rs6000: Fix _mm_slli_epi{32,64} for shift values 16 through 31 and negative (PR84302)

rs6000: Fix _mm_slli_epi{32,64} for shift values 16 through 31 and negative (PR84302)

The powerpc versions of _mm_slli_epi32 and __mm_slli_epi64 in emmintrin.h
do not properly handle shift values between 16 and 31, inclusive.
These are setting up the shift with vec_splat_s32, which only accepts
*5 bit signed* shift values, or a range of -16 to 15.  Values above 15
produce an error:

  error: argument 1 must be a 5-bit signed literal

Fix is to effectively reduce the range for which vec_splat_s32 is used
to < 32 and use vec_splats otherwise.

Also, __mm_slli_epi{16,32,64}, when given a negative shift value,
should always return a vector of {0}.

	PR target/83402
	* config/rs6000/emmintrin.h (_mm_slli_epi{16,32,64}):
	Ensure that vec_splat_s32 is only called with 0 <= shift < 16.
	Ensure negative shifts result in {0}.

gcc/testsuite/
	PR target/83402
	* gcc.target/powerpc/sse2-psllw-1.c: Refactor and add tests for
	several values:  positive, negative, and zero.
	* gcc.target/powerpc/sse2-pslld-1.c: Same.
	* gcc.target/powerpc/sse2-psllq-1.c: Same.

From-SVN: r259380