Use the correct AVX flags for Windows builds

generate_gypi.sh

 #!/bin/bash -e
 #
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This script is used to generate .gypi, .gni files and files in the
 # config/platform directories needed to build libvpx.
 # Every time libvpx source code is updated just run this script.
 #
@@ skipping 99 matching lines @@
   echo "        ['use_lto==1', {" >> "$2"
   echo "          'cflags!': [" >> "$2"
   echo "            '-flto'," >> "$2"
   echo "            '-ffat-lto-objects'," >> "$2"
   echo "          ]," >> "$2"
   echo "        }]," >> "$2"
   echo "      ]," >> "$2"
   fi
   echo "      'cflags': [ '-m$4', ]," >> "$2"
   echo "      'xcode_settings': { 'OTHER_CFLAGS': [ '-m$4' ] }," >> "$2"
   if [[ $4 == avx* ]]; then

[Nico, 2015/01/23 02:57:12]

Shouldn't this block cover that already?

[Johann, 2015/01/23 03:26:35]

Well, this block covers using "EnableEnhancedInstructionSet" which I wasn't sure
was used by clang. Rather than duplicate the code below and add a condition for
clang==1 and AdditionalOptions -mavx2, it seemed easiest to add the avx2 flag
below.

It also tops out at AVX, but msvc doesn't seem to care and still accepts the
avx2 instructions (see conversation here:
https://codereview.chromium.org/817293008/)

[Nico, 2015/01/23 19:14:29]

On Windows, we use clang through clang-cl, a compiler driver that aims to be
commandline-compatible with cl.exe (msvc's compiler). In theory, clang will use
all the Windows settings from gyp. (In practice, this is true too.)
You want /arch:AVX2, in gn too. I think the linked-to patch isn't right, if you
want AVX2.

One issue is that gyp didn't expose this. I fixed this in
https://codereview.chromium.org/872643002/ , and once
https://codereview.chromium.org/873793002/ is in, you can say '5' for AVX2 in
gyp files.

   echo "      'msvs_settings': {" >> "$2"
   echo "        'VCCLCompilerTool': {" >> "$2"
   echo "          'EnableEnhancedInstructionSet': '3', # /arch:AVX" >> "$2"

[Nico, 2015/01/23 02:57:12]

I think the problem here is that this unconditionally passes '3'. First, gyp
needs to learn which number corresponds to AVX2 here
https://code.google.com/p/chromium/codesearch#chromium/src/tools/gyp/pylib/gy...
(I'll take care of that), and then this needs to use '3' for AVX and whatever
the number for AVX2 is for AVX2. Then everything should work.

[Johann, 2015/01/23 03:26:35]

We only currently have avx2 code. We can switch the if statement to == avx2 if
that is cleaner. See the other comment for avx/avx2.

[Nico, 2015/01/23 19:14:28]

If this is only for avx2, then I'd change the statement to == avx2. If you
change the EnableEnhancedInstructionSet line to

  echo "          'EnableEnhancedInstructionSet': '5', # /arch:AVX2" >> "$2"

then everything works fine with clang – I just tested that locally.

(This will only work once https://codereview.chromium.org/873793002/ has
landed.)

   echo "        }," >> "$2"
   echo "      }," >> "$2"
-  elif [[ $4 == ssse3 || $4 == sse4.1 ]]; then
+  fi
+  if [[ $4 == ssse3 || $4 == sse4.1 || $4 == avx2 ]]; then
   echo "      'conditions': [" >> "$2"
   echo "        ['OS==\"win\" and clang==1', {" >> "$2"
   echo "          # cl.exe's /arch flag doesn't have a setting for SSSE3/4, and cl.exe" >> "$2"
-  echo "          # doesn't need it for intrinsics. clang-cl does need it, though." >> "$2"
+  echo "          # doesn't need it for intrinsics. There is an /arch flag for AVX2 but" >> "$2"
+  echo "          # clang-cl needs its own in the form of -mOPT." >> "$2"
   echo "          'msvs_settings': {" >> "$2"
   echo "            'VCCLCompilerTool': { 'AdditionalOptions': [ '-m$4' ] }," >> "$2"
   echo "          }," >> "$2"
   echo "        }]," >> "$2"
   echo "      ]," >> "$2"
   fi
   echo "    }," >> "$2"
 }
 
 
@@ skipping 372 matching lines @@
 make_clean
 make libvpx_srcs.txt target=libs $config > /dev/null
 convert_srcs_to_project_files libvpx_srcs.txt libvpx_srcs_generic
 
 echo "Remove temporary directory."
 cd $BASE_DIR
 rm -rf $TEMP_DIR
 
 # TODO(fgalligan): Is "--disable-fast-unaligned" needed on mipsel?
 # TODO(fgalligan): Can we turn on "--enable-realtime-only" for mipsel?