i386: Optimize carry flag comparisons a bit

i386: Optimize carry flag comparisons a bit

In ix86_int_compare, opportunistically swap operands of GTU and LEU comparisons
to emit carry flag comparison, with the expectation that the comparison will
combine to *add<mode>3_carry_0 or *sub<mode>3_carry_0 insn pattern.

Do not use ix86_expand_carry_flag_compare because this function prefers
carry flag comparisons too much - it forces the constants into registers
and/or emits additional arithmetic instructions to convert simple
comparisons into carry flag comparisons - but simply swap operands to
convert GTU and LEU comparisons into GEU and LTU ones.

Also, change the insn predicates of *add<mode>3_carry_0 and
*sub<mode>3_carry_0 insn patterns to allow more combine opportunities
with memory operands.

2021-04-29  Uroš Bizjak  <ubizjak@gmail.com>

gcc/
	* config/i386/i386-expand.c (ix86_expand_int_compare):
	Swap operands of GTU and LEU comparison to emit carry flag comparison.
	* config/i386/i386.md (*add<mode>3_carry_0): Change insn
	predicate to allow more combine opportunities with memory operands.
	(*sub<mode>3_carry_0): Ditto.