gas/Dwarf: properly skip zero-size functions

PR gas/29451

While out_debug_abbrev() properly skips such functions, out_debug_info()
mistakenly didn't. It needs to calculate the high_pc expression ahead of
time, in order to skip emitting any data for the function if the value
is zero.

The one case which would still leave a zero-size entry is when
symbol_get_obj(symp)->size ends up evaluating to zero. I hope we can
expect that to not be the case, otherwise we'd need to have a way to
post-process .debug_info contents between resolving expressions and
actually writing the data out to the file. Even then it wouldn't be
entirely obvious in which way to alter the data.

gas/dwarf2dbg.c

@@ -2882,6 +2882,7 @@ out_debug_info (segT info_seg, segT abbrev_seg, segT line_seg, segT str_seg,
 	{
 	  const char *name;
 	  size_t len;
+	  expressionS size = { .X_op = O_constant };
 
 	  /* Skip warning constructs (see above).  */
 	  if (symbol_get_bfdsym (symp)->flags & BSF_WARNING)
@@ -2895,6 +2896,18 @@ out_debug_info (segT info_seg, segT abbrev_seg, segT line_seg, segT str_seg,
 	  if (!S_IS_DEFINED (symp) || !S_IS_FUNCTION (symp))
 	    continue;
 
+#if defined (OBJ_ELF) /* || defined (OBJ_MAYBE_ELF) */
+	  size.X_add_number = S_GET_SIZE (symp);
+	  if (size.X_add_number == 0 && IS_ELF
+	      && symbol_get_obj (symp)->size != NULL)
+	    {
+	      size.X_op = O_add;
+	      size.X_op_symbol = make_expr_symbol (symbol_get_obj (symp)->size);
+	    }
+#endif
+	  if (size.X_op == O_constant && size.X_add_number == 0)
+	    continue;
+
 	  subseg_set (str_seg, 0);
 	  name_sym = symbol_temp_new_now_octets ();
 	  name = S_GET_NAME (symp);
@@ -2920,29 +2933,17 @@ out_debug_info (segT info_seg, segT abbrev_seg, segT line_seg, segT str_seg,
 	  emit_expr (&exp, sizeof_address);
 
 	  /* DW_AT_high_pc */
-	  exp.X_op = O_constant;
-#if defined (OBJ_ELF) /* || defined (OBJ_MAYBE_ELF) */
-	  exp.X_add_number = S_GET_SIZE (symp);
-	  if (exp.X_add_number == 0 && IS_ELF
-	      && symbol_get_obj (symp)->size != NULL)
-	    {
-	      exp.X_op = O_add;
-	      exp.X_op_symbol = make_expr_symbol (symbol_get_obj (symp)->size);
-	    }
-#else
-	  exp.X_add_number = 0;
-#endif
 	  if (DWARF2_VERSION < 4)
 	    {
-	      if (exp.X_op == O_constant)
-		exp.X_op = O_symbol;
-	      exp.X_add_symbol = symp;
-	      emit_expr (&exp, sizeof_address);
+	      if (size.X_op == O_constant)
+		size.X_op = O_symbol;
+	      size.X_add_symbol = symp;
+	      emit_expr (&size, sizeof_address);
 	    }
-	  else if (exp.X_op == O_constant)
-	    out_uleb128 (exp.X_add_number);
+	  else if (size.X_op == O_constant)
+	    out_uleb128 (size.X_add_number);
 	  else
-	    emit_leb128_expr (symbol_get_value_expression (exp.X_op_symbol), 0);
+	    emit_leb128_expr (symbol_get_value_expression (size.X_op_symbol), 0);
 	}
 
       /* End of children.  */