i386: Add define_insn_and_split patterns for btrl [PR96938]

i386: Add define_insn_and_split patterns for btrl [PR96938]

In the following testcase we only optimize f2 and f7 to btrl, although we
should optimize that way all of the functions.  The problem is the type
demotion/narrowing (which is performed solely during the generic folding and
not later), without it we see the AND performed in SImode and match it as
btrl, but with it while the shifts are still performed in SImode, the
AND is already done in QImode or HImode low part of the shift.

2021-01-13  Jakub Jelinek  <jakub@redhat.com>

	PR target/96938
	* config/i386/i386.md (*btr<mode>_1, *btr<mode>_2): New
	define_insn_and_split patterns.
	(splitter after *btr<mode>_2): New splitter.

	* gcc.target/i386/pr96938.c: New test.