_options): Autodetect value for debug variable
+	location views option.  Warn on incompat5 without -gdwarf-5.
+	* doc/invoke.texi (gvariable-location-views): New.
+	(gvariable-location-views=incompat5): New.
+	(gno-variable-location-views): New.
+
 2018-02-08  David Malcolm  <dmalcolm@redhat.com>
 
 	PR tree-optimization/84136

gcc/common.opt

@@ -2956,6 +2956,13 @@ gtoggle
 Common Driver Report Var(flag_gtoggle)
 Toggle debug information generation.
 
+gvariable-location-views
+Common Driver Var(debug_variable_location_views, 1) Init(2)
+Augment variable location lists with progressive views.
+
+gvariable-location-views=incompat5
+Common Driver RejectNegative Var(debug_variable_location_views, -1) Init(2)
+
 gvms
 Common Driver JoinedOrMissing Negative(gxcoff)
 Generate debug information in VMS format.

gcc/config.in

@@ -358,6 +358,12 @@
 #endif
 
 
+/* Define if your assembler supports views in dwarf2 .loc directives. */
+#ifndef USED_FOR_TARGET
+#undef HAVE_AS_DWARF2_DEBUG_VIEW
+#endif
+
+
 /* Define if your assembler supports the R_PPC64_ENTRY relocation. */
 #ifndef USED_FOR_TARGET
 #undef HAVE_AS_ENTRY_MARKERS

gcc/configure

@@ -27825,6 +27825,52 @@ $as_echo "$gcc_cv_as_dwarf2_file_buggy" >&6; }
 
 $as_echo "#define HAVE_AS_DWARF2_DEBUG_LINE 1" >>confdefs.h
 
+
+    if test $gcc_cv_as_leb128 = yes; then
+	conftest_s="\
+	.file 1 \"conftest.s\"
+	.loc 1 3 0 view .LVU1
+	$insn
+	.data
+	.uleb128 .LVU1
+	.uleb128 .LVU1
+"
+	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking assembler for dwarf2 debug_view support" >&5
+$as_echo_n "checking assembler for dwarf2 debug_view support... " >&6; }
+if test "${gcc_cv_as_dwarf2_debug_view+set}" = set; then :
+  $as_echo_n "(cached) " >&6
+else
+  gcc_cv_as_dwarf2_debug_view=no
+    if test $in_tree_gas = yes; then
+    if test $in_tree_gas_is_elf = yes \
+  && test $gcc_cv_gas_vers -ge `expr \( \( 2 \* 1000 \) + 27 \) \* 1000 + 0`
+  then gcc_cv_as_dwarf2_debug_view=yes
+fi
+  elif test x$gcc_cv_as != x; then
+    $as_echo "$conftest_s" > conftest.s
+    if { ac_try='$gcc_cv_as $gcc_cv_as_flags  -o conftest.o conftest.s >&5'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; }
+    then
+	gcc_cv_as_dwarf2_debug_view=yes
+    else
+      echo "configure: failed program was" >&5
+      cat conftest.s >&5
+    fi
+    rm -f conftest.o conftest.s
+  fi
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $gcc_cv_as_dwarf2_debug_view" >&5
+$as_echo "$gcc_cv_as_dwarf2_debug_view" >&6; }
+if test $gcc_cv_as_dwarf2_debug_view = yes; then
+
+$as_echo "#define HAVE_AS_DWARF2_DEBUG_VIEW 1" >>confdefs.h
+
+fi
+    fi
  fi
 
