[Buildroot] [RFC PATCH v4 5/9] llvm: add config to build backend for host arch

[Thomas Petazzoni]

Hello,

On Thu, 14 Jun 2018 15:48:16 -0700, Joseph Kogut wrote:
> Signed-off-by: Joseph Kogut <joseph.kogut at gmail.com>
> ---
>  package/llvm/Config.in | 11 +++++++++++
>  package/llvm/llvm.mk   |  9 ++++++++-
>  2 files changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/package/llvm/Config.in b/package/llvm/Config.in
> index 83e94660eb..dd07b23e07 100644
> --- a/package/llvm/Config.in
> +++ b/package/llvm/Config.in
> @@ -11,6 +11,12 @@ config BR2_PACKAGE_LLVM_TARGET_ARCH
>  	default "ARM" if BR2_arm || BR2_armeb
>  	default "X86" if BR2_i386 || BR2_x86_64
>  
> +config BR2_PACKAGE_LLVM_HOST_ARCH
> +	string
> +	default "AArch64" if BR2_HOSTARCH="aarch64"
> +	default "X86" if BR2_HOSTARCH = "x86" || BR2_HOSTARCH = "x86_64"
> +	default "ARM" if BR2_HOSTARCH = "arm"
> +
>  config BR2_PACKAGE_LLVM
>  	bool "llvm"
>  	depends on BR2_PACKAGE_LLVM_ARCH_SUPPORTS
> @@ -27,6 +33,11 @@ config BR2_PACKAGE_LLVM
>  
>  	  http://llvm.org
>  
> +config BR2_PACKAGE_LLVM_ENABLE_HOST_ARCH
> +	bool "Build backend for host architecture"
> +	help
> +	  Build code generator for host machine.

So I'm going to disagree a bit with Valentin on this one. If I
understand correctly, this option is going to change what host-llvm
builds, not what the target llvm package builds. So it is a host
package option, and as such is more logically named
BR2_PACKAGE_HOST_LLVM_<something>.

*But* they should be moved to a new package/llvm/Config.in.host file,
and BR2_PACKAGE_HOST_LLVM_ENABLE_HOST_ARCH should be made a blind
option (i.e without prompt). This blind option will be selected by
whichever package needs host architecture support in host-llvm.

> diff --git a/package/llvm/llvm.mk b/package/llvm/llvm.mk
> index 3abf428989..50cc74d299 100644
> --- a/package/llvm/llvm.mk
> +++ b/package/llvm/llvm.mk
> @@ -39,8 +39,9 @@ LLVM_CONF_OPTS += -DLLVM_BUILD_GLOBAL_ISEL=OFF
>  LLVM_TARGET_ARCH = $(call qstrip,$(BR2_PACKAGE_LLVM_TARGET_ARCH))
>  
>  # Build backend for target architecture. This include backends like AMDGPU.
> +HOST_LLVM_TARGETS_TO_BUILD = $(LLVM_TARGET_ARCH)
>  LLVM_TARGETS_TO_BUILD = $(LLVM_TARGET_ARCH)
> -HOST_LLVM_CONF_OPTS += -DLLVM_TARGETS_TO_BUILD="$(subst $(space),;,$(LLVM_TARGETS_TO_BUILD))"
> +HOST_LLVM_CONF_OPTS += -DLLVM_TARGETS_TO_BUILD="$(subst $(space),;,$(HOST_LLVM_TARGETS_TO_BUILD))"
>  LLVM_CONF_OPTS += -DLLVM_TARGETS_TO_BUILD="$(subst $(space),;,$(LLVM_TARGETS_TO_BUILD))"
>  
>  # LLVM target to use for native code generation. This is required for JIT generation.
> @@ -56,9 +57,15 @@ LLVM_CONF_OPTS += -DLLVM_TARGET_ARCH=$(LLVM_TARGET_ARCH)
>  # output only $(LLVM_TARGET_ARCH) if not, and mesa3d won't build as
>  # it thinks AMDGPU backend is not installed on the target.
>  ifeq ($(BR2_PACKAGE_LLVM_AMDGPU),y)
> +HOST_LLVM_TARGETS_TO_BUILD += AMDGPU
>  LLVM_TARGETS_TO_BUILD += AMDGPU
>  endif
>  
> +# Build backend for host architecture
> +ifeq ($(BR2_PACKAGE_LLVM_ENABLE_HOST_ARCH),y)
> +HOST_LLVM_TARGETS_TO_BUILD += $(call qstrip,$(BR2_PACKAGE_LLVM_HOST_ARCH))
> +endif

I think this could be improved. Something like this:

LLVM_TARGETS_TO_BUILD = $(LLVM_TARGET_ARCH)

ifeq ($(BR2_PACKAGE_LLVM_AMDGPU),y)
LLVM_TARGETS_TO_BUILD += AMDGPU
endif

 ... potentially more additions to LLVM_TARGETS_TO_BUILD here ...

LLVM_CONF_OPTS += -DLLVM_TARGETS_TO_BUILD="$(subst $(space),;,$(LLVM_TARGETS_TO_BUILD))"

# host-llvm at least needs to build the same targets as the ones needed
# by the target llvm
HOST_LLVM_TARGETS_TO_BUILD = $(LLVM_TARGETS_TO_BUILD)

ifeq ($(BR2_PACKAGE_HOST_LLVM_ENABLE_HOST_ARCH),y)
HOST_LLVM_TARGETS_TO_BUILD += $(call qstrip,$(BR2_PACKAGE_LLVM_HOST_ARCH))
endif

HOST_LLVM_CONF_OPTS += -DLLVM_TARGETS_TO_BUILD="$(subst $(space),;,$(HOST_LLVM_TARGETS_TO_BUILD))"

And there you go.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com