Patchwork Instance information in DWARF discriminators

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Submitter Thomas Quinot
Date Dec. 5, 2012, 3:14 p.m.
Message ID <20121205151443.GC42540@melamine.cuivre.fr.eu.org>
Download mbox | patch
Permalink /patch/203885/
State New
Headers show

Comments

Thomas Quinot - Dec. 5, 2012, 3:14 p.m.
* Tom Tromey, 2012-11-29 :

> Thomas> Now, an alternative might be to have an array of instance IDs stored at
> Thomas> the struct line_maps level, with the same indices at the set of ordinary
> Thomas> maps, which would be allocated only when flag_debug_instances is used;
> Thomas> when it is not used the cost would then be a single NULL pointer in
> Thomas> struct line_maps. Would that be acceptable?
> 
> I thought there was already a similar approach in place.
> See location_adhoc_data.
> The proliferation of ways to do this is mildly worrying.

Tom,

location_adhoc_data is not really appropriate as it associates data with
a single locus, whereas we need an instance identifier for all loci
covered by a given line map entry.

Attached to this message is an update patch based on an alternative
approach, consisting in maintaining the instance ids in a parallel map
that is allocated only when actually used. In this way, the cost when
not using the option is reduced to a single NULL pointer in struct
line_maps.

This change also attempts to better document the new flag, as pointed
out by Richard, and fixes a few style nits. The LTO streaming part is
still missing.

The updated ChangeLog is:

gcc/
        * common.opt (flag_debug_instances): Define new internal flag.
        * final.c (notice_source_line): If flag_debug_instances is set,
        set discriminator to current instance id.
	* emit-rtl.c (insn_instance): New subprogram, retrieves instance
	identifier from insn.
	* rtl.h (insn_instance): Declare.
	* input.h (LOCATION_INSTANCE): Define.
        * tree-cfg.c (assign_discriminator): If flag_debug_instances is set,
        nothing to do here.

libcpp/
        * include/line_map.h (struct line_maps): Add instance_ids field
	(table for use under flag_debug_instances).
        (expanded_location): Add instance id field.
        (LINEMAPS_INSTANCE_IDS): Define.
	(ORDINARY_MAP_INSTANCE): Define.
        * line-map.c (linemap_expand_location): Set instance field in expanded
        location from same in set.

Patch

Index: gcc/rtl.h
===================================================================
--- gcc/rtl.h	(révision 193884)
+++ gcc/rtl.h	(copie de travail)
@@ -1917,6 +1917,7 @@ 
 /* In emit-rtl.c  */
 extern int insn_line (const_rtx);
 extern const char * insn_file (const_rtx);
+extern int insn_instance (const_rtx);
 extern tree insn_scope (const_rtx);
 extern location_t prologue_location, epilogue_location;
 
Index: gcc/final.c
===================================================================
--- gcc/final.c	(révision 193884)
+++ gcc/final.c	(copie de travail)
@@ -2894,6 +2894,8 @@ 
     {
       filename = insn_file (insn);
       linenum = insn_line (insn);
+      if (flag_debug_instances)
+        discriminator = insn_instance (insn);
     }
 
   if (filename == NULL)
Index: gcc/input.h
===================================================================
--- gcc/input.h	(révision 193884)
+++ gcc/input.h	(copie de travail)
@@ -51,6 +51,7 @@ 
 #define LOCATION_FILE(LOC) ((expand_location (LOC)).file)
 #define LOCATION_LINE(LOC) ((expand_location (LOC)).line)
 #define LOCATION_COLUMN(LOC)((expand_location (LOC)).column)
+#define LOCATION_INSTANCE(LOC) ((expand_location (LOC)).instance)
 #define LOCATION_LOCUS(LOC) \
   ((IS_ADHOC_LOC(LOC)) ? get_location_from_adhoc_loc (line_table, LOC) : (LOC))
 #define LOCATION_BLOCK(LOC) \
Index: gcc/emit-rtl.c
===================================================================
--- gcc/emit-rtl.c	(révision 193884)
+++ gcc/emit-rtl.c	(copie de travail)
@@ -6007,6 +6007,14 @@ 
   return LOCATION_FILE (INSN_LOCATION (insn));
 }
 
+/* Return source instance of the statement that produced this insn.  */
+
+int
+insn_instance (const_rtx insn)
+{
+  return LOCATION_INSTANCE (INSN_LOCATION (insn));
+}
+
 /* Return true if memory model MODEL requires a pre-operation (release-style)
    barrier or a post-operation (acquire-style) barrier.  While not universal,
    this function matches behavior of several targets.  */
Index: gcc/common.opt
===================================================================
--- gcc/common.opt	(révision 193884)
+++ gcc/common.opt	(copie de travail)
@@ -158,6 +158,15 @@ 
 Variable
 int flag_debug_asm
 
+; Language front-ends that support multiple instantiations of a given
+; source template (such as Ada with generics) may enable this flag, and
+; provide instance identifiers in the line map, so that discriminators in
+; DWARF debugging information carry these instance identifiers, allowing
+; external tools to identify which instance a given object instruction comes
+; from.
+Variable
+int flag_debug_instances = 0
+
 ; -dP causes the rtl to be emitted as a comment in assembly.
 Variable
 int flag_dump_rtl_in_asm
Index: gcc/tree-cfg.c
===================================================================
--- gcc/tree-cfg.c	(révision 193884)
+++ gcc/tree-cfg.c	(copie de travail)
@@ -768,7 +768,7 @@ 
 {
   gimple first_in_to_bb, last_in_to_bb;
 
-  if (locus == 0 || bb->discriminator != 0)
+  if (locus == 0 || bb->discriminator != 0 || flag_debug_instances)
     return;
 
   first_in_to_bb = first_non_label_stmt (bb);
Index: libcpp/include/line-map.h
===================================================================
--- libcpp/include/line-map.h	(révision 193884)
+++ libcpp/include/line-map.h	(copie de travail)
@@ -230,6 +230,12 @@ 
 #define ORDINARY_MAP_NUMBER_OF_COLUMN_BITS(MAP) \
   linemap_check_ordinary (MAP)->d.ordinary.column_bits
 
+#define ORDINARY_MAP_INSTANCE(SET,MAP) \
+  (LINEMAPS_INSTANCE_IDS(SET) != NULL ? \
+  LINEMAPS_INSTANCE_IDS(SET)[linemap_check_ordinary (MAP) - \
+                             LINEMAPS_ORDINARY_MAP_AT(SET, 0)] : \
+  0)
+
 #define MACRO_MAP_MACRO(MAP) (MAP)->d.macro.macro
 
 #define MACRO_MAP_NUM_MACRO_TOKENS(MAP) (MAP)->d.macro.n_tokens
@@ -291,6 +297,13 @@ 
 
   struct maps_info info_macro;
 
+  /* For languages that have the notion of instantiating a given template
+     multiple times, different line_maps can be allocated for each instance,
+     which are distinguished by an instance identifier. When
+     flag_debug_instaces is enabled, this table (which has the same indices
+     as the ordinary linemaps in this set) stores these instance ids.  */
+  int * GTY((atomic)) instance_ids;
+
   /* Depth of the include stack, including the current file.  */
   unsigned int depth;
 
@@ -369,6 +382,11 @@ 
 #define LINEMAPS_ORDINARY_MAPS(SET) \
   LINEMAPS_MAPS (SET, false)
 
+/* Returns the vector of instance identifiers associated to ordinary maps in
+   the line table SET.  */
+#define LINEMAPS_INSTANCE_IDS(SET) \
+  (SET)->instance_ids
+
 /* Returns the INDEXth ordinary map.  */
 #define LINEMAPS_ORDINARY_MAP_AT(SET, INDEX)	\
   LINEMAPS_MAP_AT (SET, false, INDEX)
@@ -638,6 +656,9 @@ 
 
   /* In a system header?. */
   bool sysp;
+
+  /* Instance id.  */
+  int instance;
 } expanded_location;
 
 /* This is enum is used by the function linemap_resolve_location
Index: libcpp/line-map.c
===================================================================
--- libcpp/line-map.c	(révision 193884)
+++ libcpp/line-map.c	(copie de travail)
@@ -1395,6 +1395,7 @@ 
       xloc.line = SOURCE_LINE (map, loc);
       xloc.column = SOURCE_COLUMN (map, loc);
       xloc.sysp = LINEMAP_SYSP (map) != 0;
+      xloc.instance = ORDINARY_MAP_INSTANCE (set, map);
     }
 
   return xloc;