With -mavx, for

$ cat foo.i
extern float f;
extern double d;
extern int i;

void
foo (void)
{
  d = f;
  f = i;
}

we need to generate

	vxorp[ds]	%xmmN, %xmmN, %xmmN
	...
	vcvtss2sd	f(%rip), %xmmN, %xmmX
	...
	vcvtsi2ss	i(%rip), %xmmN, %xmmY

to avoid partial XMM register stall.  This patch adds a pass to generate
a single

	vxorps		%xmmN, %xmmN, %xmmN

at entry of the nearest dominator for basic blocks with SF/DF conversions,
which is in the fake loop that contains the whole function, instead of
generating one

	vxorp[ds]	%xmmN, %xmmN, %xmmN

for each SF/DF conversion.

NB: The LCM algorithm isn't appropriate here since it may place a vxorps
inside the loop.  Simple testcase show this:

$ cat badcase.c

extern float f;
extern double d;

void
foo (int n, int k)
{
  for (int j = 0; j != n; j++)
    if (j < k)
      d = f;
}

It generates

    ...
    loop:
      if(j < k)
        vxorps    %xmm0, %xmm0, %xmm0
        vcvtss2sd f(%rip), %xmm0, %xmm0
      ...
    loopend
    ...

This is because LCM only works when there is a certain benifit.  But for
conditional branch, LCM wouldn't move

   vxorps  %xmm0, %xmm0, %xmm0

out of loop.  SPEC CPU 2017 on Intel Xeon with AVX512 shows:

1. The nearest dominator

|RATE			|Improvement|
|500.perlbench_r	| 0.55%	|
|538.imagick_r		| 8.43%	|
|544.nab_r		| 0.71%	|

2. LCM

|RATE			|Improvement|
|500.perlbench_r	| -0.76% |
|538.imagick_r		| 7.96%  |
|544.nab_r		| -0.13% |

Performance impacts of SPEC CPU 2017 rate on Intel Xeon with AVX512
using

-Ofast -flto -march=skylake-avx512 -funroll-loops

before

commit e739972ad6ad05e32a1dd5c29c0b950a4c4bd576
Author: uros <uros@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Thu Jan 31 20:06:42 2019 +0000

            PR target/89071
            * config/i386/i386.md (*extendsfdf2): Split out reg->reg
            alternative to avoid partial SSE register stall for TARGET_AVX.
            (truncdfsf2): Ditto.
            (sse4_1_round<mode>2): Ditto.

    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@268427 138bc75d-0d04-0410-961f-82ee72b054a4

are:

|INT RATE		|Improvement|
|500.perlbench_r	| 0.55%	|
|502.gcc_r		| 0.14%	|
|505.mcf_r		| 0.08%	|
|523.xalancbmk_r	| 0.18%	|
|525.x264_r		|-0.49%	|
|531.deepsjeng_r	|-0.04%	|
|541.leela_r		|-0.26%	|
|548.exchange2_r	|-0.3%	|
|557.xz_r		|BuildSame|

|FP RATE		|Improvement|
|503.bwaves_r	        |-0.29% |
|507.cactuBSSN_r	| 0.04%	|
|508.namd_r		|-0.74%	|
|510.parest_r		|-0.01%	|
|511.povray_r		| 2.23%	|
|519.lbm_r		| 0.1%	|
|521.wrf_r		| 0.49%	|
|526.blender_r		| 0.13%	|
|527.cam4_r		| 0.65%	|
|538.imagick_r		| 8.43%	|
|544.nab_r		| 0.71%	|
|549.fotonik3d_r	| 0.15%	|
|554.roms_r		| 0.08%	|

After commit e739972ad6ad05e32a1dd5c29c0b950a4c4bd576, on Skylake client,
impacts on 538.imagick_r with

-fno-unsafe-math-optimizations -march=native -Ofast -funroll-loops -flto

1. Size comparision:

before:

   text	   data	    bss	    dec	    hex	filename
2436377	   8352	   4528	2449257	 255f69 imagick_r

after:

   text	   data	    bss	    dec	    hex	filename
2425249	   8352	   4528	2438129	 2533f1 imagick_r

2. Number of vxorps:

before		after		difference
4948            4135            -19.66%

3. Performance improvement:

|RATE			|Improvement|
|538.imagick_r		| 5.5%  |

gcc/

2019-02-22  H.J. Lu  <hongjiu.lu@intel.com>
	    Hongtao Liu  <hongtao.liu@intel.com>
	    Sunil K Pandey  <sunil.k.pandey@intel.com>

	PR target/87007
	* config/i386/i386-passes.def: Add
	pass_remove_partial_avx_dependency.
	* config/i386/i386-protos.h
	(make_pass_remove_partial_avx_dependency): New.
	* config/i386/i386.c (make_pass_remove_partial_avx_dependency):
	New function.
	(pass_data_remove_partial_avx_dependency): New.
	(pass_remove_partial_avx_dependency): Likewise.
	(make_pass_remove_partial_avx_dependency): Likewise.
	* config/i386/i386.md (avx_partial_xmm_update): New attribute.
	(*extendsfdf2): Add avx_partial_xmm_update.
	(truncdfsf2): Likewise.
	(*float<SWI48:mode><MODEF:mode>2): Likewise.
	(SF/DF conversion splitters): Disabled for TARGET_AVX.

gcc/testsuite/

2019-02-22  H.J. Lu  <hongjiu.lu@intel.com>
	    Hongtao Liu  <hongtao.liu@intel.com>
	    Sunil K Pandey  <sunil.k.pandey@intel.com>

	PR target/87007
	* gcc.target/i386/pr87007-1.c: New test.
	* gcc.target/i386/pr87007-2.c: Likewise.

Co-Authored-By: Hongtao Liu <hongtao.liu@intel.com>
Co-Authored-By: Sunil K Pandey <sunil.k.pandey@intel.com>

From-SVN: r269119