...well, still HOST_BITS_PER_WIDE_INT-1 officially, until Richard's patches.
Caught by a boostrap-ubsan on wide-int. Tested on x86_64-linux-gnu and committed as obvious. Richard gcc/ * hwint.h (zext_hwi): Fix signed overflow for prec == 63. Index: gcc/hwint.h =================================================================== --- gcc/hwint.h 2014-01-03 15:06:18.841058787 +0000 +++ gcc/hwint.h 2014-05-02 16:31:44.987263123 +0100 @@ -344,7 +344,7 @@ zext_hwi (unsigned HOST_WIDE_INT src, un else { gcc_checking_assert (prec < HOST_BITS_PER_WIDE_INT); - return src & (((HOST_WIDE_INT) 1 << prec) - 1); + return src & (((unsigned HOST_WIDE_INT) 1 << prec) - 1); } }