From 08e0023b3dc5aeb5c7173cb456c24398d93dd815 Mon Sep 17 00:00:00 2001
From: Radek Doulik <radek.doulik@gmail.com>
Date: Wed, 10 Nov 2021 19:19:35 +0100
Subject: [PATCH] [release/6.0][wasm] Change dotnet.wasm link optimization
 (#60632)

* [wasm] Change dotnet.wasm link optimization

Context: https://github.com/dotnet/runtime/issues/60349

When we switched to Emscripten 2.0.21, we stopped using deprecated
`--llvm-opts 2` option. This caused unwanted performance degradation.
Switching to `-O2` get us similar performance as with `--llvm-opts`.

Blazor wasm test app `Time to first UI` benchmark times:

    branch/commit        link option    time    dotnet.wasm size
    --------------------+------------+--------+-----------------
    release/6.0 92ff02       -Oz       491ms    2,430,639
    release/6.0 92ff02       -O2       457ms    2,474,518
    release/6.0 92ff02       -O3       444ms    2,555,824

* Fix native build too

Co-authored-by: Larry Ewing <lewing@microsoft.com>
---
 src/mono/wasm/Makefile                     | 2 +-
 src/mono/wasm/build/WasmApp.Native.targets | 1 +
 src/mono/wasm/wasm.proj                    | 2 +-
 3 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/mono/wasm/Makefile b/src/mono/wasm/Makefile
index 52e5de9e302..63e03b22546 100644
--- a/src/mono/wasm/Makefile
+++ b/src/mono/wasm/Makefile
@@ -72,7 +72,7 @@ MONO_LIBS = \
 	$(ICU_LIBDIR)/libicui18n.a
 
 EMCC_DEBUG_FLAGS =-g -Os -s -DDEBUG=1
-EMCC_RELEASE_FLAGS=-Oz
+EMCC_RELEASE_FLAGS=-O2
 
 ifeq ($(NOSTRIP),)
 STRIP_CMD=&& $(EMSDK_PATH)/upstream/bin/wasm-opt --strip-dwarf $(NATIVE_BIN_DIR)/dotnet.wasm -o $(NATIVE_BIN_DIR)/dotnet.wasm
diff --git a/src/mono/wasm/build/WasmApp.Native.targets b/src/mono/wasm/build/WasmApp.Native.targets
index e564d43520b..22538f7ee77 100644
--- a/src/mono/wasm/build/WasmApp.Native.targets
+++ b/src/mono/wasm/build/WasmApp.Native.targets
@@ -161,6 +161,7 @@
       <_EmccOptimizationFlagDefault Condition="'$(_EmccOptimizationFlagDefault)' == ''">-Oz</_EmccOptimizationFlagDefault>
 
       <EmccCompileOptimizationFlag Condition="'$(EmccCompileOptimizationFlag)' == ''">$(_EmccOptimizationFlagDefault)</EmccCompileOptimizationFlag>
+      <EmccLinkOptimizationFlag    Condition="'$(EmccLinkOptimizationFlag)' == '' and '$(Configuration)' == 'Release'">-O2</EmccLinkOptimizationFlag>
       <EmccLinkOptimizationFlag    Condition="'$(EmccLinkOptimizationFlag)' == ''"   >$(EmccCompileOptimizationFlag)</EmccLinkOptimizationFlag>
 
       <_EmccCompileRsp>$(_WasmIntermediateOutputPath)emcc-compile.rsp</_EmccCompileRsp>
diff --git a/src/mono/wasm/wasm.proj b/src/mono/wasm/wasm.proj
index 3eacc3e1307..1051ff672f9 100644
--- a/src/mono/wasm/wasm.proj
+++ b/src/mono/wasm/wasm.proj
@@ -180,7 +180,7 @@
 
     <PropertyGroup>
       <EmccConfigurationFlags Condition="'$(Configuration)' == 'Debug'">-g -Os -s -DENABLE_NETCORE=1 -DDEBUG=1</EmccConfigurationFlags>
-      <EmccConfigurationFlags Condition="'$(Configuration)' == 'Release'">-Oz -DENABLE_NETCORE=1</EmccConfigurationFlags>
+      <EmccConfigurationFlags Condition="'$(Configuration)' == 'Release'">-O2 -DENABLE_NETCORE=1</EmccConfigurationFlags>
       <StripCmd>&quot;$(EMSDK_PATH)/upstream/bin/wasm-opt&quot; --strip-dwarf &quot;$(NativeBinDir)dotnet.wasm&quot; -o &quot;$(NativeBinDir)dotnet.wasm&quot;</StripCmd>
       <WasmObjDir>$(ArtifactsObjDir)wasm</WasmObjDir>
       <WasmVersionFile>$(WasmObjDir)\emcc-version.txt</WasmVersionFile>
-- 
2.34.1