  { $as_echo "$as_me:${as_lineno-$LINENO}: checking assembler for --gdwarf2 option" >&5

gcc/configure.ac

@@ -4902,9 +4902,25 @@ if test x"$insn" != x; then
 
  if test $gcc_cv_as_dwarf2_debug_line = yes \
  && test $gcc_cv_as_dwarf2_file_buggy = no; then
-	AC_DEFINE(HAVE_AS_DWARF2_DEBUG_LINE, 1,
+    AC_DEFINE(HAVE_AS_DWARF2_DEBUG_LINE, 1,
   [Define if your assembler supports dwarf2 .file/.loc directives,
    and preserves file table indices exactly as given.])
+
+    if test $gcc_cv_as_leb128 = yes; then
+	conftest_s="\
+	.file 1 \"conftest.s\"
+	.loc 1 3 0 view .LVU1
+	$insn
+	.data
+	.uleb128 .LVU1
+	.uleb128 .LVU1
+"
+	gcc_GAS_CHECK_FEATURE([dwarf2 debug_view support],
+	  gcc_cv_as_dwarf2_debug_view,
+	  [elf,2,27,0],,[$conftest_s],,
+	  [AC_DEFINE(HAVE_AS_DWARF2_DEBUG_VIEW, 1,
+  [Define if your assembler supports views in dwarf2 .loc directives.])])
+    fi
  fi
 
  gcc_GAS_CHECK_FEATURE([--gdwarf2 option],

gcc/doc/invoke.texi

@@ -348,6 +348,7 @@ Objective-C and Objective-C++ Dialects}.
 -gstabs  -gstabs+  -gstrict-dwarf  -gno-strict-dwarf @gol
 -gcolumn-info  -gno-column-info @gol
 -gstatement-frontiers  -gno-statement-frontiers @gol
+-gvariable-location-views  -gno-variable-location-views @gol
 -gvms  -gxcoff  -gxcoff+  -gz@r{[}=@var{type}@r{]} @gol
 -fdebug-prefix-map=@var{old}=@var{new}  -fdebug-types-section @gol
 -fno-eliminate-unused-debug-types @gol
@@ -7255,6 +7256,34 @@ markers in the line number table.  This is enabled by default when
 compiling with optimization (@option{-Os}, @option{-O}, @option{-O2},
 @dots{}), and outputting DWARF 2 debug information at the normal level.
 
+@item -gvariable-location-views
+@item -gvariable-location-views=incompat5
+@item -gno-variable-location-views
+@opindex gvariable-location-views
+@opindex gvariable-location-views=incompat5
+@opindex gno-variable-location-views
+Augment variable location lists with progressive view numbers implied
+from the line number table.  This enables debug information consumers to
+inspect state at certain points of the program, even if no instructions
+associated with the corresponding source locations are present at that
+point.  If the assembler lacks support for view numbers in line number
+tables, this will cause the compiler to emit the line number table,
+which generally makes them somewhat less compact.  The augmented line
+number tables and location lists are fully backward-compatible, so they
+can be consumed by debug information consumers that are not aware of
+these augmentations, but they won't derive any benefit from them either.
+This is enabled by default when outputting DWARF 2 debug information at
+the normal level, as long as @option{-fvar-tracking-assignments} is
+enabled and @option{-gstrict-dwarf} is not.
+
+There is a proposed representation for view numbers that is not backward
+compatible with the location list format introduced in DWARF 5, that can
+be enabled with @option{-gvariable-location-views=incompat5}.  This
+option may be removed in the future, is only provided as a reference
+implementation of the proposed representation.  Debug information
+consumers are not expected to support this extended format, and they
+would be rendered unable to decode location lists using it.
+
 @item -gz@r{[}=@var{type}@r{]}
 @opindex gz
 Produce compressed debug sections in DWARF format, if that is supported.

gcc/dwarf2asm.c

@@ -767,6 +767,35 @@ dw2_asm_output_data_sleb128 (HOST_WIDE_INT value,
   va_end (ap);
 }
 
+/* Output symbol LAB1 as an unsigned LEB128 quantity.  LAB1 should be
+   an assembler-computed constant, e.g. a view number, because we
+   can't have relocations in LEB128 quantities.  */
+
+void
+dw2_asm_output_symname_uleb128 (const char *lab1 ATTRIBUTE_UNUSED,
+				const char *comment, ...)
+{
+  va_list ap;
+
+  va_start (ap, comment);
+
+#ifdef HAVE_AS_LEB128
+  fputs ("\t.uleb128 ", asm_out_file);
+  assemble_name (asm_out_file, lab1);
+#else
+  gcc_unreachable ();
+#endif
+
+  if (flag_debug_asm && comment)
+    {
+      fprintf (asm_out_file, "\t%s ", ASM_COMMENT_START);
+      vfprintf (asm_out_file, comment, ap);
+    }
+  fputc ('\n', asm_out_file);
+
+  va_end (ap);
+}
+
 void
 dw2_asm_output_delta_uleb128 (const char *lab1 ATTRIBUTE_UNUSED,
 			      const char *lab2 ATTRIBUTE_UNUSED,

