Improved handling of division/modulus in bit CCP.

Improved handling of division/modulus in bit CCP.

This patch implements support for TRUNC_MOD_EXPR and TRUNC_DIV_EXPR
in tree-ssa's bit CCP pass.  This is mostly for completeness, as the
VRP pass already provides better bounds for these operations, but
seeing mask values of all_ones in my debugging/instrumentation logs
seemed overly pessimistic.  With this patch, the expression X%10
has a nonzero bits of 0x0f (for unsigned X), likewise (X&1)/3 has
a known value of zero, and (X&3)/3 has a nonzero bits mask of 0x1.

2021-08-23  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* tree-ssa-ccp.c (bit_value_binop) [TRUNC_MOD_EXPR, TRUNC_DIV_EXPR]:
	Provide bounds for unsigned (and signed with non-negative operands)
	division and modulus.