output: cache the mapped file names

Don't repeatedly call malloc/free for each call to map_file_name.

* bootstrap.conf: We need hash-map.
* src/files.h, src/files.c (map_file_name): The caller must not free
the result.
Adjust callers.
(mapped_dir_prefix, spec_mapped_header_file): Remove.
* src/files.c
(map_file_name): Rename as...
(map_file_name_alloc): this.
(mapped_files, map_file_name, string_equals, string_hash, string_free):
New.

src/files.c

@@ -26,7 +26,9 @@
 #include <error.h>
 #include <get-errno.h>
 #include <gl_array_list.h>
+#include <gl_hash_map.h>
 #include <gl_xlist.h>
+#include <gl_xmap.h>
 #include <quote.h>
 #include <quotearg.h>
 #include <relocatable.h> /* relocate2 */
@@ -58,7 +60,6 @@ char *spec_graph_file = NULL;    /* for -g. */
 char *spec_html_file = NULL;     /* for --html. */
 char *spec_xml_file = NULL;      /* for -x. */
 char *spec_header_file = NULL;   /* for --header. */
-char *spec_mapped_header_file = NULL;
 char *parser_file_name;
 
 /* All computed output file names.  */
@@ -95,7 +96,6 @@ uniqstr grammar_file = NULL;
 char *all_but_ext;
 static char *all_but_tab_ext;
 char *dir_prefix;
-char *mapped_dir_prefix;
 
 /* C source file extension (the parser source).  */
 static char *src_extension = NULL;
@@ -109,6 +109,10 @@ struct prefix_map
 };
 
 static gl_list_t prefix_maps = NULL;
+
+/* Map file names to prefix-mapped file names. */
+static gl_map_t mapped_files = NULL;
+
 
 /*-----------------------------------------------------------------.
 | Return a newly allocated string composed of the concatenation of |
@@ -172,29 +176,25 @@ xfdopen (int fd, char const *mode)
   return res;
 }
 
-/*  Given an input file path, returns a dynamically allocated string that
-    contains the path with the file prefix mapping rules applied, or NULL if
-    the input was NULL. */
-char *
-map_file_name (char const *filename)
+/* The mapped name of FILENAME, allocated, if there are prefix maps.
+   Otherwise NULL.  */
+static char *
+map_file_name_alloc (char const *filename)
 {
-  if (!filename)
-    return NULL;
-
   struct prefix_map const *p = NULL;
-  if (prefix_maps)
-    {
-      void const *ptr;
-      gl_list_iterator_t iter = gl_list_iterator (prefix_maps);
-      while (gl_list_iterator_next (&iter, &ptr, NULL))
-        {
-          p = ptr;
-          if (strncmp (p->oldprefix, filename, strlen (p->oldprefix)) == 0)
-            break;
-          p = NULL;
-        }
-      gl_list_iterator_free (&iter);
-    }
+  assert (prefix_maps);
+  {
+    void const *ptr;
+    gl_list_iterator_t iter = gl_list_iterator (prefix_maps);
+    while (gl_list_iterator_next (&iter, &ptr, NULL))
+      {
+        p = ptr;
+        if (strncmp (p->oldprefix, filename, strlen (p->oldprefix)) == 0)
+          break;
+        p = NULL;
+      }
+    gl_list_iterator_free (&iter);
+  }
 
   if (!p)
     return xstrdup (filename);
@@ -209,6 +209,56 @@ map_file_name (char const *filename)
   return res;
 }
 
+static bool
+string_equals (const void *x1, const void *x2)
+{
+  const char *s1 = x1;
+  const char *s2 = x2;
+  return STREQ (s1, s2);
+}
+
+/* A hash function for NUL-terminated char* strings using
+   the method described by Bruno Haible.
+   See https://www.haible.de/bruno/hashfunc.html.  */
+static size_t
+string_hash (const void *x)
+{
+#define SIZE_BITS (sizeof (size_t) * CHAR_BIT)
+
+  const char *s = x;
+  size_t h = 0;
+
+  for (; *s; s++)
+    h = *s + ((h << 9) | (h >> (SIZE_BITS - 9)));
+
+  return h;
+}
+
+static void
+string_free (const void *p)
+{
+  free ((void*) p);
+}
+
+const char *
+map_file_name (char const *filename)
+{
+  if (!filename || !prefix_maps)
+    return filename;
+  if (!mapped_files)
+    mapped_files
+      = gl_map_nx_create_empty (GL_HASH_MAP,
+                                string_equals, string_hash,
+                                string_free, string_free);
+  const void *res = gl_map_get (mapped_files, filename);
+  if (!res)
+    {
+      res = map_file_name_alloc (filename);
+      gl_map_put (mapped_files, xstrdup (filename), res);
+    }
+  return res;
+}
+
 static void
 prefix_map_free (struct prefix_map *p)
 {
@@ -445,9 +495,6 @@ compute_output_file_names (void)
       output_file_name_check (&spec_verbose_file, false);
     }
 
-  spec_mapped_header_file = map_file_name (spec_header_file);
-  mapped_dir_prefix = map_file_name (dir_prefix);
-
   free (all_but_tab_ext);
   free (src_extension);
   free (header_extension);
@@ -535,10 +582,8 @@ output_file_names_free (void)
   free (spec_html_file);
   free (spec_xml_file);
   free (spec_header_file);
-  free (spec_mapped_header_file);
   free (parser_file_name);
   free (dir_prefix);
-  free (mapped_dir_prefix);
   for (int i = 0; i < generated_files_size; i++)
     free (generated_files[i].name);
   free (generated_files);
@@ -546,4 +591,6 @@ output_file_names_free (void)
 
   if (prefix_maps)
     gl_list_free (prefix_maps);
+  if (mapped_files)
+    gl_map_free (mapped_files);
 }