openmp: Improve #pragma omp simd vectorization

openmp: Improve #pragma omp simd vectorization

As mentioned earlier, the vectorizer punts on vectorization of loops with non-constant
steps.  As for OpenMP loops it is by the language restriction always possible to compute
the number of loop iterations before the loop, this change helps those cases
by computing it and using an alternate IV that iterates from 0 to < niterations with
step of 1 next to the normal IV which will be just linear in that.

List of functions where we compared to current trunk vectorize some loops where we
previously didn't (for c-c++-common only listing the C function names, both C and C++
are affected though):

gcc/testsuite/gcc.dg/vect/vect-simd-17.c doit
gcc/testsuite/gcc.dg/vect/vect-simd-18.c foo
gcc/testsuite/gcc.dg/vect/vect-simd-19.c foo
gcc/testsuite/gcc.dg/vect/vect-simd-20.c foo
libgomp/testsuite/libgomp.c-c++-common/for-2.c f3_f_simd_auto
libgomp/testsuite/libgomp.c-c++-common/for-2.c f3_f_simd_guided32
libgomp/testsuite/libgomp.c-c++-common/for-2.c f3_f_simd_runtime
libgomp/testsuite/libgomp.c-c++-common/for-2.c f3_f_simd_static
libgomp/testsuite/libgomp.c-c++-common/for-2.c f3_f_simd_static32
libgomp/testsuite/libgomp.c-c++-common/for-2.c f3_pf_simd_auto._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-2.c f3_pf_simd_guided32._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-2.c f3_pf_simd_runtime._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-2.c f3_pf_simd_static32._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-2.c f3_pf_simd_static._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-2.c f3_simd_normal
libgomp/testsuite/libgomp.c-c++-common/for-2.c f5_simd_normal
libgomp/testsuite/libgomp.c-c++-common/for-2.c f6_simd_normal
libgomp/testsuite/libgomp.c-c++-common/for-3.c f3_dpfs_auto._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-3.c f3_dpfs_ds128_auto._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-3.c f3_dpfs_ds128_guided32._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-3.c f3_dpfs_ds128_runtime._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-3.c f3_dpfs_ds128_static32._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-3.c f3_dpfs_ds128_static._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-3.c f3_dpfs_guided32._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-3.c f3_dpfs_runtime._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-3.c f3_dpfs_static32._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-3.c f3_dpfs_static._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-3.c f3_ds_ds128_normal
libgomp/testsuite/libgomp.c-c++-common/for-3.c f3_ds_normal
libgomp/testsuite/libgomp.c-c++-common/for-4.c f3_taskloop_simd_normal._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_tpf_simd_auto._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_tpf_simd_guided32._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_tpf_simd_runtime._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_tpf_simd_static32._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_tpf_simd_static._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_t_simd_normal._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_ttdpfs_auto._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_ttdpfs_ds128_auto._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_ttdpfs_ds128_guided32._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_ttdpfs_ds128_runtime._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_ttdpfs_ds128_static32._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_ttdpfs_ds128_static._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_ttdpfs_guided32._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_ttdpfs_runtime._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_ttdpfs_static32._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_ttdpfs_static._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_ttds_ds128_normal._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-5.c f3_ttds_normal._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-5.c f5_t_simd_normal._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-5.c f6_t_simd_normal._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-6.c f3_tdpfs_auto._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-6.c f3_tdpfs_ds128_auto._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-6.c f3_tdpfs_ds128_guided32._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-6.c f3_tdpfs_ds128_runtime._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-6.c f3_tdpfs_ds128_static32._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-6.c f3_tdpfs_ds128_static._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-6.c f3_tdpfs_guided32._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-6.c f3_tdpfs_runtime._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-6.c f3_tdpfs_static32._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-6.c f3_tdpfs_static._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-6.c f3_tds_ds128_normal._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-6.c f3_tds_normal._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-14.c f3_dpfs_auto._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-14.c f3_dpfs_ds128_auto._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-14.c f3_dpfs_ds128_guided32._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-14.c f3_dpfs_ds128_runtime._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-14.c f3_dpfs_ds128_static32._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-14.c f3_dpfs_ds128_static._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-14.c f3_dpfs_guided32._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-14.c f3_dpfs_runtime._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-14.c f3_dpfs_static32._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-14.c f3_dpfs_static._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-14.c f3_ds_ds128_normal
libgomp/testsuite/libgomp.c-c++-common/for-14.c f3_ds_normal
libgomp/testsuite/libgomp.c-c++-common/for-15.c f3_tdpfs_auto._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-15.c f3_tdpfs_ds128_auto._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-15.c f3_tdpfs_ds128_guided32._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-15.c f3_tdpfs_ds128_runtime._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-15.c f3_tdpfs_ds128_static32._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-15.c f3_tdpfs_ds128_static._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-15.c f3_tdpfs_guided32._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-15.c f3_tdpfs_runtime._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-15.c f3_tdpfs_static32._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-15.c f3_tdpfs_static._omp_fn.1
libgomp/testsuite/libgomp.c-c++-common/for-15.c f3_tds_ds128_normal._omp_fn.0
libgomp/testsuite/libgomp.c-c++-common/for-15.c f3_tds_normal._omp_fn.0

2020-09-26  Jakub Jelinek  <jakub@redhat.com>

	* omp-expand.c (expand_omp_simd): Help vectorizer for the collapse == 1
	and non-composite collapse > 1 case with non-constant innermost loop
	step by precomputing number of iterations before loop and using an
	alternate IV from 0 to number of iterations - 1 with step of 1.

	* gcc.dg/vect/vect-simd-17.c: Expect 11 or more vectorized loops.
	* gcc.dg/vect/vect-simd-18.c: New test.
	* gcc.dg/vect/vect-simd-19.c: New test.
	* gcc.dg/vect/vect-simd-20.c: New test.