Enable RVV support in CMake and Bazel for RISC-V targets

Enable RISC-V Vector (RVV) by default when building natively on RISC-V
platforms (such as SpacemiT K1/K3) using CMake and Bazel:
- CMakeLists.txt: Detect riscv64 and riscv32, probe compiler support
  for -march=rv64gcv / -march=rv32gcv, and append architecture flags
  with auto-vectorization disabled (-fno-vectorize -fno-slp-vectorize).
  Support custom architecture flags via -DRISCV_COMPILER_FLAGS and
  provide -DUSE_RVV=OFF to disable.
- BUILD.bazel: Add RVV_COPTS for @platforms//cpu:riscv64 and
  @platforms//cpu:riscv32 with -fno-vectorize.
- docs/getting_started.md: Document native SBC builds, custom targets
  (SiFive X280, Coral 32-bit Zve32x), Bazel, and Blaze commands.

Test: cmake build on host and simulated riscv64; clang cross-compile tests
Bug: none
Change-Id: Iecb20b73b2934b6477e7e0c71b3539a8251e4e8b
TAG=agy
CONV=2f28dd8a-c892-4c29-8aed-606afd090398
Reviewed-on: https://chromium-review.googlesource.com/c/libyuv/libyuv/+/8349493
Reviewed-by: richard winterton <rrwinterton@gmail.com>
Commit-Queue: Frank Barchard <fbarchard@google.com>

BUILD.bazel

@@ -56,7 +56,21 @@ PLATFORM_COPTS = select({
     "-DGOOGLE_COMMANDLINEFLAGS_FULL_API",
 ]
 
-ALL_COPTS = PLATFORM_COPTS
+RVV_COPTS = select({
+    "@platforms//cpu:riscv64": [
+        "-march=rv64gcv",
+        "-fno-vectorize",
+        "-fno-slp-vectorize",
+    ],
+    "@platforms//cpu:riscv32": [
+        "-march=rv32gcv",
+        "-fno-vectorize",
+        "-fno-slp-vectorize",
+    ],
+    "//conditions:default": [],
+})
+
+ALL_COPTS = PLATFORM_COPTS + RVV_COPTS
 
 ALL_NEON_COPTS = NEON_COPTS + PLATFORM_COPTS
 

CMakeLists.txt

@@ -139,6 +139,41 @@ int main(void) { return 0; }
       add_definitions(-DLIBYUV_DISABLE_SME)
     endif()
   endif()
+
+  if(arch_lowercase MATCHES "^riscv")
+    option(USE_RVV "Enable RISC-V Vector" ON)
+    if(USE_RVV)
+      if(NOT RISCV_COMPILER_FLAGS)
+        if(CMAKE_SIZEOF_VOID_P EQUAL 8 OR arch_lowercase STREQUAL "riscv64")
+          set(RISCV_COMPILER_FLAGS "-march=rv64gcv")
+        else()
+          set(RISCV_COMPILER_FLAGS "-march=rv32gcv")
+        endif()
+      endif()
+
+      include(CheckCSourceCompiles)
+      set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
+      set(OLD_CMAKE_TRY_COMPILE_TARGET_TYPE ${CMAKE_TRY_COMPILE_TARGET_TYPE})
+      set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} ${RISCV_COMPILER_FLAGS}")
+      set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
+      check_c_source_compiles("
+int main(void) { return 0; }
+      " CAN_COMPILE_RVV)
+      set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
+      set(CMAKE_TRY_COMPILE_TARGET_TYPE ${OLD_CMAKE_TRY_COMPILE_TARGET_TYPE})
+
+      if(CAN_COMPILE_RVV)
+        if(NOT CMAKE_C_FLAGS MATCHES "-march=" AND NOT CMAKE_C_FLAGS MATCHES "-mcpu=")
+          set(CMAKE_C_FLAGS "${RISCV_COMPILER_FLAGS} -fno-vectorize -fno-slp-vectorize ${CMAKE_C_FLAGS}")
+          set(CMAKE_CXX_FLAGS "${RISCV_COMPILER_FLAGS} -fno-vectorize -fno-slp-vectorize ${CMAKE_CXX_FLAGS}")
+        endif()
+      else()
+        add_definitions(-DLIBYUV_DISABLE_RVV)
+      endif()
+    else()
+      add_definitions(-DLIBYUV_DISABLE_RVV)
+    endif()
+  endif()
 endif()
 
