add dec_wasm.c

stub + basic cmake support for targeting native code generation using
portable intrinsics / wasm (WebAssembly). integrating this into the
webp_js path will be left until the implementation is more complete.

Change-Id: I3e751b511f6d671da5ba8afc88ca412f31f097b0

CMakeLists.txt

@@ -4,6 +4,7 @@ project(libwebp C)
 
 # Options for coder / decoder executables.
 option(WEBP_ENABLE_SIMD "Enable any SIMD optimization." ON)
+option(WEBP_ENABLE_WASM "Enable WebAssembly optimizations." OFF)
 option(WEBP_BUILD_CWEBP "Build the cwebp command line tool." OFF)
 option(WEBP_BUILD_DWEBP "Build the dwebp command line tool." OFF)
 option(WEBP_BUILD_GIF2WEBP "Build the gif2webp conversion tool." OFF)
@@ -13,7 +14,7 @@ option(WEBP_BUILD_WEBP_JS "Emscripten build of webp.js." OFF)
 option(WEBP_EXPERIMENTAL_FEATURES "Build with experimental features." OFF)
 option(WEBP_ENABLE_SWAP_16BIT_CSP "Enable byte swap for 16 bit colorspaces." OFF)
 
-if(WEBP_BUILD_WEBP_JS)
+if(WEBP_BUILD_WEBP_JS OR WEBP_ENABLE_WASM)
   set(WEBP_ENABLE_SIMD OFF)
 endif()
 
@@ -37,6 +38,9 @@ string(REGEX MATCH "[0-9.]+" WEBP_VERSION ${SOURCE_FILE})
 if(WEBP_ENABLE_SWAP_16BIT_CSP)
   add_definitions(-DWEBP_SWAP_16BIT_CSP)
 endif()
+if(WEBP_ENABLE_WASM)
+  add_definitions(-DWEBP_USE_WASM)
+endif()
 
 ################################################################################
 # Android only.
@@ -162,9 +166,11 @@ math(EXPR WEBP_SIMD_FILES_TO_INCLUDE_RANGE
 foreach(I_FILE RANGE ${WEBP_SIMD_FILES_TO_INCLUDE_RANGE})
   list(GET WEBP_SIMD_FILES_TO_INCLUDE ${I_FILE} FILE)
   list(GET WEBP_SIMD_FLAGS_TO_INCLUDE ${I_FILE} SIMD_COMPILE_FLAG)
+  if(NOT ${SIMD_COMPILE_FLAG} STREQUAL "NOTFOUND")
     set_source_files_properties(${FILE} PROPERTIES
       COMPILE_FLAGS ${SIMD_COMPILE_FLAG}
     )
+  endif()
 endforeach()
 
 # Build the executables if asked for.

README.webp_js

@@ -31,6 +31,11 @@ using Emscripten and CMake.
  - that's it! Upon completion, you should have the webp.js and
    webp.js.mem files generated.
 
+ - Note this generates both webp_js and webp_wasm without any SIMD enabled due
+   to bugs with this toolchain associated with the SSE2 code.
+   -DWEBP_ENABLE_WASM is currently meant to generate native (x86, arm)
+   executables (dwebp, cwebp) and is incompatible with -DWEBP_BUILD_WEBP_JS.
+
 The callable JavaScript function is WebPToSDL(), which decodes a raw WebP
 bitstream into a canvas. See webp_js/index.html for a simple usage sample.
 

cmake/cpu.cmake

@@ -116,3 +116,13 @@ foreach(I_SIMD RANGE ${WEBP_SIMD_FLAGS_RANGE})
     endif()
   endif()
 endforeach()
+
+## Add *_wasm.c files if enabled.
+if(WEBP_ENABLE_WASM)
+  file(GLOB SIMD_FILES "${CMAKE_CURRENT_LIST_DIR}/../"
+    "src/dsp/*_wasm.c"
+  )
+  foreach(FILE ${SIMD_FILES})
+    list(APPEND WEBP_SIMD_FILES_TO_INCLUDE ${FILE})
+  endforeach()
+endif()

