How to enable AVX or SSE optimizations while building UE4 project?

Development Platform & Builds Debugging, Optimization, & Profiling
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1

I have a library which uses AVX and SSE optimizations, to enable these it expects " /arch:AVX " flag to be passed to Visual C++ compiler.
I do not see any option to set compiler flags in UE4 project. Is there any way to do this?

Thanks

2

Engine\Source\Programs\UnrealBuildTool\Windows\VCToolChain.cs

//
			//	PC
			//
			if ((CompileEnvironment.Config.Target.Platform == CPPTargetPlatform.Win32) || 
				(CompileEnvironment.Config.Target.Platform == CPPTargetPlatform.Win64))
			{
				// SSE options are not allowed when using CLR compilation
				if (CompileEnvironment.Config.CLRMode == CPPCLRMode.CLRDisabled && WindowsPlatform.bUseVCCompilerArgs)
				{
					if (CompileEnvironment.Config.bUseAVX)
					{
						// Allow the compiler to generate AVX instructions.
						Arguments.Append(" /arch:AVX");
					}
					// SSE options are not allowed when using the 64 bit toolchain
					// (enables SSE2 automatically)
					else if (CompileEnvironment.Config.Target.Platform != CPPTargetPlatform.Win64)
					{
						// Allow the compiler to generate SSE2 instructions.
						Arguments.Append(" /arch:SSE2");
					}
				}

As you see, you have to provide somehow bUseAVX flag, I believe this may be done in:

public override void SetupGlobalEnvironment(
        TargetInfo Target,
        ref LinkEnvironmentConfiguration OutLinkEnvironmentConfiguration,
        ref CPPEnvironmentConfiguration OutCPPEnvironmentConfiguration
        )
    {
    }

in your project TargetRules. For example take a look at Engine\Source\UE4Game.Target.cs

3

Hi ,
Sorry for the late reply.

Is there a way to do this without modifying / compiling the engine from source ?

The tried override of SetupGlobalEnvironment in MyGame.Target.cs and MyGameEditor.Target.cs, but it was not called.

4

Use in your project TargetRules.

 public override void SetupGlobalEnvironment(
         TargetInfo Target,
         ref LinkEnvironmentConfiguration OutLinkEnvironmentConfiguration,
         ref CPPEnvironmentConfiguration OutCPPEnvironmentConfiguration
         )
     {
OutCPPEnvironmentConfiguration.bUseAVX = true;
     }