x86: Tune Skylake, Cannonlake and Icelake as Haswell

x86: Tune Skylake, Cannonlake and Icelake as Haswell

r259399, which added PROCESSOR_SKYLAKE, disabled many x86 optimizations
which are enabled by PROCESSOR_HASWELL.  As the result, -mtune=skylake
generates slower codes on Skylake than before.  The same also applies
to Cannonlake and Icelak tuning.

This patch changes -mtune={skylake|cannonlake|icelake} to tune like
-mtune=haswell for until their tuning is properly adjusted. It also
enables -mprefer-vector-width=256 for -mtune=haswell, which has no
impact on codegen when AVX512 isn't enabled.

Performance impacts on SPEC CPU 2017 rate with 1 copy using

-march=native -mfpmath=sse -O2 -m64

are

1. On Broadwell server:

500.perlbench_r		-0.56%
502.gcc_r		-0.18%
505.mcf_r		0.24%
520.omnetpp_r		0.00%
523.xalancbmk_r		-0.32%
525.x264_r		-0.17%
531.deepsjeng_r		0.00%
541.leela_r		0.00%
548.exchange2_r		0.12%
557.xz_r		0.00%
Geomean			0.00%

503.bwaves_r		0.00%
507.cactuBSSN_r		0.21%
508.namd_r		0.00%
510.parest_r		0.19%
511.povray_r		-0.48%
519.lbm_r		0.00%
521.wrf_r		0.28%
526.blender_r		0.19%
527.cam4_r		0.39%
538.imagick_r		0.00%
544.nab_r		-0.36%
549.fotonik3d_r		0.51%
554.roms_r		0.00%
Geomean			0.17%

On Skylake client:

500.perlbench_r		0.96%
502.gcc_r		0.13%
505.mcf_r		-1.03%
520.omnetpp_r		-1.11%
523.xalancbmk_r		1.02%
525.x264_r		0.50%
531.deepsjeng_r		2.97%
541.leela_r		0.50%
548.exchange2_r		-0.95%
557.xz_r		2.41%
Geomean			0.56%

503.bwaves_r		0.49%
507.cactuBSSN_r		3.17%
508.namd_r		4.05%
510.parest_r		0.15%
511.povray_r		0.80%
519.lbm_r		3.15%
521.wrf_r		10.56%
526.blender_r		2.97%
527.cam4_r		2.36%
538.imagick_r		46.40%
544.nab_r		2.04%
549.fotonik3d_r		0.00%
554.roms_r		1.27%
Geomean			5.49%

On Skylake server:

500.perlbench_r		0.71%
502.gcc_r		-0.51%
505.mcf_r		-1.06%
520.omnetpp_r		-0.33%
523.xalancbmk_r		-0.22%
525.x264_r		1.72%
531.deepsjeng_r		-0.26%
541.leela_r		0.57%
548.exchange2_r		-0.75%
557.xz_r		-1.28%
Geomean			-0.21%

503.bwaves_r		0.00%
507.cactuBSSN_r		2.66%
508.namd_r		3.67%
510.parest_r		1.25%
511.povray_r		2.26%
519.lbm_r		1.69%
521.wrf_r		11.03%
526.blender_r		3.39%
527.cam4_r		1.69%
538.imagick_r		64.59%
544.nab_r		-0.54%
549.fotonik3d_r		2.68%
554.roms_r		0.00%
Geomean			6.19%

This patch improves -march=native performance on Skylake up to 60% and
leaves -march=native performance unchanged on Haswell.

gcc/

	Backport from mainline
	2018-07-13  H.J. Lu  <hongjiu.lu@intel.com>
		    Sunil K Pandey  <sunil.k.pandey@intel.com>

	PR target/84413
	* config/i386/i386.c (m_CORE_AVX512): New.
	(m_CORE_AVX2): Likewise.
	(m_CORE_ALL): Add m_CORE_AVX2.
	* config/i386/x86-tune.def: Replace m_HASWELL with m_CORE_AVX2.
	Replace m_SKYLAKE_AVX512 with m_CORE_AVX512 on avx256_optimal
	and remove the rest of m_SKYLAKE_AVX512.

gcc/testsuite/

	Backport from mainline
	2018-07-13  H.J. Lu  <hongjiu.lu@intel.com>
		    Sunil K Pandey  <sunil.k.pandey@intel.com>

	PR target/84413
	* gcc.target/i386/pr84413-1.c: New test.
	* gcc.target/i386/pr84413-2.c: Likewise.
	* gcc.target/i386/pr84413-3.c: Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-8-branch@262650 138bc75d-0d04-0410-961f-82ee72b054a4