i386: Use bzhi for x & ((1 << y) - 1) or x & ((1U << y) - 1) [PR93346]

i386: Use bzhi for x & ((1 << y) - 1) or x & ((1U << y) - 1) [PR93346]

The bzhi patterns are quite complicated because they need to accurately
describe the behavior of the instruction for all input values.
The following patterns are simple and make bzhi recognizable even for
cases where not all input values are valid, because the user used
a shift, in which case the low 8 bit of the last operand need to be in
between 0 and precision-1.

2020-01-23  Jakub Jelinek  <jakub@redhat.com>

	PR target/93346
	* config/i386/i386.md (*bmi2_bzhi_<mode>3_2, *bmi2_bzhi_<mode>3_3):
	New define_insn patterns.

	* gcc.target/i386/pr93346.c: New test.