Size input line cache based on file size

While the input line cache size now tunable it's better if the compiler
auto tunes it. Otherwise large files needing random file access will
still have to search many lines to find the right lines.

Add support for allocating one line anchor per hundred input lines.
This means an overhead of ~235k per 1M input lines on 64bit, which
seems reasonable.

gcc/ChangeLog:

	PR preprocessor/118168
	* input.cc (file_cache_slot::get_next_line): Implement
	dynamic sizing of m_line_record based on input length.
	* params.opt: (param_file_cache_lines): Set to 0 to size
	dynamically.

Author: Andi Kleen

gcc/input.cc

@@ -189,7 +189,7 @@ class file_cache_slot
 
 };
 
-size_t file_cache_slot::line_record_size = 100;
+size_t file_cache_slot::line_record_size = 0;
 
 /* Tune file_cache.  */
 void
@@ -856,8 +856,13 @@ file_cache_slot::get_next_line (char **line, ssize_t *line_len)
       size_t delta = rlen >= 1 ?
 	m_line_num - m_line_record[rlen - 1].line_num : 1;
 
+      size_t max_size = line_record_size;
+      /* One anchor per hundred input lines.  */
+      if (max_size == 0)
+	max_size = m_line_num / 100;
+
       /* If we're too far beyond drop half of the lines to rebalance.  */
-      if (rlen == line_record_size && delta >= spacing*2)
+      if (rlen == max_size && delta >= spacing*2)
 	{
 	  size_t j = 0;
 	  for (size_t i = 1; i < rlen; i += 2)
@@ -867,7 +872,7 @@ file_cache_slot::get_next_line (char **line, ssize_t *line_len)
 	  spacing *= 2;
 	}
 
-      if (rlen < line_record_size && delta >= spacing)
+      if (rlen < max_size && delta >= spacing)
 	m_line_record.safe_push
 	  (file_cache_slot::line_info (m_line_num,
 				       m_line_start_idx,

gcc/params.opt

@@ -136,10 +136,10 @@ Maximal estimated growth of function body caused by early inlining of single cal
 
 -param=file-cache-files=
 Common Joined UInteger Var(param_file_cache_files) Init(16) Param
-Max number of files in the file cache.
+Max number of files in the file cache. When 0 this is automatically sized.
 
 -param=file-cache-lines=
-Common Joined UInteger Var(param_file_cache_lines) Init(100) Param
+Common Joined UInteger Var(param_file_cache_lines) Init(0) Param
 Max number of lines to index into file cache.
 
 -param=fsm-scale-path-stmts=