[Pixman] [PATCH] implementation: add PIXMAN_DISABLE=wholeops

[Pekka Paalanen]

From: Pekka Paalanen <pekka.paalanen at collabora.co.uk>

Add a new option to PIXMAN_DISABLE: "wholeops". This option disables all
whole-operation fast paths regardless of implementation level, except
the general path (general_composite_rect).

The purpose is to add a debug option that allows us to test optimized
iterator paths specifically. With this, it is possible to see if:
- fast paths mask bugs in iterators
- compare fast paths with iterator paths for performance

The effect was tested on x86_64 by running:
$ PIXMAN_DISABLE='' ./test/lowlevel-blt-bench over_8888_8888
$ PIXMAN_DISABLE='wholeops' ./test/lowlevel-blt-bench over_8888_8888

In the first case time is spent in sse2_composite_over_8888_8888(), and
in the latter in sse2_combine_over_u().

Signed-off-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
---
 pixman/pixman-implementation.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/pixman/pixman-implementation.c b/pixman/pixman-implementation.c
index 5884054..2c7de4c 100644
--- a/pixman/pixman-implementation.c
+++ b/pixman/pixman-implementation.c
@@ -380,6 +380,11 @@ _pixman_disabled (const char *name)
     return FALSE;
 }
 
+static const pixman_fast_path_t empty_fast_path[] =
+{
+    { PIXMAN_OP_NONE }
+};
+
 pixman_implementation_t *
 _pixman_choose_implementation (void)
 {
@@ -397,5 +402,16 @@ _pixman_choose_implementation (void)
 
     imp = _pixman_implementation_create_noop (imp);
 
+    if (_pixman_disabled ("wholeops"))
+    {
+        pixman_implementation_t *cur;
+
+        /* Disable all whole-operation paths except the general one,
+         * so that optimized iterators are used as much as possible.
+         */
+        for (cur = imp; cur->fallback; cur = cur->fallback)
+            cur->fast_paths = empty_fast_path;
+    }
+
     return imp;
 }
-- 
2.4.6