add a Swift pass which can run unit tests.

The `run-unit-tests` is a "pseudo" pass which is invoked from sil-opt and runs all the unit tests, implemented in Swift.
This is done from the `swift-unit-tests.sil` lit test.

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/CMakeLists.txt

@@ -11,4 +11,5 @@ swift_compiler_sources(Optimizer
   SILPrinter.swift
   MergeCondFails.swift
   ReleaseDevirtualizer.swift
+  RunUnitTests.swift
 )

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/RunUnitTests.swift

@@ -0,0 +1,21 @@
+//===--- UnitTests.swift - A pseudo pass for running the unit tests -------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SIL
+
+/// This pass should only be used by sil-opt to run all the unit tests.
+///
+let runUnitTests = FunctionPass(name: "run-unit-tests", {
+  (function: Function, context: PassContext) in
+
+  print("--- Run unit tests ---")
+})

SwiftCompilerSources/Sources/Optimizer/PassManager/PassRegistration.swift

@@ -51,5 +51,6 @@ private func registerSwiftPasses() {
   registerPass(simplifyStrongRetainPass, { simplifyStrongRetainPass.run($0) })
   registerPass(simplifyStrongReleasePass, { simplifyStrongReleasePass.run($0) })
   registerPass(assumeSingleThreadedPass, { assumeSingleThreadedPass.run($0) })
+  registerPass(runUnitTests, { runUnitTests.run($0) })
   registerPass(releaseDevirtualizerPass, { releaseDevirtualizerPass.run($0) })
 }

include/swift/SILOptimizer/PassManager/Passes.def

@@ -368,6 +368,8 @@ PASS(SILDebugInfoGenerator, "sil-debuginfo-gen",
      "Generate Debug Information with Source Locations into Textual SIL")
 PASS(EarlySROA, "early-sroa",
      "Scalar Replacement of Aggregate Stack Objects on high-level SIL")
+SWIFT_FUNCTION_PASS(RunUnitTests, "run-unit-tests",
+     "Runs the compiler internal unit tests")
 SWIFT_FUNCTION_PASS(SILPrinter, "sil-printer",
      "Test pass which prints the SIL of a function")
 PASS(SROA, "sroa",

test/SILOptimizer/swift-unit-tests.sil

@@ -0,0 +1,11 @@
+// RUN: %target-sil-opt %s -run-unit-tests -o /dev/null
+
+// REQUIRES: swift_in_compiler
+
+// The RunUnitTests is a function pass. Therefore we need one function is this file to trigger the pass run.
+sil @trigger_test_run : $@convention(thin) () -> () {
+bb0:
+  %r = tuple()
+  return %r : $()
+}
+