src/dsp/Makefile.am

@@ -3,6 +3,7 @@ noinst_LTLIBRARIES += libwebpdsp_sse2.la libwebpdspdecode_sse2.la
 noinst_LTLIBRARIES += libwebpdsp_sse41.la libwebpdspdecode_sse41.la
 noinst_LTLIBRARIES += libwebpdsp_neon.la libwebpdspdecode_neon.la
 noinst_LTLIBRARIES += libwebpdsp_msa.la libwebpdspdecode_msa.la
+noinst_LTLIBRARIES += libwebpdspdecode_wasm.la
 
 if BUILD_LIBWEBPDECODER
   noinst_LTLIBRARIES += libwebpdspdecode.la
@@ -96,6 +97,10 @@ libwebpdspdecode_msa_la_SOURCES += upsampling_msa.c
 libwebpdspdecode_msa_la_CPPFLAGS = $(libwebpdsp_msa_la_CPPFLAGS)
 libwebpdspdecode_msa_la_CFLAGS = $(libwebpdsp_msa_la_CFLAGS)
 
+# WASM is not fully integrated into configure; the addition here keeps source
+# extraction by cmake simple.
+libwebpdspdecode_wasm_la_SOURCES = dec_wasm.c
+
 libwebpdsp_sse2_la_SOURCES =
 libwebpdsp_sse2_la_SOURCES += argb_sse2.c
 libwebpdsp_sse2_la_SOURCES += cost_sse2.c

src/dsp/cpu.c

@@ -217,6 +217,12 @@ static int mipsCPUInfo(CPUFeature feature) {
 
 }
 VP8CPUInfo VP8GetCPUInfo = mipsCPUInfo;
+#elif defined(WEBP_USE_WASM)
+static int wasmCPUInfo(CPUFeature feature) {
+  if (feature != kWASM) return 0;
+  return 1;
+}
+VP8CPUInfo VP8GetCPUInfo = wasmCPUInfo;
 #else
 VP8CPUInfo VP8GetCPUInfo = NULL;
 #endif

src/dsp/dec.c

@@ -700,6 +700,7 @@ extern void VP8DspInitNEON(void);
 extern void VP8DspInitMIPS32(void);
 extern void VP8DspInitMIPSdspR2(void);
 extern void VP8DspInitMSA(void);
+extern void VP8DspInitWASM(void);
 
 static volatile VP8CPUInfo dec_last_cpuinfo_used =
     (VP8CPUInfo)&dec_last_cpuinfo_used;
@@ -789,6 +790,11 @@ WEBP_TSAN_IGNORE_FUNCTION void VP8DspInit(void) {
     if (VP8GetCPUInfo(kMSA)) {
       VP8DspInitMSA();
     }
+#endif
+#if defined(WEBP_USE_WASM)
+    if (VP8GetCPUInfo(kWASM)) {
+      VP8DspInitWASM();
+    }
 #endif
   }
   dec_last_cpuinfo_used = VP8GetCPUInfo;

src/dsp/dec_wasm.c

@@ -0,0 +1,29 @@
+// Copyright 2017 Google Inc. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+// -----------------------------------------------------------------------------
+//
+// WebAssembly (WASM) version of some decoding functions.
+//
+
+#include "./dsp.h"
+
+#if defined(WEBP_USE_WASM)
+
+//------------------------------------------------------------------------------
+// Entry point
+
+extern void VP8DspInitWASM(void);
+
+WEBP_TSAN_IGNORE_FUNCTION void VP8DspInitWASM(void) {
+}
+
+#else  // !WEBP_USE_WASM
+
+WEBP_DSP_INIT_STUB(VP8DspInitWASM)
+
+#endif  // WEBP_USE_WASM

src/dsp/dsp.h

@@ -42,8 +42,9 @@ extern "C" {
 # define __has_builtin(x) 0
 #endif
 
-// for now, none of the optimizations below are available in emscripten
-#if !defined(EMSCRIPTEN)
+// For now, none of the optimizations below are available in emscripten.
+// WebAssembly overrides native optimizations.
+#if !(defined(EMSCRIPTEN) || defined(WEBP_USE_WASM))
 
 #if defined(_MSC_VER) && _MSC_VER > 1310 && \
     (defined(_M_X64) || defined(_M_IX86))
@@ -144,7 +145,8 @@ typedef enum {
   kNEON,
   kMIPS32,
   kMIPSdspR2,
-  kMSA
+  kMSA,
+  kWASM
 } CPUFeature;
 // returns true if the CPU supports the feature.
 typedef int (*VP8CPUInfo)(CPUFeature feature);