[CMake] Ignore arm_*.h for non-ARM build

[sunlin]

Summary

Copy the arm_*.h files only "ARM" is in build targets.

[kristof.beyls]

I'm wondering what the rationale for this change is.
If there is a good rationale for this; wouldn't it need to be applied to all target-specific header files, not only the Arm-specific header files?

[sunlin]

Hi @kristof.beyls The original lib/clang/12.0.1/include is about total ~10M, and the arm*.h take about ~5M. Ignore these unused header files will save the developers who work on the low storage device.

[kristof.beyls]

In D103080#2790139, @sunlin wrote:

Hi @kristof.beyls The original lib/clang/12.0.1/include is about total ~10M, and the arm*.h take about ~5M. Ignore these unused header files will save the developers who work on the low storage device.

Thanks for sharing that rationale!
I have two immediate thoughts on this patch:

• arm_neon.h and other header files need to be kept also for the AArch64 backend. As is, I think the patch will remove them resulting in a broken toolchain if the AArch64 backend is requested but the Arm backend is not.
• We should implement either (a) remove all target-specific header files if a target is not built or (b) keep all of them. Selecting ad hoc (e.g. applying this design principle only for the Arm backend) which ones to apply this policy to doesn't seem like a good design to me.

[chill]

IMHO, it's possible to write a frontend test, which includes, say arm_neon.h, but does not really require the ARM or AArch64 backends to be configured (e.g. CodeGen/arm-vector-align.c?)
If arm_neon.h is not built, then the test would need the appropriate REQUIRES line, but than that means the frontend test coverage would decrease for people, who
are not interested in Arm backends. Mind you, even if a test is Arm specific, that does not mean it does not depend on generic code.

[efriedma]

I think I'm fine with the general direction, but it would be nice to have a CMake option to force the headers for all targets to be built if someone needs them. For static analysis or something like that, I can imagine someone building LLVM without any backends at all.

[sunlin]

Yes, a CMake option is a good idea for this.
I'll update this change to add a new CMake option for who don't want all the headers (default OFF to follow exist behavior) .

[sunlin]

Close it for ignore these headers from command line.

It is included from chain: "include/clang/Basic/TargetBuiltins.h" --> "clang/Basic/BuiltinsARM.def" --> "include/clang/Basic/arm_cde_builtins.inc"...

clang/lib/Headers/CMakeLists.txt

 set(files
   adxintrin.h
   altivec.h
   ammintrin.h
   amxintrin.h
-  arm_acle.h
-  arm_cmse.h
-  armintr.h
-  arm64intr.h
   avx2intrin.h
   avx512bf16intrin.h
   avx512bwintrin.h
   avx512bitalgintrin.h
   avx512vlbitalgintrin.h
   avx512cdintrin.h
   avx512vpopcntdqintrin.h
   avx512dqintrin.h
set(files
   xopintrin.h
   xsavecintrin.h
   xsaveintrin.h
   xsaveoptintrin.h
   xsavesintrin.h
   xtestintrin.h
   )
 
+if ("ARM" IN_LIST LLVM_TARGETS_TO_BUILD)
+  set(files ${files}
+  arm_acle.h
+  arm_cmse.h
+  armintr.h
+  arm64intr.h
+  )
+endif()
+
 set(cuda_wrapper_files
   cuda_wrappers/algorithm
   cuda_wrappers/complex
   cuda_wrappers/new
 )
 
 set(ppc_wrapper_files
   ppc_wrappers/mmintrin.h

 endfunction(clang_generate_header)
 
 
 # Copy header files from the source directory to the build directory
 foreach( f ${files} ${cuda_wrapper_files} ${ppc_wrapper_files} ${openmp_wrapper_files})
   copy_header_to_output_dir(${CMAKE_CURRENT_SOURCE_DIR} ${f})
 endforeach( f )
 
+if ("ARM" IN_LIST LLVM_TARGETS_TO_BUILD)
   # Generate header files and copy them to the build directory
   # Generate arm_neon.h
   clang_generate_header(-gen-arm-neon arm_neon.td arm_neon.h)
   # Generate arm_fp16.h
   clang_generate_header(-gen-arm-fp16 arm_fp16.td arm_fp16.h)
   # Generate arm_sve.h
   clang_generate_header(-gen-arm-sve-header arm_sve.td arm_sve.h)
   # Generate arm_bf16.h
   clang_generate_header(-gen-arm-bf16 arm_bf16.td arm_bf16.h)
   # Generate arm_mve.h
   clang_generate_header(-gen-arm-mve-header arm_mve.td arm_mve.h)
   # Generate arm_cde.h
   clang_generate_header(-gen-arm-cde-header arm_cde.td arm_cde.h)
+endif()
 # Generate riscv_vector.h
 clang_generate_header(-gen-riscv-vector-header riscv_vector.td riscv_vector.h)
 
 add_custom_target(clang-resource-headers ALL DEPENDS ${out_files})
 set_target_properties(clang-resource-headers PROPERTIES
   FOLDER "Misc"
   RUNTIME_OUTPUT_DIRECTORY "${output_dir}")