gcc/dwarf2asm.h

@@ -70,6 +70,10 @@ extern void dw2_asm_output_data_sleb128	(HOST_WIDE_INT,
 					 const char *, ...)
      ATTRIBUTE_NULL_PRINTF_2;
 
+extern void dw2_asm_output_symname_uleb128 (const char *,
+					    const char *, ...)
+     ATTRIBUTE_NULL_PRINTF_2;
+
 extern void dw2_asm_output_delta_uleb128 (const char *, const char *,
 					  const char *, ...)
      ATTRIBUTE_NULL_PRINTF_3;

gcc/dwarf2out.h

@@ -160,7 +160,8 @@ enum dw_val_class
   dw_val_class_discr_list,
   dw_val_class_const_implicit,
   dw_val_class_unsigned_const_implicit,
-  dw_val_class_file_implicit
+  dw_val_class_file_implicit,
+  dw_val_class_view_list
 };
 
 /* Describe a floating point constant value, or a vector constant value.  */
@@ -203,6 +204,7 @@ struct GTY(()) dw_val_node {
       rtx GTY ((tag ("dw_val_class_addr"))) val_addr;
       unsigned HOST_WIDE_INT GTY ((tag ("dw_val_class_offset"))) val_offset;
       dw_loc_list_ref GTY ((tag ("dw_val_class_loc_list"))) val_loc_list;
+      dw_die_ref GTY ((tag ("dw_val_class_view_list"))) val_view_list;
       dw_loc_descr_ref GTY ((tag ("dw_val_class_loc"))) val_loc;
       HOST_WIDE_INT GTY ((default)) val_int;
       unsigned HOST_WIDE_INT

gcc/final.c

@@ -110,6 +110,7 @@ along with GCC; see the file COPYING3.  If not see
 /* Bitflags used by final_scan_insn.  */
 #define SEEN_NOTE	1
 #define SEEN_EMITTED	2
+#define SEEN_NEXT_VIEW	4
 
 /* Last insn processed by final_scan_insn.  */
 static rtx_insn *debug_insn;
@@ -1692,6 +1693,67 @@ get_some_local_dynamic_name ()
   return 0;
 }
 
+/* Arrange for us to emit a source location note before any further
+   real insns or section changes, by setting the SEEN_NEXT_VIEW bit in
+   *SEEN, as long as we are keeping track of location views.  The bit
+   indicates we have referenced the next view at the current PC, so we
+   have to emit it.  This should be called next to the var_location
+   debug hook.  */
+
+static inline void
+set_next_view_needed (int *seen)
+{
+  if (debug_variable_location_views)
+    *seen |= SEEN_NEXT_VIEW;
+}
+
+/* Clear the flag in *SEEN indicating we need to emit the next view.
+   This should be called next to the source_line debug hook.  */
+
+static inline void
+clear_next_view_needed (int *seen)
+{
+  *seen &= ~SEEN_NEXT_VIEW;
+}
+
+/* Test whether we have a pending request to emit the next view in
+   *SEEN, and emit it if needed, clearing the request bit.  */
+
+static inline void
+maybe_output_next_view (int *seen)
+{
+  if ((*seen & SEEN_NEXT_VIEW) != 0)
+    {
+      clear_next_view_needed (seen);
+      (*debug_hooks->source_line) (last_linenum, last_columnnum,
+				   last_filename, last_discriminator,
+				   false);
+    }
+}
+
+/* We want to emit param bindings (before the first begin_stmt) in the
+   initial view, if we are emitting views.  To that end, we may
+   consume initial notes in the function, processing them in
+   final_start_function, before signaling the beginning of the
+   prologue, rather than in final.
+
+   We don't test whether the DECLs are PARM_DECLs: the assumption is
+   that there will be a NOTE_INSN_BEGIN_STMT marker before any
+   non-parameter NOTE_INSN_VAR_LOCATION.  It's ok if the marker is not
+   there, we'll just have more variable locations bound in the initial
+   view, which is consistent with their being bound without any code
+   that would give them a value.  */
+
+static inline bool
+in_initial_view_p (rtx_insn *insn)
+{
+  return (!DECL_IGNORED_P (current_function_decl)
+	  && debug_variable_location_views
+	  && insn && GET_CODE (insn) == NOTE
+	  && (NOTE_KIND (insn) == NOTE_INSN_VAR_LOCATION
+	      || NOTE_KIND (insn) == NOTE_INSN_DELETED));
+}
+
 /* Output assembler code for the start of a function,
    and initialize some of the variables in this file
    for the new function.  The label for the function and associated
@@ -1699,12 +1761,15 @@ get_some_local_dynamic_name ()
 
