Merge pull request #18318 from eeckstein/add-bm-option

IRGen, benchmarks: add an option -align-module-to-page-size for benchmarking

Author: eeckstein

benchmark/CMakeLists.txt

@@ -272,6 +272,7 @@ message("--   SWIFT_LIBRARY_PATH = ${SWIFT_LIBRARY_PATH}")
 message("--   CLANG_EXEC = ${CLANG_EXEC}")
 message("--   SWIFT_OPTIMIZATION_LEVELS = ${SWIFT_OPTIMIZATION_LEVELS}")
 message("--   ONLY_PLATFORMS = ${ONLY_PLATFORMS}")
+message("--   PAGE_ALIGNMENT_OPTION = ${PAGE_ALIGNMENT_OPTION}")
 
 message("--   found platforms: ${platforms}")
 message("--   found sdks:")

benchmark/cmake/modules/AddSwiftBenchmarkSuite.cmake

@@ -40,6 +40,19 @@ macro(configure_build)
     message(FATAL_ERROR "Unsupported platform?!")
   endif()
 
+  set(PAGE_ALIGNMENT_OPTION "-Xllvm" "-align-module-to-page-size")
+  execute_process(
+      COMMAND "touch" "empty.swift"
+      RESULT_VARIABLE result
+      ERROR_QUIET OUTPUT_STRIP_TRAILING_WHITESPACE)
+  execute_process(
+      COMMAND "${SWIFT_EXEC}" ${PAGE_ALIGNMENT_OPTION} "empty.swift"
+      RESULT_VARIABLE result
+      ERROR_QUIET OUTPUT_STRIP_TRAILING_WHITESPACE)
+  if(NOT "${result}" MATCHES "0")
+    set(PAGE_ALIGNMENT_OPTION "")
+  endif()
+
   # We always infer the SWIFT_LIBRARY_PATH from SWIFT_EXEC unless
   # SWIFT_LIBRARY_PATH is specified explicitly.
   if(NOT SWIFT_LIBRARY_PATH)
@@ -293,7 +306,7 @@ function (swift_benchmark_compile_archopts)
   set(common_options
       "-c"
       "-target" "${target}"
-      "-${BENCH_COMPILE_ARCHOPTS_OPT}")
+      "-${BENCH_COMPILE_ARCHOPTS_OPT}" ${PAGE_ALIGNMENT_OPTION})
 
   if (is_darwin)
     list(APPEND common_options

lib/IRGen/IRGen.cpp

@@ -74,6 +74,10 @@
 
 #include <thread>
 
+#if HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
 using namespace swift;
 using namespace irgen;
 using namespace llvm;
@@ -82,6 +86,14 @@ static cl::opt<bool> DisableObjCARCContract(
     "disable-objc-arc-contract", cl::Hidden,
     cl::desc("Disable running objc arc contract for testing purposes"));
 
+// This option is for performance benchmarking: to ensure a consistent
+// performance data, modules are aligned to the page size.
+// Warning: this blows up the text segment size. So use this option only for
+// performance benchmarking.
+static cl::opt<bool> AlignModuleToPageSize(
+    "align-module-to-page-size", cl::Hidden,
+    cl::desc("Align the text section of all LLVM modules to the page size"));
+
 namespace {
 // We need this to access IRGenOptions from extension functions
 class PassManagerBuilderWrapper : public PassManagerBuilder {
@@ -274,6 +286,23 @@ void swift::performLLVMOptimizations(IRGenOptions &Opts, llvm::Module *Module,
 
   // Do it.
   ModulePasses.run(*Module);
+
+  if (AlignModuleToPageSize) {
+    // For performance benchmarking: Align the module to the page size by
+    // aligning the first function of the module.
+    unsigned pageSize =
+#if HAVE_UNISTD_H
+      sysconf(_SC_PAGESIZE));
+#else
+      4096; // Use a default value
+#endif
+    for (auto I = Module->begin(), E = Module->end(); I != E; ++I) {
+      if (!I->isDeclaration()) {
+        I->setAlignment(pageSize);
+        break;
+      }
+    }
+  }
 }
 
 namespace {