widening_mul: Pattern recognize unsigned multiplication with overflow check [PR95852]

widening_mul: Pattern recognize unsigned multiplication with overflow check [PR95852]

The following patch pattern recognizes some forms of multiplication followed
by overflow check through division by one of the operands compared to the
other one, with optional removal of guarding non-zero check for that operand
if possible.  The patterns are replaced with effectively
__builtin_mul_overflow or __builtin_mul_overflow_p.  The testcases cover 64
different forms of that.

2021-01-11  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/95852
	* tree-ssa-math-opts.c (maybe_optimize_guarding_check): New function.
	(uaddsub_overflow_check_p): Renamed to ...
	(arith_overflow_check_p): ... this.  Handle also multiplication
	with overflow check.
	(match_uaddsub_overflow): Renamed to ...
	(match_arith_overflow): ... this.  Add cfg_changed argument.  Handle
	also multiplication with overflow check.  Adjust function comment.
	(math_opts_dom_walker::after_dom_children): Adjust callers.  Call
	match_arith_overflow also for MULT_EXPR.

	* gcc.target/i386/pr95852-1.c: New test.
	* gcc.target/i386/pr95852-2.c: New test.