Index: llvm/cmake/modules/AddLLVM.cmake
===================================================================
--- llvm/cmake/modules/AddLLVM.cmake
+++ llvm/cmake/modules/AddLLVM.cmake
@@ -1113,6 +1113,8 @@
 # common variables that any Lit instance is likely to need, and custom
 # variables can be passed in.
 function(configure_lit_site_cfg input output)
+  cmake_parse_arguments(ARG "ALL" "" "OUTPUT_MAPPING" ${ARGN})
+
   foreach(c ${LLVM_TARGETS_TO_BUILD})
     set(TARGETS_BUILT "${TARGETS_BUILT} ${c}")
   endforeach(c)
@@ -1180,7 +1182,10 @@
   configure_file(${input} ${output} @ONLY)
   get_filename_component(INPUT_DIR ${input} DIRECTORY)
   if (EXISTS "${INPUT_DIR}/lit.cfg")
-    set(PYTHON_STATEMENT "map_config('${INPUT_DIR}/lit.cfg', '${output}')")
+    if ("${ARG_OUTPUT_MAPPING}" STREQUAL "")
+      set(ARG_OUTPUT_MAPPING "${output}")
+    endif()
+    set(PYTHON_STATEMENT "map_config('${INPUT_DIR}/lit.cfg', '${ARG_OUTPUT_MAPPING}')")
     get_property(LLVM_LIT_CONFIG_MAP GLOBAL PROPERTY LLVM_LIT_CONFIG_MAP)
     set(LLVM_LIT_CONFIG_MAP "${LLVM_LIT_CONFIG_MAP}\n${PYTHON_STATEMENT}")
     set_property(GLOBAL PROPERTY LLVM_LIT_CONFIG_MAP ${LLVM_LIT_CONFIG_MAP})
Index: llvm/utils/lit/CMakeLists.txt
===================================================================
--- llvm/utils/lit/CMakeLists.txt
+++ llvm/utils/lit/CMakeLists.txt
@@ -1,7 +1,12 @@
 # The configured file is not placed in the correct location
 # until the tests are run as we need to copy it into
 # a copy of the tests folder
-configure_lit_site_cfg("tests/lit.site.cfg.in" "lit.site.cfg")
+configure_lit_site_cfg(
+  "${CMAKE_CURRENT_SOURCE_DIR}/tests/lit.site.cfg.in"
+  "${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg"
+  OUTPUT_MAPPING
+  "${CMAKE_CURRENT_BINARY_DIR}/tests/lit.site.cfg"
+  )
 
 # Lit's test suite creates output files next to the sources which makes the
 # source tree dirty. This is undesirable because we do out of source builds.
Index: llvm/utils/lit/lit/util.py
===================================================================
--- llvm/utils/lit/lit/util.py
+++ llvm/utils/lit/lit/util.py
@@ -9,6 +9,12 @@
 import sys
 import threading
 
+def norm_path(path):
+    path = os.path.realpath(path)
+    path = os.path.normpath(path)
+    path = os.path.normcase(path)
+    return path
+
 def is_string(value):
     try:
         # Python 2 and Python 3 are different here.
Index: llvm/utils/lit/tests/Inputs/config-map-discovery/driver.py
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/config-map-discovery/driver.py
@@ -0,0 +1,14 @@
+import lit.util
+import os
+import sys
+
+main_config = sys.argv[1]
+
+config_map = {lit.util.norm_path(main_config) : sys.argv[2]}
+builtin_parameters = {'config_map' : config_map}
+
+if __name__=='__main__':
+    from lit.main import main
+    main_config_dir = os.path.dirname(main_config)
+    sys.argv = [sys.argv[0]] + sys.argv[3:] + [main_config_dir]
+    main(builtin_parameters)
Index: llvm/utils/lit/tests/Inputs/config-map-discovery/lit.alt.cfg
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/config-map-discovery/lit.alt.cfg
@@ -0,0 +1,9 @@
+import lit.formats
+import lit.util
+config.name = 'config-map'
+config.suffixes = ['.txt']
+config.test_format = lit.formats.ShTest()
+
+import os
+config.test_exec_root = lit.util.norm_path(os.path.dirname(__file__))
+config.test_source_root = os.path.join(config.test_exec_root, "tests")
Index: llvm/utils/lit/tests/Inputs/config-map-discovery/main-config/lit.cfg
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/config-map-discovery/main-config/lit.cfg
@@ -0,0 +1 @@
+print("ERROR: lit.cfg invoked!")
\ No newline at end of file
Index: llvm/utils/lit/tests/discovery.py
===================================================================
--- llvm/utils/lit/tests/discovery.py
+++ llvm/utils/lit/tests/discovery.py
@@ -25,6 +25,26 @@
 # CHECK-BASIC-OUT: top-level-suite :: test-one
 # CHECK-BASIC-OUT: top-level-suite :: test-two
 
+# Check discovery when providing the special builtin 'config_map'
+# RUN: %{python} %{inputs}/config-map-discovery/driver.py \
+# RUN:           %{inputs}/config-map-discovery/main-config/lit.cfg \
+# RUN:           %{inputs}/config-map-discovery/lit.alt.cfg \
+# RUN:           --single-process --debug --show-tests --show-suites > %t.out 2> %t.err
+# RUN: FileCheck --check-prefix=CHECK-CONFIG-MAP-OUT < %t.out %s
+# RUN: FileCheck --check-prefix=CHECK-CONFIG-MAP-ERR < %t.err %s
+
+# CHECK-CONFIG-MAP-OUT: -- Test Suites --
+# CHECK-CONFIG-MAP-OUT:   config-map - 2 tests
+# CHECK-CONFIG-MAP-OUT:     Source Root: {{.*[/\\]config-map-discovery[/\\]tests}}
+# CHECK-CONFIG-MAP-OUT:     Exec Root  : {{.*[/\\]tests[/\\]inputs[/\\]config-map-discovery}}
+# CHECK-CONFIG-MAP-OUT: -- Available Tests --
+# CHECK-CONFIG-MAP-OUT:   config-map :: test1.txt
+# CHECK-CONFIG-MAP-OUT:   config-map :: test2.txt
+
+# CHECK-CONFIG-MAP-ERR: loading suite config '{{.*}}lit.alt.cfg'
+# CHECK-CONFIG-MAP-ERR: loaded config '{{.*}}lit.alt.cfg'
+# CHECK-CONFIG-MAP-ERR: resolved input '{{.*config-map-discovery[/\\]main-config}}' to 'config-map'::()
+
 
 # Check discovery when exact test names are given.
 #