Replace exact_log2(x & -x) in favor of more direct computation.

	* toplev.h (ctz_hwi, clz_hwi, ffs_hwi): New.
	(floor_log2): Use clz_hwi.
	(exact_log2): Use ctz_hwi.
	* toplev.c (ctz_hwi, clz_hwi, ffs_hwi): New.
	* builtins.c (fold_builtin_bitop): Use them.
	* simplify-rtx.c (simplify_const_unary_operation): Likewise.
	* combine.c (get_pos_from_mask): Use ctz_hwi.
	* double-int.c (double_int_ctz): Likewise.
	* explow.c (force_reg): Likewise.
	* tree.h (SET_DECL_OFFSET_ALIGN): Use ffs_hwi.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@162920 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 29 insertions, 3 deletions

diff --git a/gcc/toplev.c b/gcc/toplev.c
index 3836d0c50cf..ff824662a22 100644
--- a/gcc/toplev.c
+++ b/gcc/toplev.c
@@ -484,9 +484,9 @@ set_random_seed (const char *val)
 
 #if GCC_VERSION < 3004
 
-/* The functions floor_log2 and exact_log2 are defined as inline
-   functions in toplev.h if GCC_VERSION >= 3004.  The definitions here
-   are used for older versions of gcc.  */
+/* The functions clz_hwi, ctz_hwi, ffs_hwi, floor_log2 and exact_log2
+   are defined as inline functions in toplev.h if GCC_VERSION >= 3004.
+   The definitions here are used for older versions of gcc.  */
 
 /* Given X, an unsigned number, return the largest int Y such that 2**Y <= X.
    If X is 0, return -1.  */
@@ -530,6 +530,32 @@ exact_log2 (unsigned HOST_WIDE_INT x)
   return floor_log2 (x);
 }
 
+/* Given X, an unsigned number, return the number of least significant bits
+   that are zero.  When X == 0, the result is the word size.  */
+
+int
+ctz_hwi (unsigned HOST_WIDE_INT x)
+{
+  return x ? floor_log2 (x & -x) : HOST_BITS_PER_WIDE_INT;
+}
+
+/* Similarly for most significant bits.  */
+
+int
+clz_hwi (unsigned HOST_WIDE_INT x)
+{
+  return HOST_BITS_PER_WIDE_INT - 1 - floor_log2(x);
+}
+
+/* Similar to ctz_hwi, except that the least significant bit is numbered
+   starting from 1, and X == 0 yields 0.  */
+
+int
+ffs_hwi (unsigned HOST_WIDE_INT x)
+{
+  return 1 + floor_log2 (x & -x);
+}
+
 #endif /* GCC_VERSION < 3004 */
 
 /* Handler for fatal signals, such as SIGSEGV.  These are transformed