The existing ltu_p fast path can handle any pairs of single-HWI inputs,
even for precision > HOST_BITS_PER_WIDE_INT. In that case both xl and
yl are implicitly sign-extended to the larger precision, but with the
extended values still being compared as unsigned. The extension doesn't
change the result in that case.
When compiling a recent fold-const.ii, this reduces the number of
ltu_p_large calls from 23849 to 697.
Tested on x86_64-linux-gnu. OK to install?
Thanks,
Richard
Index: gcc/alias.c
===================================================================
--- gcc/alias.c 2013-11-20 12:12:49.393055063 +0000
+++ gcc/alias.c 2013-11-28 12:24:23.307549245 +0000
@@ -342,7 +342,7 @@ ao_ref_from_mem (ao_ref *ref, const_rtx
|| (DECL_P (ref->base)
&& (DECL_SIZE (ref->base) == NULL_TREE
|| TREE_CODE (DECL_SIZE (ref->base)) != INTEGER_CST
- || wi::ltu_p (DECL_SIZE (ref->base),
+ || wi::ltu_p (wi::to_offset (DECL_SIZE (ref->base)),
ref->offset + ref->size)))))
return false;
Index: gcc/wide-int.h
===================================================================
--- gcc/wide-int.h 2013-11-28 11:44:39.041731636 +0000
+++ gcc/wide-int.h 2013-11-28 12:48:36.200764215 +0000
@@ -1740,13 +1740,15 @@ wi::ltu_p (const T1 &x, const T2 &y)
unsigned int precision = get_binary_precision (x, y);
WIDE_INT_REF_FOR (T1) xi (x, precision);
WIDE_INT_REF_FOR (T2) yi (y, precision);
- /* Optimize comparisons with constants and with sub-HWI unsigned
- integers. */
+ /* Optimize comparisons with constants. */
if (STATIC_CONSTANT_P (yi.len == 1 && yi.val[0] >= 0))
return xi.len == 1 && xi.to_uhwi () < (unsigned HOST_WIDE_INT) yi.val[0];
if (STATIC_CONSTANT_P (xi.len == 1 && xi.val[0] >= 0))
return yi.len != 1 || yi.to_uhwi () > (unsigned HOST_WIDE_INT) xi.val[0];
- if (precision <= HOST_BITS_PER_WIDE_INT)
+ /* Optimize the case of two HWIs. The HWIs are implicitly sign-extended
+ for precisions greater than HOST_BITS_WIDE_INT, but sign-extending both
+ values does not change the result. */
+ if (xi.len + yi.len == 2)
{
unsigned HOST_WIDE_INT xl = xi.to_uhwi ();
unsigned HOST_WIDE_INT yl = yi.to_uhwi ();