    FIRST is the first insn of the rtl for the function being compiled.
    FILE is the file to write assembler code to.
+   SEEN should be initially set to zero, and it may be updated to
+   indicate we have references to the next location view, that would
+   require us to emit it at the current PC.
    OPTIMIZE_P is nonzero if we should eliminate redundant
      test and compare insns.  */
 
-void
-final_start_function (rtx_insn *first, FILE *file,
-		      int optimize_p ATTRIBUTE_UNUSED)
+static void
+final_start_function_1 (rtx_insn **firstp, FILE *file, int *seen,
+			int optimize_p ATTRIBUTE_UNUSED)
 {
   block_depth = 0;
 
@@ -1722,8 +1787,21 @@ final_start_function (rtx_insn *first, FILE *file,
   if (flag_sanitize & SANITIZE_ADDRESS)
     asan_function_start ();
 
+  rtx_insn *first = *firstp;
+  if (in_initial_view_p (first))
+    {
+      do
+	{
+	  final_scan_insn (first, file, 0, 0, seen);
+	  first = NEXT_INSN (first);
+	}
+      while (in_initial_view_p (first));
+      *firstp = first;
+    }
+
   if (!DECL_IGNORED_P (current_function_decl))
-    debug_hooks->begin_prologue (last_linenum, last_columnnum, last_filename);
+    debug_hooks->begin_prologue (last_linenum, last_columnnum,
+				 last_filename);
 
   if (!dwarf2_debug_info_emitted_p (current_function_decl))
     dwarf2out_begin_prologue (0, 0, NULL);
@@ -1799,6 +1877,17 @@ final_start_function (rtx_insn *first, FILE *file,
     profile_after_prologue (file);
 }
 
+/* This is an exported final_start_function_1, callable without SEEN.  */
+
+void
+final_start_function (rtx_insn *first, FILE *file,
+		      int optimize_p ATTRIBUTE_UNUSED)
+{
+  int seen = 0;
+  final_start_function_1 (&first, file, &seen, optimize_p);
+  gcc_assert (seen == 0);
+}
+
 static void
 profile_after_prologue (FILE *file ATTRIBUTE_UNUSED)
 {
@@ -1928,11 +2017,10 @@ dump_basic_block_info (FILE *file, rtx_insn *insn, basic_block *start_to_bb,
 /* Output assembler code for some insns: all or part of a function.
    For description of args, see `final_start_function', above.  */
 
-void
-final (rtx_insn *first, FILE *file, int optimize_p)
+static void
+final_1 (rtx_insn *first, FILE *file, int seen, int optimize_p)
 {
   rtx_insn *insn, *next;
-  int seen = 0;
 
   /* Used for -dA dump.  */
   basic_block *start_to_bb = NULL;
@@ -1999,6 +2087,8 @@ final (rtx_insn *first, FILE *file, int optimize_p)
       insn = final_scan_insn (insn, file, optimize_p, 0, &seen);
     }
 
