Merge "cmake: fix per-file assembly flags"

cmake/cpu.cmake

@@ -31,9 +31,17 @@ endfunction()
 set(WEBP_SIMD_FLAGS "SSE41;SSE2;MIPS32;MIPS_DSP_R2;NEON;MSA")
 set(WEBP_SIMD_FILE_EXTENSIONS
     "_sse41.c;_sse2.c;_mips32.c;_mips_dsp_r2.c;_neon.c;_msa.c")
-if(MSVC)
+if(MSVC AND CMAKE_C_COMPILER_ID STREQUAL "MSVC")
-  # MSVC does not have a SSE4 flag but AVX support implies SSE4 support.
+  # With at least Visual Studio 12 (2013)+ /arch is not necessary to build SSE2
+  # or SSE4 code unless a lesser /arch is forced. MSVC does not have a SSE4
+  # flag, but an AVX one. Using that with SSE4 code risks generating illegal
+  # instructions when used on machines with SSE4 only. The flags are left for
+  # older (untested) versions to avoid any potential compatibility issues.
+  if(MSVC_VERSION GREATER_EQUAL 1800 AND NOT CMAKE_C_FLAGS MATCHES "/arch:")
+    set(SIMD_ENABLE_FLAGS)
+  else()
     set(SIMD_ENABLE_FLAGS "/arch:AVX;/arch:SSE2;;;;")
+  endif()
   set(SIMD_DISABLE_FLAGS)
 else()
   set(SIMD_ENABLE_FLAGS
@@ -57,9 +65,14 @@ endif()
 
 list(LENGTH WEBP_SIMD_FLAGS WEBP_SIMD_FLAGS_LENGTH)
 math(EXPR WEBP_SIMD_FLAGS_RANGE "${WEBP_SIMD_FLAGS_LENGTH} - 1")
-unset(HIGHEST_SSE_FLAG)
 
 foreach(I_SIMD RANGE ${WEBP_SIMD_FLAGS_RANGE})
+  # With Emscripten 2.0.9 -msimd128 -mfpu=neon will enable NEON, but the
+  # source will fail to compile.
+  if(EMSCRIPTEN AND ${I_SIMD} GREATER_EQUAL 2)
+    break()
+  endif()
+
   list(GET WEBP_SIMD_FLAGS ${I_SIMD} WEBP_SIMD_FLAG)
 
   # First try with no extra flag added as the compiler might have default flags
@@ -67,7 +80,6 @@ foreach(I_SIMD RANGE ${WEBP_SIMD_FLAGS_RANGE})
   unset(WEBP_HAVE_${WEBP_SIMD_FLAG} CACHE)
   cmake_push_check_state()
   set(CMAKE_REQUIRED_FLAGS)
-  if(NOT simd_found)
   webp_check_compiler_flag(${WEBP_SIMD_FLAG} ${WEBP_ENABLE_SIMD})
   if(NOT WEBP_HAVE_${WEBP_SIMD_FLAG})
     list(GET SIMD_ENABLE_FLAGS ${I_SIMD} SIMD_COMPILE_FLAG)
@@ -77,33 +89,24 @@ foreach(I_SIMD RANGE ${WEBP_SIMD_FLAGS_RANGE})
     set(CMAKE_REQUIRED_FLAGS ${SIMD_COMPILE_FLAG})
     webp_check_compiler_flag(${WEBP_SIMD_FLAG} ${WEBP_ENABLE_SIMD})
   else()
-      if(MSVC)
+    if(MSVC AND SIMD_ENABLE_FLAGS)
+      # The detection for SSE2/SSE4 support under MSVC is based on the compiler
+      # version so e.g., clang-cl will require flags to enable the assembly.
       list(GET SIMD_ENABLE_FLAGS ${I_SIMD} SIMD_COMPILE_FLAG)
     else()
       set(SIMD_COMPILE_FLAG " ")
     endif()
   endif()
-  elseif(${I_SIMD} LESS 2)
-    set(WEBP_HAVE_${WEBP_SIMD_FLAG} 1)
-  endif()
   # Check which files we should include or not.
   list(GET WEBP_SIMD_FILE_EXTENSIONS ${I_SIMD} WEBP_SIMD_FILE_EXTENSION)
   file(GLOB SIMD_FILES "${CMAKE_CURRENT_LIST_DIR}/../"
             "src/dsp/*${WEBP_SIMD_FILE_EXTENSION}")
   if(WEBP_HAVE_${WEBP_SIMD_FLAG})
-    if(${I_SIMD} LESS 2 AND NOT HIGHEST_SSE_FLAG)
-      set(HIGHEST_SSE_FLAG ${SIMD_COMPILE_FLAG})
-    endif()
     # Memorize the file and flags.
     foreach(FILE ${SIMD_FILES})
       list(APPEND WEBP_SIMD_FILES_TO_INCLUDE ${FILE})
-      if(${I_SIMD} LESS 2)
-        list(APPEND WEBP_SIMD_FLAGS_TO_INCLUDE ${HIGHEST_SSE_FLAG})
-      else()
       list(APPEND WEBP_SIMD_FLAGS_TO_INCLUDE ${SIMD_COMPILE_FLAG})
-      endif()
     endforeach()
-    set(simd_found 1)
   else()
     # Remove the file from the list.
     foreach(FILE ${SIMD_FILES})