 if(LOONGARCH64)

docs/getting_started.md

@@ -224,7 +224,61 @@ Install cmake: http://www.cmake.org/
 
 ## Building RISC-V target with cmake
 
-### Prerequisite: build risc-v clang toolchain and qemu
+### Native build on RISC-V SBC (e.g. SpacemiT K1/K3)
+
+On a 64-bit RISC-V system, CMake automatically detects `riscv64` and enables
+RVV with `-march=rv64gcv`:
+
+    cmake -B out/Release -DCMAKE_BUILD_TYPE=Release -DUNIT_TEST=ON
+    cmake --build out/Release
+
+To build for 32-bit RISC-V targets:
+
+    cmake -B out/Release -DCMAKE_BUILD_TYPE=Release -DRISCV_COMPILER_FLAGS="-march=rv32gcv"
+    cmake --build out/Release
+
+#### Customized Compiler Flags
+
+Customized compiler flags can be passed with `-DRISCV_COMPILER_FLAGS="xxx"`.
+When assigned, the specified flags are used instead of the default `-march=rv64gcv`:
+
+Targeting SiFive X280:
+
+    cmake -B out/Release -DUNIT_TEST=ON \
+          -DCMAKE_BUILD_TYPE=Release \
+          -DRISCV_COMPILER_FLAGS="-mcpu=sifive-x280"
+
+Targeting Coral (32-bit without floating point, Zve32x):
+
+    cmake -B out/Release -DUNIT_TEST=ON \
+          -DCMAKE_BUILD_TYPE=Release \
+          -DRISCV_COMPILER_FLAGS="-march=rv32imac_zve32x"
+
+To disable RVV:
+
+    cmake -B out/Release -DCMAKE_BUILD_TYPE=Release -DUSE_RVV=OFF
+
+### Building RISC-V with Bazel and Blaze
+
+To build with Bazel for 64-bit or 32-bit RISC-V targets:
+
+    bazel test --platforms=@platforms//cpu:riscv64 //...
+    bazel test --platforms=@platforms//cpu:riscv32 //...
+
+For custom targets such as SiFive X280 or Coral:
+
+    bazel test --platforms=@platforms//cpu:riscv64 --copt=-mcpu=sifive-x280 //...
+    bazel test --platforms=@platforms//cpu:riscv32 --copt=-march=rv32imac_zve32x //...
+
+In google3 using Blaze:
+
+    blaze test --config=mpu64 //third_party/libyuv:libyuv_test
+    blaze run --config=mpu64 //third_party/libyuv:cpuid
+    blaze run --config=mpu64 //third_party/libyuv:yuvconvert
+
+### Cross-compile for RISC-V target using QEMU
+
+#### Prerequisite: build risc-v clang toolchain and qemu
 
 If you don't have prebuilt clang and riscv64 qemu, run the script to download source and build them.
 
@@ -232,7 +286,7 @@ If you don't have prebuilt clang and riscv64 qemu, run the script to download so
 
 After running script, clang & qemu are built in `build-toolchain-qemu/riscv-clang/` & `build-toolchain-qemu/riscv-qemu/`.
 
-### Cross-compile for RISC-V target
+#### Cross-compile for RISC-V target
     cmake -B out/Release/ -DUNIT_TEST=ON \
           -DCMAKE_BUILD_TYPE=Release \
           -DCMAKE_TOOLCHAIN_FILE="./riscv_script/riscv-clang.cmake" \
@@ -240,19 +294,6 @@ After running script, clang & qemu are built in `build-toolchain-qemu/riscv-clan
           -DUSE_RVV=ON .
     cmake --build out/Release/
 
-#### Customized Compiler Flags
-
-Customized compiler flags are supported by `-DRISCV_COMPILER_FLAGS="xxx"`.
-If `-DRISCV_COMPILER_FLAGS="xxx"` is manually assigned, other compile flags(e.g disable -march=xxx) will not be appended.
-
-Example:
-
-    cmake -B out/Release/ -DUNIT_TEST=ON \
-          -DCMAKE_BUILD_TYPE=Release \
-          -DCMAKE_TOOLCHAIN_FILE="./riscv_script/riscv-clang.cmake" \
-          -DRISCV_COMPILER_FLAGS="-mcpu=sifive-x280" \
-          .
-
 ### Run on QEMU
 
 #### Run libyuv_unittest on QEMU