ickle at kemper.freedesktop.org
Tue Oct 14 00:22:19 PDT 2008
src/cairo-compiler-private.h | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date: Tue Oct 14 08:17:23 2008 +0100
Add documentation for function attributes 'pure' and 'const'.
Carl suggested that cairo_pure and cairo_const are pretty opaque, even to
the developer who added them, so it is extremely important that they have
a good description so that they are used correctly and perhaps ported to
diff --git a/src/cairo-compiler-private.h b/src/cairo-compiler-private.h
index 9e2b4f6..5195583 100644
@@ -111,6 +111,26 @@
# define CAIRO_FUNCTION_ALIAS(old, new)
+ * Cairo uses the following function attributes in order to improve the
+ * generated code (effectively by manual inter-procedural analysis).
+ * cairo_pure: The function is only allowed to read from its arguments
+ * and global memory (i.e. following a pointer argument or
+ * accessing a shared variable). The return value should
+ * only depend on its arguments, and for an identical set of
+ * arguments should return the same value.
+ * cairo_cont: The function is only allowed to read from its arguments.
+ * It is not allowed to access global memory. The return
+ * value should only depend its arguments, and for an identical
+ * set of arguments should return the same value. This is
+ * currently the most strict function attribute.
+ * Both these function attributes allow gcc to perform CSE and
+ * constant-folding, with cairo_const also guaranteeing that pointer contents
+ * do not change across the function call.
#if __GNUC__ >= 3
#define cairo_pure __attribute__((pure))
#define cairo_const __attribute__((const))
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