[pph] cache replace next insert by

[pph] cache replace next insert by

[Gabriel Charette]

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Hey Diego,

as we just talked over the phone, here is the diff I had sitting in my
stash to ask the pph cache to replace the next cache insert by the
given pointer (while still reading what's in the stream).

To use it simply call pph_cache_replace_next_by(stream, your_new_pointer)
and immediately after call pph_in_(whatever you want to read in and
immediately replace the cache pointer value for).

Cheers,
Gab

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diff --git a/gcc/cp/pph-streamer-in.c b/gcc/cp/pph-streamer-in.c
index 0bab93b..aab82a1 100644
--- a/gcc/cp/pph-streamer-in.c
+++ b/gcc/cp/pph-streamer-in.c
@@ -214,6 +214,10 @@ pph_in_start_record (pph_stream *stream, unsigned *cache_ix)
       *cache_ix = -1;
     }
 
+  /* If we just requested a replacement on next insert, the upcoming
+     record better be a new record.  */
+  gcc_assert (!stream->cache.replace_next_by || marker == PPH_RECORD_START);
+
   return marker;
 }
 
@@ -1181,6 +1185,7 @@ pph_in_scope_chain (pph_stream *stream)
 {
   struct cp_binding_level *pph_bindings;
 
+  pph_cache_replace_next_by (stream, scope_chain->bindings);
   pph_bindings = pph_in_binding_level (stream);
 
   /* Merge the bindings obtained from STREAM in the global namespace.  */
diff --git a/gcc/cp/pph-streamer.c b/gcc/cp/pph-streamer.c
index b7ad486..4bc43cb 100644
--- a/gcc/cp/pph-streamer.c
+++ b/gcc/cp/pph-streamer.c
@@ -140,6 +140,7 @@ pph_stream_open (const char *name, const char *mode)
 	pph_init_read (stream);
       stream->cache.v = NULL;
       stream->cache.m = pointer_map_create ();
+      stream->cache.replace_next_by = NULL;
     }
 
   return stream;
@@ -340,13 +341,21 @@ pph_trace_bitpack (pph_stream *stream, struct bitpack_d *bp)
 
 
 /* Insert DATA in STREAM's pickle cache at slot IX.  If DATA already
-   existed in the cache, IX must be the same as the previous entry.  */
+   existed in the cache, IX must be the same as the previous entry.
+   If replace_next_by is set in the cache, discard DATA and use that
+   instead.  */
 
 void
 pph_cache_insert_at (pph_stream *stream, void *data, unsigned ix)
 {
   void **map_slot;
 
+    if (stream->cache.replace_next_by)
+      {
+	data = stream->cache.replace_next_by;
+	stream->cache.replace_next_by = NULL;
+      }
+
   map_slot = pointer_map_insert (stream->cache.m, data);
   if (*map_slot)
     {
diff --git a/gcc/cp/pph-streamer.h b/gcc/cp/pph-streamer.h
index 8d0c024..8ab098d 100644
--- a/gcc/cp/pph-streamer.h
+++ b/gcc/cp/pph-streamer.h
@@ -77,6 +77,12 @@ typedef struct pph_pickle_cache {
 
   /* Map between slots in the array and pointers.  */
   struct pointer_map_t *m;
+
+  /* On the next call to pph_cache_insert_at, put this pointer in the cache
+     instead of the one passed as a parameter. This is used on read to redirect
+     pointers to global structure that already exist in the reader.
+     Regular behavior is maintained if this is NULL.  */
+  void *replace_next_by;
 } pph_pickle_cache;
 
 
@@ -403,4 +409,13 @@ pph_in_bitpack (pph_stream *stream)
   return bp;
 }
 
+
+/* Replace the next cache insert in STREAM by NEW_P.  */
+
+static inline void
+pph_cache_replace_next_by (pph_stream *stream, void *new_p)
+{
+  stream->cache.replace_next_by = new_p;
+}
+
 #endif  /* GCC_CP_PPH_STREAMER_H  */