Index: test/CMakeLists.txt
===================================================================
--- test/CMakeLists.txt
+++ test/CMakeLists.txt
@@ -15,36 +15,40 @@
     string(REGEX REPLACE ".*ccache\ +" "" LLDB_TEST_COMPILER ${CMAKE_C_COMPILER} ${CMAKE_C_COMPILER_ARG1})
 endif()
 
-# Users can override LLDB_TEST_ARGS to modify the way LLDB tests are run. See help below.
-set(LLDB_TEST_ARGS
-  -C
-  ${LLDB_TEST_COMPILER}
-  CACHE STRING "Specify compiler(s) and architecture(s) with which run LLDB tests. For example: '-C gcc -C clang -A i386 -A x86_64'"
-  )
-string(REPLACE " " ";" LLDB_TEST_ARGS ${LLDB_TEST_ARGS})
-
-set(LLDB_TRACE_DIR "${CMAKE_BINARY_DIR}/lldb-test-traces"
-  CACHE STRING "Set directory to output LLDB test traces (for tests that do not pass.)"
-  )
-
-set(LLDB_COMMON_TEST_ARGS
+# The default architecture with which to compile test executables is the architecture that LLDB
+# itself was built with.
+string(TOLOWER "${LLVM_TARGET_ARCH}" LLDB_DEFAULT_TEST_ARCH)
+if( LLDB_DEFAULT_TEST_ARCH STREQUAL "host" )
+  string(REGEX MATCH "^[^-]*" LLDB_DEFAULT_TEST_ARCH ${LLVM_HOST_TRIPLE})
+endif ()
+
+# Allow the user to override the default by setting LLDB_TEST_ARCH
+set(LLDB_TEST_ARCH
+	${LLDB_DEFAULT_TEST_ARCH}
+	CACHED STRING "Specify the architecture to run LLDB tests as (x86|x64).  Determines whether tests are compiled with -m32 or -m64")
+
+# Users can override LLDB_TEST_USER_ARGS to specify arbitrary arguments to pass to the script
+set(LLDB_TEST_USER_ARGS
+  -C ${LLDB_TEST_COMPILER}
+  CACHE STRING "Specify additional arguments to pass to test runner. For example: '-C gcc -C clang -A i386 -A x86_64'")
+
+set(LLDB_TEST_COMMON_ARGS
+  --arch=${LLDB_TEST_ARCH}
   --executable
   ${CMAKE_BINARY_DIR}/bin/lldb${CMAKE_EXECUTABLE_SUFFIX}
   -s
-  ${LLDB_TRACE_DIR}
+  ${CMAKE_BINARY_DIR}/lldb-test-traces
   -u CXXFLAGS
   -u CFLAGS
   )
 
 add_python_test_target(check-lldb-single
   ${LLDB_SOURCE_DIR}/test/dotest.py
-  "${LLDB_COMMON_TEST_ARGS};${LLDB_TEST_ARGS}"
-  "Testing LLDB with args: ${LLDB_COMMON_TEST_ARGS};${LLDB_TEST_ARGS}"
+  "${LLDB_TEST_COMMON_ARGS};${LLDB_TEST_USER_ARGS}"
+  "Testing LLDB with args: ${LLDB_TEST_COMMON_ARGS};${LLDB_TEST_USER_ARGS}"
   )
 
-set(LLDB_DOSEP_ARGS
-  -o;\"-q;${LLDB_COMMON_TEST_ARGS};${LLDB_TEST_ARGS}\"
-  )
+set(LLDB_DOSEP_ARGS -o;\"-q;${LLDB_TEST_COMMON_ARGS};${LLDB_TEST_USER_ARGS}\")
 
 # If tests crash cause LLDB to crash, or things are otherwise unstable, or if machine-parsable
 # output is desired (i.e. in continuous integration contexts) check-lldb-sep is a better target.
Index: test/dotest.py
===================================================================
--- test/dotest.py
+++ test/dotest.py
@@ -578,10 +578,7 @@
             if arch.startswith('arm') and platform_system == 'Darwin':
                 os.environ['SDKROOT'] = commands.getoutput('xcodebuild -version -sdk iphoneos.internal Path')
     else:
-        if (platform_system == 'Darwin' or (platform_system == 'Linux' and compilers == ['clang'])) and platform_machine == 'x86_64':
-            archs = ['x86_64', 'i386']
-        else:
-            archs = [platform_machine]
+        archs = [platform_machine]
 
     if args.categoriesList:
         categoriesList = set(validate_categories(args.categoriesList))
Index: test/make/Makefile.rules
===================================================================
--- test/make/Makefile.rules
+++ test/make/Makefile.rules
@@ -73,15 +73,22 @@
 	# On non-Apple platforms, -arch becomes -m
 	ARCHFLAG := -m
 
-	# i386 becomes 32, and amd64 or x86_64 becomes 64
+	# i386,i686 -> 32
+	# amd64, x86_64, x64 -> 64
 	ifeq "$(ARCH)" "amd64"
-	    override ARCH := $(subst amd64,64,$(ARCH))
+		override ARCH := $(subst amd64,64,$(ARCH))
 	endif
 	ifeq "$(ARCH)" "x86_64"
-	    override ARCH := $(subst x86_64,64,$(ARCH))
+		override ARCH := $(subst x86_64,64,$(ARCH))
+	endif
+	ifeq "$(ARCH)" "x64"
+		override ARCH := $(subst x64,64,$(ARCH))
 	endif
 	ifeq "$(ARCH)" "i386"
-	    override ARCH := $(subst i386,32,$(ARCH))
+		override ARCH := $(subst i386,32,$(ARCH))
+	endif
+	ifeq "$(ARCH)" "i686"
+		override ARCH := $(subst i686,32,$(ARCH))
 	endif
 
 	ifeq "$(SPLIT_DEBUG_SYMBOLS)" "YES"