Use Oz and flto flags to reduce Emscripten shared library size to 44/45 Mb

Author: mcbarton

.github/workflows/emscripten.yml

@@ -195,7 +195,7 @@ jobs:
                         -DCLANG_BUILD_TOOLS=OFF                         \
                         -DLLVM_NATIVE_TOOL_DIR=$NATIVE_DIR 		\
                          ../llvm
-          emmake ninja clang cling lld gtest_main
+          EMCC_CFLAGS="-Oz -flto" emmake ninja clang cling lld gtest_main
         else
           # Apply patches
           llvm_vers=$(echo "${{ matrix.clang-runtime }}" | tr '[:lower:]' '[:upper:]')
@@ -226,7 +226,7 @@ jobs:
                         -G Ninja                                         \
                         -DLLVM_NATIVE_TOOL_DIR=$NATIVE_DIR 		\
                         ../llvm
-          emmake ninja libclang clangInterpreter clangStaticAnalyzerCore lldWasm
+          EMCC_CFLAGS="-Oz -flto" emmake ninja libclang clangInterpreter clangStaticAnalyzerCore lldWasm
         fi
         cd ../
         rm -rf $(find . -maxdepth 1 ! -name "build" ! -name "llvm" ! -name "clang" ! -name ".")
@@ -296,6 +296,7 @@ jobs:
                         -DLLVM_ENABLE_LIBPFM=OFF                        `
                         -DCLANG_BUILD_TOOLS=OFF                         `
                 ..\llvm
+          $env:EMCC_CFLAGS="-Oz -flto"
           emmake make clang cling lld gtest_main
         }
         else
@@ -337,6 +338,7 @@ jobs:
                         -DCLANG_BUILD_TOOLS=OFF                         `
                         -G Ninja `
                         ..\llvm
+          $env:EMCC_CFLAGS="-Oz -flto"
           emmake ninja libclang clangInterpreter clangStaticAnalyzerCore lldWasm
         }
         cd ..\

Emscripten-build-instructions.md

@@ -100,9 +100,9 @@ emcmake cmake -DCMAKE_BUILD_TYPE=Release \
                         -DCLANG_BUILD_TOOLS=OFF                         \
                         -DLLVM_NATIVE_TOOL_DIR=$NATIVE_DIR              \
                         ../llvm
-emmake make libclang -j $(nproc --all)
-emmake make clangInterpreter clangStaticAnalyzerCore -j $(nproc --all)
-emmake make lldWasm -j $(nproc --all)
+EMCC_CFLAGS="-Oz -flto" emmake make libclang -j $(nproc --all)
+EMCC_CFLAGS="-Oz -flto" emmake make clangInterpreter clangStaticAnalyzerCore -j $(nproc --all)
+EMCC_CFLAGS="-Oz -flto" emmake make lldWasm -j $(nproc --all)
 ```
 
 or executing
@@ -131,7 +131,9 @@ emcmake cmake -DCMAKE_BUILD_TYPE=Release `
                         -DCLANG_BUILD_TOOLS=OFF                         `
                         -G Ninja `
                         ..\llvm
+$env:EMCC_CFLAGS="-Oz -flto"
 emmake ninja libclang clangInterpreter clangStaticAnalyzerCore lldWasm
+$env:EMCC_CFLAGS=""
 ```
 
 on Windows. Once this finishes building we need to take note of where we built our llvm build. This can be done by executing the following on Linux and osx

docs/Emscripten-build-instructions.rst

@@ -120,9 +120,9 @@ and osx
                  -DCLANG_BUILD_TOOLS=OFF                         \
                  -DLLVM_NATIVE_TOOL_DIR=$NATIVE_DIR 		\
                  ../llvm
-   emmake make libclang -j $(nproc --all)
-   emmake make clangInterpreter clangStaticAnalyzerCore -j $(nproc --all)
-   emmake make lldWasm -j $(nproc --all)
+   EMCC_CFLAGS="-Oz -flto" emmake make libclang -j $(nproc --all)
+   EMCC_CFLAGS="-Oz -flto" emmake make clangInterpreter clangStaticAnalyzerCore -j $(nproc --all)
+   EMCC_CFLAGS="-Oz -flto" emmake make lldWasm -j $(nproc --all)
 
 or executing
 
@@ -151,7 +151,9 @@ or executing
                         -DCLANG_BUILD_TOOLS=OFF                         `
                         -G Ninja `
                         ..\llvm
+   $env:EMCC_CFLAGS="-Oz -flto" 
    emmake ninja libclang clangInterpreter clangStaticAnalyzerCore lldWasm
+   $env:EMCC_CFLAGS=""
 
 on Windows. Once this finishes building we need to take note of where we built our llvm build.
 This can be done by executing the following on Linux and osx

lib/CppInterOp/CMakeLists.txt

@@ -127,10 +127,16 @@ if(EMSCRIPTEN)
   set_target_properties(clangCppInterOp
     PROPERTIES NO_SONAME 1
   )
+  target_compile_options(clangCppInterOp
+    PRIVATE "SHELL: -Oz"
+    PRIVATE "SHELL: -flto"
+  )
   target_link_options(clangCppInterOp
     PRIVATE "SHELL: -s WASM_BIGINT"
     PRIVATE "SHELL: -s SIDE_MODULE=1"
     PRIVATE "SHELL: ${SYMBOLS_LIST}"
+    PRIVATE "SHELL: -Oz"
+    PRIVATE "SHELL: -flto"
   )
 else()
   target_link_options(clangCppInterOp

lib/CppInterOp/exports.ld

@@ -50,4 +50,5 @@
 -Wl,--export=_ZNK5clang4Type14isFloatingTypeEv
 -Wl,--export=_ZNK5clang12FunctionDecl12getNumParamsEv
 -Wl,--export=__clang_Interpreter_SetValueNoAlloc
--Wl,--export=__clang_Interpreter_SetValueWithAlloc
+-Wl,--export=__clang_Interpreter_SetValueWithAlloc
+-Wl,--export=_ZN4llvm15SmallVectorBaseIjE8set_sizeEm