These are really useful hints to the compiler in the absence of link-time
optimization, and I'm going to use them in VC4.
I've made the const attribute be ATTRIBUTE_CONST unlike other function
attributes, because we have other things in the tree #defining CONST for
their own unrelated purposes.
---
configure.ac | 2 ++
src/util/macros.h | 20 ++++++++++++++++++++
2 files changed, 22 insertions(+)
diff --git a/configure.ac b/configure.ac
index bdfd134..38ad398 100644
--- a/configure.ac
+++ b/configure.ac
@@ -210,6 +210,8 @@ AX_GCC_FUNC_ATTRIBUTE([format])
AX_GCC_FUNC_ATTRIBUTE([malloc])
AX_GCC_FUNC_ATTRIBUTE([packed])
AX_GCC_FUNC_ATTRIBUTE([unused])
+AX_GCC_FUNC_ATTRIBUTE([const])
+AX_GCC_FUNC_ATTRIBUTE([pure])
AX_GCC_FUNC_ATTRIBUTE([warn_unused_result])
AM_CONDITIONAL([GEN_ASM_OFFSETS], test "x$GEN_ASM_OFFSETS" = xyes)
diff --git a/src/util/macros.h b/src/util/macros.h
index 66698e7..4d16183 100644
--- a/src/util/macros.h
+++ b/src/util/macros.h
@@ -130,6 +130,26 @@ do { \
#define PACKED
#endif
+/* Attribute pure is used for functions that have no effects other than their
+ * return value. As a result, calls to it can be dead code eliminated.
+ */
+#ifdef HAVE_FUNC_ATTRIBUTE_PURE
+#define PURE __attribute__((__pure__))
+#else
+#define PURE
+#endif
+
+/* Attribute const is used for functions that have no effects other than their
+ * return value, and only rely on the argument values to compute the return
+ * value. As a result, calls to it can be CSEed. Note that using memory
+ * pointed to by the arguments is not allowed for const functions.
+ */
+#ifdef HAVE_FUNC_ATTRIBUTE_CONST
+#define ATTRIBUTE_CONST __attribute__((__const__))
+#else
+#define ATTRIBUTE_CONST
+#endif
+
#ifdef __cplusplus
/**
* Macro function that evaluates to true if T is a trivially
--
2.1.4
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