[lldb] [lit] Add feature flags for native CPU features

[mgorny]

Summary

Add a new lit-cpuid tool that detects CPU features used by some of
the tests, and use it to populate available_features in lit. For now,
this means that the test for MM/XMM register read will be run only
when the host CPU support SSE instruction set. However, this is going
to make it possible to introduce additional tests relying on AVX.

[labath]

I like this approach, but as this is a novel idea, I'd like to get more opinions first. @JDevlieghere, what do you think?

lldb/lit/lit.cfg.py

81

So if the binary is not found for any reason, this will just silently skip the relevant tests, right? Would it make sense to at least print a warning in this case?

[mgorny]

lldb/lit/lit.cfg.py

81

Yes, it will skip them. I don't have an opinion on whether it's something we should warn about; but I can surely add one.

[JDevlieghere]

I really like this too, it's conceptually simple, easy to use and allows us to write more tests in lit. Thanks for doing this Michał.

lldb/lit/lit.cfg.py

81

I agree it would be good to print a warning. We're the ones building the tool so there's really no good reason for it not to be found.

[mgorny]

Added warnings for missing or failed lit-cpuid. Not that there any failure conditions in the program right now ;-).

lldb/CMakeLists.txt

if(TARGET dsymutil)
     list(APPEND LLDB_TEST_DEPS dsymutil)
   endif()
 
   add_custom_target(lldb-test-deps DEPENDS ${LLDB_TEST_DEPS})
 
   add_subdirectory(test)
   add_subdirectory(unittests)
   add_subdirectory(lit)
+  add_subdirectory(utils/lit-cpuid)
   add_subdirectory(utils/lldb-dotest)
 endif()
 
 if (NOT LLDB_DISABLE_PYTHON)
     if(NOT LLDB_BUILD_FRAMEWORK)
       set(use_python_wrapper_from_src_dir -m)
     endif()
     if(LLDB_USE_SYSTEM_SIX)

lldb/lit/CMakeLists.txt

 
 string(REPLACE ${CMAKE_CFG_INTDIR} ${LLVM_BUILD_MODE} LLDB_LIBS_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR})
 string(REPLACE ${CMAKE_CFG_INTDIR} ${LLVM_BUILD_MODE} LLDB_TOOLS_DIR ${LLVM_RUNTIME_OUTPUT_INTDIR})
 string(REPLACE ${CMAKE_CFG_INTDIR} ${LLVM_BUILD_MODE} LLDB_DOTEST_ARGS "${LLDB_DOTEST_ARGS}")
 
 list(APPEND LLDB_TEST_DEPS
   LLDBUnitTests
   dsymutil
+  lit-cpuid
   llc
   lldb
   lldb-test
   llvm-config
   llvm-mc
   llvm-objcopy
   llvm-readobj
   )

lldb/lit/Register/x86-mm-xmm-read.test

 # XFAIL: system-darwin
 # XFAIL: system-windows
-# REQUIRES: native && (target-x86 || target-x86_64)
+# REQUIRES: native && (target-x86 || target-x86_64) && native-cpu-sse
 # RUN: %clangxx %p/Inputs/x86-mm-xmm-read.cpp -o %t
 # RUN: %lldb -b -s %s %t | FileCheck %s
 process launch
 
 register read --all
 # CHECK-DAG: mm0 = 0x0102030405060708
 # CHECK-DAG: mm1 = 0x1112131415161718
 # CHECK-DAG: mm2 = 0x2122232425262728

lldb/lit/lit.cfg.py

 # so doing it once per lit.py invocation is close enough.
 
 for i in ['module-cache-clang', 'module-cache-lldb']:
     cachedir = os.path.join(config.lldb_libs_dir, '..',
                             'lldb-test-build.noindex', i)
     if os.path.isdir(cachedir):
         print("Deleting module cache at %s."%cachedir)
         shutil.rmtree(cachedir)
+
+# If running tests natively, check for CPU features needed for some tests.
+
+if 'native' in config.available_features:
+    cpuid_exe = lit.util.which('lit-cpuid', config.lldb_tools_dir)
+    if cpuid_exe is None:
+        lit_config.warning("lit-cpuid not found, tests requiring CPU extensions will be skipped")
+    else:
+        out, err, exitcode = lit.util.executeCommand([cpuid_exe])
+        if exitcode == 0:
+            for x in out.split():
+                config.available_features.add('native-cpu-%s' % x)
+        else:
+            lit_config.warning("lit-cpuid failed: %s" % err)

lldb/utils/lit-cpuid/CMakeLists.txt

+add_llvm_utility(lit-cpuid
+  lit-cpuid.cpp
+  )
+
+target_link_libraries(lit-cpuid PRIVATE LLVMSupport)

lldb/utils/lit-cpuid/lit-cpuid.cpp

+//===- lit-cpuid.cpp - Get CPU feature flags for lit exported features ----===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// lit-cpuid obtains the feature list for the currently running CPU, and outputs
+// those flags that are interesting for LLDB lit tests.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/StringMap.h"
+#include "llvm/Support/Host.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+int main(int argc, char **argv) {
+#if defined(__i386__) || defined(_M_IX86) || \
+    defined(__x86_64__) || defined(_M_X64)
+  StringMap<bool> features;
+
+  if (!sys::getHostCPUFeatures(features))
+    return 1;
+
+  if (features["sse"])
+    outs() << "sse\n";
+#endif
+
+  return 0;
+}