[Bug debug/50983] New: [4.7 Regression] incorrect DW_LNS_negate_stmt

[ravitillo at lbl dot gov]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50983

             Bug #: 50983
           Summary: [4.7 Regression] incorrect DW_LNS_negate_stmt
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ravitillo@lbl.gov
                CC: jason@redhat.com


An incorrect DW_LNS_negate_stmt doesn't allow to set breakpoints in some cases,
e.g. given

struct Base {
  Base(bool foo){
    static bool bar;
    if (foo) bar = false; else bar = true;}
};

void fun()
{
  return;
}

int main(int argc, char *argv[])
{
  Base *b = new Base(true);
  fun();
  return 0;
}

and compiling with -g, is_stmt is set to 0 after the end of the first sequence:

  readelf --debug-dump=rawline ./a.out
  ...
  Special opcode 103: advance Address by 7 to 0x40058d and Line by 0 to 4
  Advance PC by 2 to 0x40058f
  Extended opcode 1: End of Sequence

  Set is_stmt to 0
  Extended opcode 2: set Address to 0x400524
  Special opcode 12: advance Address by 0 to 0x400524 and Line by 7 to 8
  ...

making it impossible to set a breakpoint on line 9 for instance. The proposed
fix:


gcc/Changelog:
2011-11-03 Roberto Agostino Vitillo <ravitillo@lbl.gov>
    * dwarf2out.c (set_cur_line_info_table): Restore the last is_stmt value in
the current line table.

Index: gcc/gcc/dwarf2out.c
===================================================================
--- gcc/gcc/dwarf2out.c    (revision 180817)
+++ gcc/gcc/dwarf2out.c    (working copy)
@@ -20363,6 +20363,9 @@
       VEC_safe_push (dw_line_info_table_p, gc, separate_line_info, table);
     }

+  if (DWARF2_ASM_LINE_DEBUG_INFO)
+    table->is_stmt = cur_line_info_table ? cur_line_info_table->is_stmt
+                                         : DWARF_LINE_DEFAULT_IS_STMT_START;
   cur_line_info_table = table;
 }



Tested on x86_64-linux.
r