Without profiling information, GCC tends to assume "x == 1" and "x + y == 2" are likely false, so this patch adds some __builtin_expects. (system.h has a dummy definition for compilers that don't support __builtin_expect.)
Tested on x86_64-linux-gnu. OK to install? Thanks, Richard Index: gcc/wide-int.h =================================================================== --- gcc/wide-int.h 2013-11-30 09:40:32.710196218 +0000 +++ gcc/wide-int.h 2013-11-30 10:07:06.567433289 +0000 @@ -1675,7 +1675,7 @@ wi::eq_p (const T1 &x, const T2 &y) while (++i != xi.len); return true; } - if (yi.len == 1) + if (__builtin_expect (yi.len == 1, true)) { /* XI is only equal to YI if it too has a single HWI. */ if (xi.len != 1) @@ -1751,7 +1751,7 @@ wi::ltu_p (const T1 &x, const T2 &y) /* 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) + if (__builtin_expect (xi.len + yi.len == 2, true)) { unsigned HOST_WIDE_INT xl = xi.to_uhwi (); unsigned HOST_WIDE_INT yl = yi.to_uhwi (); @@ -1922,7 +1922,7 @@ wi::cmpu (const T1 &x, const T2 &y) /* 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) + if (__builtin_expect (xi.len + yi.len == 2, true)) { unsigned HOST_WIDE_INT xl = xi.to_uhwi (); unsigned HOST_WIDE_INT yl = yi.to_uhwi (); @@ -2128,7 +2128,7 @@ wi::bit_and (const T1 &x, const T2 &y) WIDE_INT_REF_FOR (T1) xi (x, precision); WIDE_INT_REF_FOR (T2) yi (y, precision); bool is_sign_extended = xi.is_sign_extended && yi.is_sign_extended; - if (xi.len + yi.len == 2) + if (__builtin_expect (xi.len + yi.len == 2, true)) { val[0] = xi.ulow () & yi.ulow (); result.set_len (1, is_sign_extended); @@ -2149,7 +2149,7 @@ wi::bit_and_not (const T1 &x, const T2 & WIDE_INT_REF_FOR (T1) xi (x, precision); WIDE_INT_REF_FOR (T2) yi (y, precision); bool is_sign_extended = xi.is_sign_extended && yi.is_sign_extended; - if (xi.len + yi.len == 2) + if (__builtin_expect (xi.len + yi.len == 2, true)) { val[0] = xi.ulow () & ~yi.ulow (); result.set_len (1, is_sign_extended); @@ -2170,7 +2170,7 @@ wi::bit_or (const T1 &x, const T2 &y) WIDE_INT_REF_FOR (T1) xi (x, precision); WIDE_INT_REF_FOR (T2) yi (y, precision); bool is_sign_extended = xi.is_sign_extended && yi.is_sign_extended; - if (xi.len + yi.len == 2) + if (__builtin_expect (xi.len + yi.len == 2, true)) { val[0] = xi.ulow () | yi.ulow (); result.set_len (1, is_sign_extended); @@ -2191,7 +2191,7 @@ wi::bit_or_not (const T1 &x, const T2 &y WIDE_INT_REF_FOR (T1) xi (x, precision); WIDE_INT_REF_FOR (T2) yi (y, precision); bool is_sign_extended = xi.is_sign_extended && yi.is_sign_extended; - if (xi.len + yi.len == 2) + if (__builtin_expect (xi.len + yi.len == 2, true)) { val[0] = xi.ulow () | ~yi.ulow (); result.set_len (1, is_sign_extended); @@ -2212,7 +2212,7 @@ wi::bit_xor (const T1 &x, const T2 &y) WIDE_INT_REF_FOR (T1) xi (x, precision); WIDE_INT_REF_FOR (T2) yi (y, precision); bool is_sign_extended = xi.is_sign_extended && yi.is_sign_extended; - if (xi.len + yi.len == 2) + if (__builtin_expect (xi.len + yi.len == 2, true)) { val[0] = xi.ulow () ^ yi.ulow (); result.set_len (1, is_sign_extended); @@ -2248,7 +2248,7 @@ wi::add (const T1 &x, const T2 &y) HOST_BITS_PER_WIDE_INT are relatively rare and there's not much point handling them inline. */ else if (STATIC_CONSTANT_P (precision > HOST_BITS_PER_WIDE_INT) - && xi.len + yi.len == 2) + && __builtin_expect (xi.len + yi.len == 2, true)) { unsigned HOST_WIDE_INT xl = xi.ulow (); unsigned HOST_WIDE_INT yl = yi.ulow (); @@ -2323,7 +2323,7 @@ wi::sub (const T1 &x, const T2 &y) HOST_BITS_PER_WIDE_INT are relatively rare and there's not much point handling them inline. */ else if (STATIC_CONSTANT_P (precision > HOST_BITS_PER_WIDE_INT) - && xi.len + yi.len == 2) + && __builtin_expect (xi.len + yi.len == 2, true)) { unsigned HOST_WIDE_INT xl = xi.ulow (); unsigned HOST_WIDE_INT yl = yi.ulow ();