[SFN] Introduce -gstatement-frontiers option, enable debug markers

Introduce a command line option to enable statement frontiers, enabled
by default in optimized builds with DWARF2+ debug information.

This patch depends on an earlier patch that completed the
infrastructure for debug markers, and on another patch that turns -g
into a negatable option prefix.

for  gcc/ChangeLog

	* common.opt (gstatement-frontiers): New, setting
	debug_nonbind_markers_p.
	* rtl.h (MAY_HAVE_DEBUG_MARKER_INSNS): Activate.
	* toplev.c (process_options): Autodetect value for debug statement
	frontiers option.
	* tree.h (MAY_HAVE_DEBUG_MARKER_STMTS): Activate.
	* doc/invoke.texi (gstatement-frontiers, gno-statement-frontiers): New.

From-SVN: r255569

gcc/ChangeLog

@@ -1,5 +1,13 @@
 2017-12-12  Alexandre Oliva <aoliva@redhat.com>
 
+	* common.opt (gstatement-frontiers): New, setting
+	debug_nonbind_markers_p.
+	* rtl.h (MAY_HAVE_DEBUG_MARKER_INSNS): Activate.
+	* toplev.c (process_options): Autodetect value for debug statement
+	frontiers option.
+	* tree.h (MAY_HAVE_DEBUG_MARKER_STMTS): Activate.
+	* doc/invoke.texi (gstatement-frontiers, gno-statement-frontiers): New.
+
 	* cfgexpand.c (expand_gimple_basic_block): Handle begin stmt
 	markers.  Integrate source bind into debug stmt expand loop.
 	(pass_expand::execute): Check debug marker limit.  Avoid deep

gcc/common.opt

@@ -2936,6 +2936,10 @@ gstabs+
 Common Driver JoinedOrMissing Negative(gvms)
 Generate debug information in extended STABS format.
 
+gstatement-frontiers
+Common Driver Var(debug_nonbind_markers_p) Init(2)
+Emit progressive recommended breakpoint locations.
+
 gstrict-dwarf
 Common Driver Report Var(dwarf_strict) Init(0)
 Don't emit DWARF additions beyond selected version.

gcc/doc/invoke.texi

@@ -346,6 +346,7 @@ Objective-C and Objective-C++ Dialects}.
 -ggdb  -grecord-gcc-switches  -gno-record-gcc-switches @gol
 -gstabs  -gstabs+  -gstrict-dwarf  -gno-strict-dwarf @gol
 -gcolumn-info  -gno-column-info @gol
+-gstatement-frontiers  -gno-statement-frontiers @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
@@ -7146,6 +7147,17 @@ Emit location column information into DWARF debugging information, rather
 than just file and line.
 This option is enabled by default.
 
+@item -gstatement-frontiers
+@item -gno-statement-frontiers
+@opindex gstatement-frontiers
+@opindex gno-statement-frontiers
+This option causes GCC to create markers in the internal representation
+at the beginning of statements, and to keep them roughly in place
+throughout compilation, using them to guide the output of @code{is_stmt}
+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 -gz@r{[}=@var{type}@r{]}
 @opindex gz
 Produce compressed debug sections in DWARF format, if that is supported.

gcc/rtl.h

@@ -816,7 +816,7 @@ struct GTY(()) rtvec_def {
 #define NONDEBUG_INSN_P(X) (INSN_P (X) && !DEBUG_INSN_P (X))
 
 /* Nonzero if DEBUG_MARKER_INSN_P may possibly hold.  */
-#define MAY_HAVE_DEBUG_MARKER_INSNS 0 /* debug_nonbind_markers_p */
+#define MAY_HAVE_DEBUG_MARKER_INSNS debug_nonbind_markers_p
 /* Nonzero if DEBUG_BIND_INSN_P may possibly hold.  */
 #define MAY_HAVE_DEBUG_BIND_INSNS flag_var_tracking_assignments
 /* Nonzero if DEBUG_INSN_P may possibly hold.  */

gcc/toplev.c

@@ -1536,6 +1536,10 @@ process_options (void)
     warning_at (UNKNOWN_LOCATION, 0,
 		"var-tracking-assignments changes selective scheduling");
 
+  if (debug_nonbind_markers_p == AUTODETECT_VALUE)
+    debug_nonbind_markers_p = optimize && debug_info_level >= DINFO_LEVEL_NORMAL
+      && (write_symbols == DWARF2_DEBUG || write_symbols == VMS_AND_DWARF2_DEBUG);
+
   if (flag_tree_cselim == AUTODETECT_VALUE)
     {
       if (HAVE_conditional_move)

gcc/tree.h

@@ -1124,7 +1124,7 @@ extern void omp_clause_range_check_failed (const_tree, const char *, int,
   ((int)TREE_INT_CST_LOW (VL_EXP_CHECK (NODE)->exp.operands[0]))
 
 /* Nonzero if gimple_debug_nonbind_marker_p() may possibly hold.  */
-#define MAY_HAVE_DEBUG_MARKER_STMTS 0 /* debug_nonbind_markers_p */
+#define MAY_HAVE_DEBUG_MARKER_STMTS debug_nonbind_markers_p
 /* Nonzero if gimple_debug_bind_p() (and thus
    gimple_debug_source_bind_p()) may possibly hold.  */
 #define MAY_HAVE_DEBUG_BIND_STMTS flag_var_tracking_assignments