Canonicalize X&-Y as X*Y in match.pd when Y is [0,1].

"For every pessimization, there's an equal and opposite optimization".

In the review of my original patch for PR middle-end/98865, Richard
Biener pointed out that match.pd shouldn't be transforming X*Y into
X&-Y as the former is considered cheaper by tree-ssa's cost model
(operator count).  A corollary of this is that we should instead be
transforming X&-Y into the cheaper X*Y as a preferred canonical form
(especially as RTL expansion now intelligently selects the appropriate
implementation based on the target's costs).

With this patch we now generate identical code for:
int foo(int x, int y) { return -(x&1) & y; }
int bar(int x, int y) { return (x&1) * y; }

specifically on x86_64-pc-linux-gnu both use and/neg/and with -O2,
but both use and/mul with -Os.

One minor wrinkle/improvement is that this patch includes three
additional optimizations (that account for the change in canonical
form) to continue to optimize PR92834 and PR94786.

2022-05-27  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* match.pd (match_zero_one_valued_p): New predicate.
	(mult @0 @1): Use zero_one_valued_p for optimization to the
	expression "bit_and @0 @1".
	(bit_and (negate zero_one_valued_p@0) @1): Optimize to MULT_EXPR.
	(plus @0 (mult (minus @1 @0) zero_one_valued_p@2)): New transform.
	(minus @0 (mult (minus @0 @1) zero_one_valued_p@2)): Likewise.
	(bit_xor @0 (mult (bit_xor @0 @1) zero_one_valued_p@2)): Likewise.
	Remove three redundant transforms obsoleted by the three above.

gcc/testsuite/ChangeLog
	* gcc.dg/pr98865.c: New test case.

0 files changed, 0 insertions, 0 deletions