Check for the right spelling of the implicit-it option

Author: statham-arm

compiler-rt/cmake/Modules/CheckAssemblerFlag.cmake

@@ -0,0 +1,38 @@
+# Helper function to find out whether the assembler supports a particular
+# command-line flag. You'd like to use the standard check_compiler_flag(), but
+# that only supports a fixed list of languages, and ASM isn't one of them. So
+# we do it ourselves, by trying to assemble an empty source file.
+
+function(check_assembler_flag outvar flag)
+  if(NOT DEFINED "${outvar}")
+    if(NOT CMAKE_REQUIRED_QUIET)
+      message(CHECK_START "Checking for assembler flag ${flag}")
+    endif()
+
+    # Stop try_compile from attempting to link the result of the assembly, so
+    # that we don't depend on having a working linker, and also don't have to
+    # figure out what special symbol like _start needs to be defined in the
+    # test input.
+    #
+    # This change is made within the dynamic scope of this function, so
+    # CMAKE_TRY_COMPILE_TARGET_TYPE will be restored to its previous value on
+    # return.
+    set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
+
+    # Try to assemble an empty file with a .S name, using the provided flag.
+    try_compile(success
+      SOURCE_FROM_CONTENT "CheckAssemblerFlag.s" ""
+      COMPILE_DEFINITIONS ${flag}
+      NO_CACHE)
+
+    if(NOT CMAKE_REQUIRED_QUIET)
+      if(success)
+        message(CHECK_PASS "Accepted")
+        set(${outvar} 1 CACHE INTERNAL "Test assembler flag ${flag}")
+      else()
+        message(CHECK_FAIL "Not accepted")
+        set(${outvar} "" CACHE INTERNAL "Test assembler flag ${flag}")
+      endif()
+    endif()
+  endif()
+endfunction()

compiler-rt/lib/builtins/CMakeLists.txt

@@ -60,6 +60,7 @@ endif()
 include(builtin-config-ix)
 include(CMakeDependentOption)
 include(CMakePushCheckState)
+include(CheckAssemblerFlag)
 
 option(COMPILER_RT_BUILTINS_HIDE_SYMBOLS
   "Do not export any symbols from the static library." ON)
@@ -426,11 +427,24 @@ option(COMPILER_RT_ARM_OPTIMIZED_FP
   "On 32-bit Arm, use optimized assembly implementations of FP arithmetic. Likely to increase code size, but be faster." ON)
 
 if(COMPILER_RT_ARM_OPTIMIZED_FP)
+  check_assembler_flag(COMPILER_RT_HAS_MIMPLICIT_IT -mimplicit-it=always)
+  if(COMPILER_RT_HAS_MIMPLICIT_IT)
+    set(implicit_it_flag -mimplicit-it=always)
+  else()
+    check_assembler_flag(
+      COMPILER_RT_HAS_WA_MIMPLICIT_IT -Wa,-mimplicit-it=always)
+    if(COMPILER_RT_HAS_WA_MIMPLICIT_IT)
+      set(implicit_it_flag -Wa,-mimplicit-it=always)
+    else()
+      message(FATAL_ERROR "Don't know how to set the -mimplicit-it=always flag in this assembler")
+    endif()
+  endif()
+
   set(assembly_files
     arm/mulsf3.S
     arm/divsf3.S)
   set_source_files_properties(${assembly_files}
-    PROPERTIES COMPILE_OPTIONS "-Wa,-mimplicit-it=always")
+    PROPERTIES COMPILE_OPTIONS ${implicit_it_flag})
   set(arm_or_thumb2_base_SOURCES
     ${assembly_files}
     arm/fnan2.c