libwebp simd code not properly built with Cmake build system

[Ozkan Sezer]

As the title says, e.g. with i686 + sse2 / sse4.1: SIMD build flags
aren't properly passed to individual SIMD-specific sources in cmake
E.g. for SSE2: the src checks two different macros, WEBP_USE_SSE2
and WEBP_HAVE_SSE2. The generated config.h defines WEBP_HAVE_SSE2
but since -msse2 isn't passed to sse2-specific sources and since
the compiler doesn't doesn't default to SSE2 by default (at least
that is the case with my toolchain) src/dsp/cpu.h does not define
WEBP_USE_SSE2, and certain sources doesn't include SIMD paths as a
result (sharpyuv_sse2.c.o is an empty object for me, for example.)
Autotools does it just right, see individual Makefile.am files for
details.

For the time being, I will be using autotools when building windows
dlls (and when building sharpyuv for libavif.) For that, I created
the attached patch while I was there, which I'll be pushing shortly:
0001-build-fixes-updates.patch.txt

Any improvements to cmake side requires @madebr I guess. Or, if we
don't want to bother, we can close this.

[Ozkan Sezer]

I may be wrong about the whole tree: sharpyuv is certainly affected though.

EDIT: Yes, looks like only sharpyuv is affected..

[Ozkan Sezer]

@madebr: Is the following correct?

diff --git a/cmake/cpu.cmake b/cmake/cpu.cmake
index 7513ca8..20ae612 100644
--- a/cmake/cpu.cmake
+++ b/cmake/cpu.cmake
@@ -107,6 +107,7 @@ foreach(I_SIMD RANGE ${WEBP_SIMD_FLAGS_RANGE})
   # 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}/../"
+       "sharpyuv/*${WEBP_SIMD_FILE_EXTENSION}"
        "src/dsp/*${WEBP_SIMD_FILE_EXTENSION}")
   if(WEBP_HAVE_${WEBP_SIMD_FLAG})
     # Memorize the file and flags.

[Anonymous Maarten]

Adding sources won't do anything, as the linker can resolve all missing links right now.
Does the following patch fix your intel issue?

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -69,6 +69,20 @@ if(WIN32)
   option(WEBP_UNICODE "Build Unicode executables." ON)
 endif()
 
+set(WEBP_HAVE_SSE2 0)
+set(WEBP_HAVE_SSE41 0)
+include(CheckCCompilerFlag)
+check_c_compiler_flag("-msse2" COMPILER_SUPPORTS_-msse2)
+if(COMPILER_SUPPORTS_-msse2)
+  set(WEBP_HAVE_SSE2 1)
+  add_compile_options(-msse2)
+  check_c_compiler_flag("-msse4.1" COMPILER_SUPPORTS_-msse4.1)
+  if(COMPILER_SUPPORTS_-msse4.1)
+    set(WEBP_HAVE_SSE41 1)
+    add_compile_options(-msse4.1)
+  endif()
+endif()
+
 if(WEBP_BUILD_WEBP_JS)
   set(WEBP_BUILD_ANIM_UTILS OFF)

[Ozkan Sezer]

No, that's not the issue. The part of the cmake'ry I referenced above does check for simd sources and adds the necessary simd compiler flags if available, but it does so only for the ones under src/dsp/. Adding sharpyuv/ glob there does fix the issue; however I am not sure whether or not it is correct in terms of cmake, i.e. I am not sure what the file(GLOB ....) does with "${CMAKE_CURRENT_LIST_DIR}/../": Should it instead be like the following??

diff --git a/cmake/cpu.cmake b/cmake/cpu.cmake
index 7513ca8..c2fae13 100644
--- a/cmake/cpu.cmake
+++ b/cmake/cpu.cmake
@@ -106,8 +106,9 @@ foreach(I_SIMD RANGE ${WEBP_SIMD_FLAGS_RANGE})
   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/*${WEBP_SIMD_FILE_EXTENSION}")
+  file(GLOB SIMD_FILES
+   "${CMAKE_CURRENT_LIST_DIR}/../sharpyuv/*${WEBP_SIMD_FILE_EXTENSION}"
+   "${CMAKE_CURRENT_LIST_DIR}/../src/dsp/*${WEBP_SIMD_FILE_EXTENSION}")
   if(WEBP_HAVE_${WEBP_SIMD_FLAG})
     # Memorize the file and flags.
     foreach(FILE ${SIMD_FILES})

[Anonymous Maarten]

Yes, your change is fine. When I compile with -DCMAKE_C_FLAGS="-m32 -march=i486", and add

#else
#error no sse2
#endif

to sharpyuv/sharpyuv_sse2.c, it fails to build.
With your changes, it builds.

[Ozkan Sezer]

With your changes, it builds.

Thanks. But, which patch is the correct one? Is it the one from #423 (comment) or the one from #423 (comment) ?

[Anonymous Maarten]

I tested both, and they both work.
The cpu.cmake script sets variables, that are used by the main CMakeLists.txt.
What matters is that the paths are relative to this main script.

That said, the 2nd approach is safer.
Alternatively, you can also do:

+  file(GLOB SIMD_FILES
+   "${PROJECT_SOURE_DIR}/sharpyuv/*${WEBP_SIMD_FILE_EXTENSION}"
+   "${PROJECT_SOURE_DIR}/src/dsp/*${WEBP_SIMD_FILE_EXTENSION}")

PROJECT_SOURCE_DIR is the folder of the most recent call to project.

[Ozkan Sezer]

OK, applied my second patch for now. Please feel free to revise / improve further.

[Anonymous Maarten]

I'd even say the patch isfit for upstreaming.
The steps don't look too hard: https://github.com/webmproject/libwebp/blob/main/CONTRIBUTING.md#sending-patches

[Ozkan Sezer]

I'd even say the patch isfit for upstreaming. The steps don't look too hard: https://github.com/webmproject/libwebp/blob/main/CONTRIBUTING.md#sending-patches

Done. (Pulled my hair a lot when trying to upload but figured it out eventually.)