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

[Roger Sayle]

"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 when
optimizing for speed, but both use and/mul when optimizing for
size.

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.

This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-m32},
with no new failures.  Ok for mainline?


2022-05-24  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.

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


Thanks in advance,
Roger
--

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