[CI] Introduce SPIR-V Backend support in LIT config (#16600)

We introduce here SPIR-V Backend support in LIT config by adding a new
LIT feature 'spirv-backend', and in a way that substitutions in
end-to-end tests are aware about the new LIT feature.

---------

Co-authored-by: aelovikov-intel <andrei.elovikov@intel.com>

Author: VyacheslavLevytskyy

sycl/test-e2e/README.md

@@ -250,6 +250,11 @@ place. No new tests should use these features:
 * **gpu-intel-pvc** - Intel GPU PVC availability;
 * **gpu-intel-pvc-vg** - Intel GPU PVC-VG availability;
 
+### Use the LLVM SPIR-V Backend to generate SPIR-V code
+It's possible to use the LLVM SPIR-V Backend instead of the `llvm-spirv` tool
+to convert LLVM IR to SPIR-V. This feature must be set manually by passing the
+`spirv-backend` parameter to `llvm-lit`.
+
 ### llvm-lit parameters
 
 Following options can be passed to llvm-lit tool through --param option to

sycl/test-e2e/format.py

@@ -183,6 +183,11 @@ def execute(self, test, litConfig):
             )
             sycl_target_opts += hip_arch_opts
             substitutions.append(("%{hip_arch_opts}", hip_arch_opts))
+        if (
+            get_triple("spir64") in triples
+            and "spirv-backend" in test.config.available_features
+        ):
+            sycl_target_opts += " -fsycl-use-spirv-backend-for-spirv-gen"
         substitutions.append(("%{sycl_target_opts}", sycl_target_opts))
 
         substitutions.append(

sycl/test-e2e/lit.cfg.py

@@ -225,6 +225,8 @@ def check_igc_tag_and_add_feature():
 if lit_config.params.get("enable-perf-tests", False):
     config.available_features.add("enable-perf-tests")
 
+if lit_config.params.get("spirv-backend", False):
+    config.available_features.add("spirv-backend")
 
 # Use this to make sure that any dynamic checks below are done in the build
 # directory and not where the sources are located. This is important for the