[SYCL][E2E] Use configure_lit_site_cfg in in-tree builds

This provides the added benefit that it will automatically map the
config paths from the build directories to the corresponding source
ones in `llvm-lit`. With this, one should be able to run lit tests
directly from source paths.

In standalone builds, we don't have access to LLVM's wider
configuration, so the old configuration must remain.

Note also that this changes the configured cfg file's name from
`lit.site.cfg` to `lit.site.cfg.py`, but this aligns us with the
predominant style across the llvm project.

Author: frasercrmck

sycl/test-e2e/CMakeLists.txt

@@ -33,8 +33,17 @@ set(SYCL_E2E_TESTS_LIT_FLAGS "-sv" CACHE STRING "Flags used when running lit")
 
 find_package(Python3 REQUIRED COMPONENTS Interpreter)
 
-configure_file("${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.py.in"
-               "${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg")
+if(SYCL_TEST_E2E_STANDALONE)
+  configure_file("${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.py.in"
+                 "${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg.py")
+else()
+  configure_lit_site_cfg(
+    ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.py.in
+    ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg.py
+    MAIN_CONFIG
+    ${CMAKE_CURRENT_SOURCE_DIR}/lit.cfg.py
+    )
+endif() # Standalone.
 
 if(NOT SYCL_TEST_E2E_STANDALONE)
   list(APPEND SYCL_E2E_TEST_DEPS

sycl/test-e2e/README.md

@@ -56,8 +56,8 @@ cmake -G Ninja ...
 ninja check-sycl-e2e
 ```
 
-In addition to this standalone configuration one can enable `check-sycl-e2e`
-target for the sycl-toolchain workspace/build by specifying
+In addition to this, in an in-tree configuration one can enable
+`check-sycl-e2e` target for the sycl-toolchain workspace/build by specifying
 `SYCL_TEST_E2E_TARGETS` as part of its cmake configuration. For example, like
 this:
 
@@ -67,6 +67,19 @@ CC=<> CXX=<> python llvm/buildbot/configure.py -o build ... \
   --cmake-opt=-DSYCL_E2E_TESTS_LIT_FLAGS="--param;dump_ir=True"``
 ```
 
+In an in-tree build, individual tests or groups of tests can be conveniently
+run directly from their source paths, using the configured `llvm-lit` script:
+
+```
+# Implicitly uses cmake parameters SYCL_BE and SYCL_TARGET_DEVICES, detailed
+# below
+build/bin/llvm-lit -sv sycl/test-e2e/Basic/aspects.cpp
+
+# Explicitly sets SYCL backend and target device(s), overriding SYCL_BE and
+# SYCL_TARGET_DEVICES
+build/bin/llvm-lit -sv --param sycl_be=level_zero --param target_devices=cpu,gpu sycl/test-e2e/Basic/aspects.cpp
+```
+
 # Cmake parameters
 
 These parameters can be used to configure tests: