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* [PATCH] Remove unused extern variables from debug (PR debug/86964)
@ 2019-02-19 12:51 Johan Carlsson
  2019-02-21 19:22 ` Jeff Law
  2019-03-25 21:22 ` Jeff Law
  0 siblings, 2 replies; 5+ messages in thread
From: Johan Carlsson @ 2019-02-19 12:51 UTC (permalink / raw)
  To: gcc-patches; +Cc: rguenther

Adding so that the DIEs of unused external variables can be removed from the output when
using -feliminate-unused-debug-symbols.

Tested on x86_64-elf, aarch64-elf, powerpc-eabi, powerpc64-elf and arm-eabi.


2019-02-18  Johan Karlsson <johan.karlsson@enea.com>

	PR debug/86964
	* dwarf2out.c (premark_used_variables): New function.
	(prune_unused_types_walk): Do not mark not premarked external
	variables.
	(prune_unused_types): Call premark_used_variables.

	* gcc.dg/debug/dwarf2/pr86964.c: New testcase.

Index: gcc/dwarf2out.c
===================================================================
--- gcc/dwarf2out.c	(revision 268977)
+++ gcc/dwarf2out.c	(working copy)
@@ -22658,6 +22658,21 @@ premark_types_used_by_global_vars (void)
       ->traverse<void *, premark_types_used_by_global_vars_helper> (NULL);
 }
 
+/* Mark all variables used by the symtab as perennial.  */
+
+static void
+premark_used_variables (void)
+{
+  /* Mark DIEs in the symtab as used.  */
+  varpool_node *var;
+  FOR_EACH_VARIABLE (var)
+    {
+      dw_die_ref die = lookup_decl_die (var->decl);
+      if (die)
+	die->die_perennial_p = 1;
+    }
+}
+
 /* Generate a DW_TAG_call_site DIE in function DECL under SUBR_DIE
    for CA_LOC call arg loc node.  */
 
@@ -29264,6 +29279,19 @@ prune_unused_types_walk (dw_die_ref die)
 
       return;
 
+    case DW_TAG_variable:
+      if (flag_debug_only_used_symbols)
+	{
+	  if (die->die_perennial_p)
+	    break;
+
+	  /* premark_used_variables marks external variables --- don't mark
+	     them here.  */
+	  if (get_AT (die, DW_AT_external))
+	    return;
+	}
+      /* FALLTHROUGH */
+
     default:
       /* Mark everything else.  */
       break;
@@ -29390,6 +29418,10 @@ prune_unused_types (void)
   /* Mark types that are used in global variables.  */
   premark_types_used_by_global_vars ();
 
+  /* Mark variables used in the symtab.  */
+  if (flag_debug_only_used_symbols)
+    premark_used_variables ();
+
   /* Set the mark on nodes that are actually used.  */
   prune_unused_types_walk (comp_unit_die ());
   for (node = limbo_die_list; node; node = node->next)
Index: gcc/testsuite/gcc.dg/debug/dwarf2/pr86964.c
===================================================================
--- gcc/testsuite/gcc.dg/debug/dwarf2/pr86964.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/debug/dwarf2/pr86964.c	(working copy)
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -gdwarf -feliminate-unused-debug-symbols -dA" } */
+
+struct S { int i; };
+extern struct S x;
+int y;
+int main()
+{
+  return y;
+}
+
+/* We should elide the DIEs for x and S but not y.  */
+/* { dg-final { scan-assembler-times "DW_TAG_variable" 2 } } */
+/* { dg-final { scan-assembler-not "DW_TAG_structure_type" } } */

^ permalink raw reply	[flat|nested] 5+ messages in thread
end of thread, other threads:[~2019-03-25 21:19 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-02-19 12:51 [PATCH] Remove unused extern variables from debug (PR debug/86964) Johan Carlsson
2019-02-21 19:22 ` Jeff Law
2019-02-21 19:50   ` Richard Biener
2019-02-21 21:45     ` Jeff Law
2019-03-25 21:22 ` Jeff Law

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