[gcc r12-2735] Fix debug info for ignored decls at start of assembly

[Bernd Edlinger <edlinger@gcc.gnu.org>]

https://gcc.gnu.org/g:96c82a16b2076891a9974d0f0e96a0b85fbc2df4

commit r12-2735-g96c82a16b2076891a9974d0f0e96a0b85fbc2df4
Author: Bernd Edlinger <bernd.edlinger@hotmail.de>
Date:   Sat Jul 24 12:53:39 2021 +0200

    Fix debug info for ignored decls at start of assembly
    
    Ignored functions decls that are compiled at the start of
    the assembly have bogus line numbers until the first .file
    directive, as reported in PR101575.
    
    The corresponding binutils bug report is
    https://sourceware.org/bugzilla/show_bug.cgi?id=28149
    
    The work around for this issue is to emit a dummy .file
    directive before the first function is compiled, unless
    another .file directive was already emitted previously.
    
    2021-08-04  Bernd Edlinger  <bernd.edlinger@hotmail.de>
    
            PR ada/101575
            * dwarf2out.c (dwarf2out_assembly_start): Emit a dummy
            .file statement when needed.

Diff:
---
 gcc/dwarf2out.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index 884f1e191c6..b91a9b5abaa 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -29389,7 +29389,18 @@ dwarf2out_assembly_start (void)
       output_quoted_string (asm_out_file, remap_debug_filename (filename0));
       fputc ('\n', asm_out_file);
     }
+  else
 #endif
+  /* Work around for PR101575: output a dummy .file directive.  */
+  if (!last_emitted_file && dwarf_debuginfo_p ()
+      && debug_info_level >= DINFO_LEVEL_TERSE)
+    {
+      const char *filename0 = get_AT_string (comp_unit_die (), DW_AT_name);
+
+      if (filename0 == NULL)
+	filename0 = "<dummy>";
+      maybe_emit_file (lookup_filename (filename0));
+    }
 }
 
 /* A helper function for dwarf2out_finish called through