Reduce memory waste due to non-power-of-2 allocs

This patch basically arranges for the allocation size of line_map
buffers to be as close as possible to a power of two.  This
*significantly* decreases peak memory consumption as (macro) maps are
numerous and stay live during all the compilation.

The patch adds a new ggc_round_alloc_size interface to the ggc
allocator.  In each of the two main allocator implementations ('page'
and 'zone') the function has been extracted from the main allocation
function code and returns the actual size of the allocated memory
region, thus giving a chance to the caller to maximize the amount of
memory it actually uses from the allocated memory region.  In the
'none' allocator implementation (that uses xmalloc) the
ggc_round_alloc_size just returns the requested allocation size.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@180086 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 8 insertions, 0 deletions

diff --git a/libcpp/include/line-map.h b/libcpp/include/line-map.h
index 572e330a1bd..1e2a148e17b 100644
--- a/libcpp/include/line-map.h
+++ b/libcpp/include/line-map.h
@@ -53,6 +53,10 @@ typedef unsigned int source_location;
 /* Memory allocation function typedef.  Works like xrealloc.  */
 typedef void *(*line_map_realloc) (void *, size_t);
 
+/* Memory allocator function that returns the actual allocated size,
+   for a given requested allocation.  */
+typedef size_t (*line_map_round_alloc_size_func) (size_t);
+
 /* An ordinary line map encodes physical source locations. Those
    physical source locations are called "spelling locations".
    
@@ -281,6 +285,10 @@ struct GTY(()) line_maps {
   /* If non-null, the allocator to use when resizing 'maps'.  If null,
      xrealloc is used.  */
   line_map_realloc reallocator;
+
+  /* The allocators' function used to know the actual size it
+     allocated, for a certain allocation size requested.  */
+  line_map_round_alloc_size_func round_alloc_size;
 };
 
 /* Returns the pointer to the memory region where information about