+  maybe_output_next_view (&seen);
+
   if (flag_debug_asm)
     {
       free (start_to_bb);
@@ -2015,6 +2105,23 @@ final (rtx_insn *first, FILE *file, int optimize_p)
 	delete_insn (insn);
     }
 }
+
+/* This is an exported final_1, callable without SEEN.  */
+
+void
+final (rtx_insn *first, FILE *file, int optimize_p)
+{
+  /* Those that use the internal final_start_function_1/final_1 API
+     skip initial debug bind notes in final_start_function_1, and pass
+     the modified FIRST to final_1.  But those that use the public
+     final_start_function/final APIs, final_start_function can't move
+     FIRST because it's not passed by reference, so if they were
+     skipped there, skip them again here.  */
+  while (in_initial_view_p (first))
+    first = NEXT_INSN (first);
+
+  final_1 (first, file, 0, optimize_p);
+}
 
 const char *
 get_insn_template (int code, rtx insn)
@@ -2155,6 +2262,8 @@ final_scan_insn (rtx_insn *insn, FILE *file, int optimize_p ATTRIBUTE_UNUSED,
 	  break;
 
 	case NOTE_INSN_SWITCH_TEXT_SECTIONS:
+	  maybe_output_next_view (seen);
+
 	  in_cold_section_p = !in_cold_section_p;
 
 	  if (in_cold_section_p)
@@ -2301,6 +2410,8 @@ final_scan_insn (rtx_insn *insn, FILE *file, int optimize_p ATTRIBUTE_UNUSED,
 	  break;
 
 	case NOTE_INSN_BLOCK_END:
+	  maybe_output_next_view (seen);
+
 	  if (debug_info_level == DINFO_LEVEL_NORMAL
 	      || debug_info_level == DINFO_LEVEL_VERBOSE
 	      || write_symbols == DWARF2_DEBUG
@@ -2357,7 +2468,10 @@ final_scan_insn (rtx_insn *insn, FILE *file, int optimize_p ATTRIBUTE_UNUSED,
 	case NOTE_INSN_VAR_LOCATION:
 	case NOTE_INSN_CALL_ARG_LOCATION:
 	  if (!DECL_IGNORED_P (current_function_decl))
-	    debug_hooks->var_location (insn);
+	    {
+	      debug_hooks->var_location (insn);
+	      set_next_view_needed (seen);
+	    }
 	  break;
 
 	case NOTE_INSN_BEGIN_STMT:
@@ -2368,6 +2482,7 @@ final_scan_insn (rtx_insn *insn, FILE *file, int optimize_p ATTRIBUTE_UNUSED,
 	      (*debug_hooks->source_line) (last_linenum, last_columnnum,
 					   last_filename, last_discriminator,
 					   true);
+	      clear_next_view_needed (seen);
 	    }
 	  break;
 
@@ -2563,6 +2678,10 @@ final_scan_insn (rtx_insn *insn, FILE *file, int optimize_p ATTRIBUTE_UNUSED,
 
 	    switch_to_section (current_function_section ());
 
+	    if (debug_variable_location_views
+		&& !DECL_IGNORED_P (current_function_decl))
+	      debug_hooks->var_location (insn);
+
 	    break;
 	  }
 	/* Output this line note if it is the first or the last line
@@ -2575,7 +2694,12 @@ final_scan_insn (rtx_insn *insn, FILE *file, int optimize_p ATTRIBUTE_UNUSED,
 	    (*debug_hooks->source_line) (last_linenum, last_columnnum,
 					 last_filename, last_discriminator,
 					 is_stmt);
+	    clear_next_view_needed (seen);
 	  }
+	else
+	  maybe_output_next_view (seen);
+
+	gcc_checking_assert (!DEBUG_INSN_P (insn));
 
