cpplib speed hack

[Zack Weinberg <zack at rabi dot columbia dot edu>]

cpplib contains two functions, skip_rest_of_line and
copy_rest_of_line, which do what they sound like.  Currently
skip_rest_of_line calls copy_rest_of_line and then throws away the
text that's been copied.  Profiling indicates that more than 75% of
calls to c_r_o_l are either from s_r_o_l or skip_if_group, which also
copies the text only to discard it.

By rewriting s_r_o_l to do the forward scan itself, we get about 5%
performance improvement compiling GNU libc, at the cost of some code
duplication.

(old) 1:44:41 - 5049.70 user, 538.54 system, 88% cpu
(new) 1:39:12 - 4986.01 user, 526.64 system, 92% cpu

I am not sure why system time is reduced.  It is probably unrelated.

This patch is relative to the previous patch for cpplib (line numbering
bugfix) but should apply cleanly-but-offset without it.

zw

1999-04-16 23:14 -0400  Zack Weinberg  <zack@rabi.phys.columbia.edu>

	* cpplib.c (skip_rest_of_line):  Do the forward scan here
	instead of calling copy_rest_of_line.
	(skip_if_group): Call skip_rest_of_line not copy_rest_of_line.

--- cpplib.c.prev	Thu Apr 15 20:51:30 1999
+++ cpplib.c	Fri Apr 16 23:05:12 1999
@@ -476,17 +476,54 @@
     }
 }
 
-/* FIXME: It is almost definitely a performance win to make this do
-   the scan itself.  >75% of calls to copy_r_o_l are from here or
-   skip_if_group, which means the common case is to copy stuff into the
-   token_buffer only to discard it.  */
+/* Read the rest of the current line and discard it. */
+
 void
 skip_rest_of_line (pfile)
      cpp_reader *pfile;
 {
-  long old = CPP_WRITTEN (pfile);
-  copy_rest_of_line (pfile);
-  CPP_SET_WRITTEN (pfile, old);
+  long here = CPP_WRITTEN (pfile);
+  for (;;)
+    {
+      int c = GETC();
+      switch (c)
+	{
+	case '\n':
+	  FORWARD(-1);
+	case EOF:
+	  return;
+
+	case '\r':
+	  if (!CPP_BUFFER (pfile)->has_escapes)
+	      CPP_BUFFER (pfile)->lineno++;
+	  break;
+	  
+	case '\'':
+	case '\"':
+	  parse_string (pfile, c);
+	  CPP_SET_WRITTEN (pfile, here);
+	  break;
+
+	case '/':
+	  if (PEEKC() == '*' && CPP_TRADITIONAL (pfile))
+	    {
+	      CPP_PUTS (pfile, "/**/", 4);
+	      skip_comment (pfile, c);
+	      break;
+	    }
+	  /* else fall through */
+	case '-':
+	  c = skip_comment (pfile, c);
+	  break;
+
+	case '\f':
+	case '\v':
+	  if (CPP_PEDANTIC (pfile))
+	    cpp_pedwarn (pfile, "%s in preprocessing directive",
+			 c == '\f' ? "formfeed" : "vertical tab");
+	  break;
+	}
+    }
 }
 
 /* Handle a possible # directive.
@@ -1877,7 +1859,6 @@
   int c;
   IF_STACK_FRAME *save_if_stack = pfile->if_stack; /* don't pop past here */
   U_CHAR *beg_of_line;
-  long old_written;
 
   if (CPP_OPTIONS (pfile)->output_conditionals)
     {
@@ -1886,8 +1867,6 @@
       output_line_command (pfile, same_file);
     }
 
-  old_written = CPP_WRITTEN (pfile);
-  
   for (;;)
     {
       beg_of_line = CPP_BUFFER (pfile)->cur;
@@ -1917,10 +1896,7 @@
 	  copy_rest_of_line (pfile);
 	}
       else
-	{
-	  copy_rest_of_line (pfile);
-	  CPP_SET_WRITTEN (pfile, old_written);	 /* discard it */
-	}
+	skip_rest_of_line (pfile);
 
       c = GETC();
       if (c == EOF)