[compiler-rt] Update compiler-rt for cross-compilation with multiple architectures

[fjricci]

Summary

This allows for building compiler-rt to target multiple android
architectures, by using a set of -DTARGET_<arch>_CFLAGS cmake arguments.

[compnerd]

The various architecture spellings are available in config-ix.cmake, and it seems nicer to re-use those. Note that the alternate that I proposed I just wrote up, didnt actually run, so it probably requires tweaking :-)

cmake/Modules/CompilerRTUtils.cmake

147

I think that this is better written as:

set(SAVED_CMAKE_REQUIRED_FLAS "${CMAKE_REQUIRED_FLAGS}")
foreach(arch ARM64;ARM32;X86;X86_64;MIPS32;MIPS64;S390X;WASM32;WASM64)
  set(CMAKE_REQUIRED_FLAGS "${SAVED_CMAKE_REQUIRED_FLAGS} ${${TARGET_${arch}_CFLAGS}}")
  foreach(spelling ${${arch}})
    check_symbol_exists(__${spelling}__ "" __${arch}_${spelling})
    if(__${arch}_${spelling})
      add_default_target_arch("${arch}")
      break()
    endif()
  endforeach()
endforeach()

[fjricci]

Multiple simultaneous architectures are not well-supported by cmake (for example, checks for existing headers only occur once).

[beanz]

In general we need to be moving compiler-rt into the direction of building one and only one architecture per CMake invocation except on platforms that support fat binaries, where we should support one target platform per invocation.

There is a lot of work to be done to get to that point, but it is the way to go so that we stop fighting with CMake trying to make it do things it isn't designed to do.

-Chris

cmake/Modules/CompilerRTUtils.cmake

macro(test_target_arch arch def)
   elseif("${COMPILER_RT_DEFAULT_TARGET_ARCH}" MATCHES "${arch}" AND
          COMPILER_RT_HAS_EXPLICIT_DEFAULT_TARGET_TRIPLE)
     # Bail out if we cannot target the architecture we plan to test.
     message(FATAL_ERROR "Cannot compile for ${arch}:\n${TARGET_${arch}_OUTPUT}")
   endif()
 endmacro()
 
 macro(detect_target_arch)
-  check_symbol_exists(__arm__ "" __ARM)
-  check_symbol_exists(__aarch64__ "" __AARCH64)
-  check_symbol_exists(__x86_64__ "" __X86_64)
-  check_symbol_exists(__i686__ "" __I686)
-  check_symbol_exists(__i386__ "" __I386)
-  check_symbol_exists(__mips__ "" __MIPS)
-  check_symbol_exists(__mips64__ "" __MIPS64)
-  check_symbol_exists(__s390x__ "" __S390X)
-  check_symbol_exists(__wasm32__ "" __WEBASSEMBLY32)
-  check_symbol_exists(__wasm64__ "" __WEBASSEMBLY64)
-  if(__ARM)
-    add_default_target_arch(arm)
-  elseif(__AARCH64)
-    add_default_target_arch(aarch64)
-  elseif(__X86_64)
-    add_default_target_arch(x86_64)
-  elseif(__I686)
-    add_default_target_arch(i686)
-  elseif(__I386)
-    add_default_target_arch(i386)
-  elseif(__MIPS64) # must be checked before __MIPS
-    add_default_target_arch(mips64)
-  elseif(__MIPS)
-    add_default_target_arch(mips)
-  elseif(__S390X)
-    add_default_target_arch(s390x)
-  elseif(__WEBASSEMBLY32)
-    add_default_target_arch(wasm32)
-  elseif(__WEBASSEMBLY64)
-    add_default_target_arch(wasm64)
+  set(SAVED_CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")
+  foreach(arch arm;aarch64;x86_64;i686;mips;mips64;s390x;wasm32;wasm64)
+    string(TOUPPER ${arch} arch_upper)
+    set(TARGET_CFLAGS "${TARGET_${arch_upper}_CFLAGS}")
+    set(CMAKE_REQUIRED_FLAGS "${SAVED_CMAKE_REQUIRED_FLAGS} ${TARGET_CFLAGS}")
+    check_symbol_exists(__${arch}__ "" __${arch_upper})
+    if(__${arch_upper})
+      add_default_target_arch("${arch}")
     endif()
+  endforeach()
+  set(CMAKE_REQUIRED_FLAGS "${SAVED_CMAKE_REQUIRED_FLAGS}")
 endmacro()

lib/builtins/CMakeLists.txt

if (CAN_TARGET_${arch})
       foreach (_file ${${arch}_SOURCES})
         if (${_file} MATCHES ${arch}/*)
           get_filename_component(_name ${_file} NAME)
           string(REPLACE ".S" ".c" _cname "${_name}")
           list(REMOVE_ITEM ${arch}_SOURCES ${_cname})
         endif ()
       endforeach ()
 
+      string(TOUPPER ${arch} arch_upper)
+      set(TARGET_CFLAGS "${TARGET_${arch_upper}_CFLAGS}")
       add_compiler_rt_runtime(clang_rt.builtins
                               STATIC
                               ARCHS ${arch}
                               SOURCES ${${arch}_SOURCES}
-                              CFLAGS ${maybe_stdc99}
+                              CFLAGS ${maybe_stdc99} ${TARGET_CFLAGS}
                               PARENT_TARGET builtins)
     endif ()
   endforeach ()
 endif ()
 
 add_dependencies(compiler-rt builtins)