 	if (GET_CODE (body) == PARALLEL
 	    && GET_CODE (XVECEXP (body, 0, 0)) == ASM_INPUT)
@@ -3042,7 +3166,8 @@ final_scan_insn (rtx_insn *insn, FILE *file, int optimize_p ATTRIBUTE_UNUSED,
 	/* Let the debug info back-end know about this call.  We do this only
 	   after the instruction has been emitted because labels that may be
 	   created to reference the call instruction must appear after it.  */
-	if (call_insn != NULL && !DECL_IGNORED_P (current_function_decl))
+	if ((debug_variable_location_views || call_insn != NULL)
+	    && !DECL_IGNORED_P (current_function_decl))
 	  debug_hooks->var_location (insn);
 
 	current_output_insn = debug_insn = 0;
@@ -4481,8 +4606,10 @@ rest_of_handle_final (void)
     delete_vta_debug_insns (false);
 
   assemble_start_function (current_function_decl, fnname);
-  final_start_function (get_insns (), asm_out_file, optimize);
-  final (get_insns (), asm_out_file, optimize);
+  rtx_insn *first = get_insns ();
+  int seen = 0;
+  final_start_function_1 (&first, asm_out_file, &seen, optimize);
+  final_1 (first, asm_out_file, seen, optimize);
   if (flag_ipa_ra
       && !lookup_attribute ("noipa", DECL_ATTRIBUTES (current_function_decl)))
     collect_fn_hard_reg_usage ();

gcc/toplev.c

@@ -1558,6 +1558,22 @@ process_options (void)
 	     || write_symbols == VMS_AND_DWARF2_DEBUG)
 	 && !(flag_selective_scheduling || flag_selective_scheduling2));
 
+  if (debug_variable_location_views == AUTODETECT_VALUE)
+    {
+      debug_variable_location_views = flag_var_tracking
+	&& debug_info_level >= DINFO_LEVEL_NORMAL
+	&& (write_symbols == DWARF2_DEBUG
+	    || write_symbols == VMS_AND_DWARF2_DEBUG)
+	&& !dwarf_strict;
+    }
+  else if (debug_variable_location_views == -1 && dwarf_version != 5)
+    {
+      warning_at (UNKNOWN_LOCATION, 0,
+		  "without -gdwarf-5, -gvariable-location-views=incompat5 "
+		  "is equivalent to -gvariable-location-views");
+      debug_variable_location_views = 1;
+    }
+
   if (flag_tree_cselim == AUTODETECT_VALUE)
     {
       if (HAVE_conditional_move)

include/ChangeLog

+2018-02-09  Alexandre Oliva <aoliva@redhat.com>
+
+	* dwarf2.def (DW_AT_GNU_locviews): New.
+	* dwarf2.h (enum dwarf_location_list_entry_type): Add
+	DW_LLE_GNU_view_pair.
+	(DW_LLE_view_pair): Define.
+
 2018-01-03  Jakub Jelinek  <jakub@redhat.com>
 
 	Update copyright years.

include/dwarf2.def

@@ -443,6 +443,7 @@ DW_AT (DW_AT_GNU_pubtypes, 0x2135)
 /* Attribute for discriminator.
    See http://gcc.gnu.org/wiki/Discriminator  */
 DW_AT (DW_AT_GNU_discriminator, 0x2136)
+DW_AT (DW_AT_GNU_locviews, 0x2137)
 /* VMS extensions.  */
 DW_AT (DW_AT_VMS_rtnbeg_pd_address, 0x2201)
 /* GNAT extensions.  */

include/dwarf2.h

@@ -298,6 +298,14 @@ enum dwarf_location_list_entry_type
     DW_LLE_start_end = 0x07,
     DW_LLE_start_length = 0x08,
 
+    /* <http://lists.dwarfstd.org/private.cgi/dwarf-discuss-dwarfstd.org/2017-April/004347.html>
+       has the proposal for now; only available to list members.
+
+       A (possibly updated) copy of the proposal is available at
+       <http://people.redhat.com/aoliva/papers/sfn/dwarf6-sfn-lvu.txt>.  */
+    DW_LLE_GNU_view_pair = 0x09,
+#define DW_LLE_view_pair DW_LLE_GNU_view_pair
+
     /* Former extension for Fission.
        See http://gcc.gnu.org/wiki/DebugFission.  */
     DW_LLE_GNU_end_of_list_entry = 0x00,