[Driver] Execute the frontend when invoked via swift-frontend.

This obviates the need for "-frontend", although we still accept it
for backward compatibility. Switch lit's %target-swift-frontend et al
over to calling swift-frontend.

Author: DougGregor

test/Driver/frontend.swift

@@ -0,0 +1,4 @@
+// RUN: %swiftc_driver %s -### 2>&1 | %FileCheck %s
+
+// CHECK: swift-frontend
+

test/Frontend/crash.swift

@@ -3,7 +3,7 @@
 
 // Check that we see the contents of the input file list in the crash log.
 // CHECK-LABEL: Stack dump
-// CHECK-NEXT: Program arguments: {{.*swift(c?)(\.exe)?}} -frontend
+// CHECK-NEXT: Program arguments: {{.*swift(-frontend)?(c?)(\.exe)?}}
 // CHECK-NEXT: Swift version
 // CHECK-NEXT: Contents of {{.*}}.filelist.txt:
 // CHECK-NEXT: ---

test/lit.cfg

@@ -238,6 +238,7 @@ if 'gmalloc' in lit_config.params:
     config.environment['MALLOC_LOG_FILE'] = '/dev/null'
     config.available_features.add('gmalloc')
 
+config.swift_frontend = inferSwiftBinary('swift-frontend')
 config.swift = inferSwiftBinary('swift')
 config.swiftc = inferSwiftBinary('swiftc')
 config.sil_opt = inferSwiftBinary('sil-opt')
@@ -432,8 +433,8 @@ config.substitutions.append( ('%swift-path', config.swift) )
 # This must come after all substitutions containing "%swift".
 config.substitutions.append(
     ('%swift',
-     "%r -frontend %s -disable-objc-attr-requires-foundation-module %s %s"
-       % (config.swift, mcp_opt, config.swift_test_options, config.swift_frontend_test_options)) )
+     "%r %s -disable-objc-attr-requires-foundation-module %s %s"
+       % (config.swift_frontend, mcp_opt, config.swift_test_options, config.swift_frontend_test_options)) )
 
 config.clang_include_dir = make_path(config.swift, '..', '..', 'include')
 config.substitutions.append( ('%clang-include-dir', config.clang_include_dir) )
@@ -970,12 +971,12 @@ if run_vendor == 'apple':
     if run_os == 'maccatalyst':
         maccatalyst_extra_frameworks = "-F {}/System/iOSSupport/System/Library/Frameworks".format(config.variant_sdk)
     config.target_swift_frontend = (
-        "%s -frontend %s -sdk %r %s %s %s" %
-        (config.swiftc, target_options, config.variant_sdk, maccatalyst_extra_frameworks,
+        "%s %s -sdk %r %s %s %s" %
+        (config.swift_frontend, target_options, config.variant_sdk, maccatalyst_extra_frameworks,
          config.swift_test_options, config.swift_frontend_test_options))
     subst_target_swift_frontend_mock_sdk = (
-        "%s -frontend %s -sdk %r %s %s" %
-        (config.swiftc, target_options_for_mock_sdk, config.variant_sdk,
+        "%s %s -sdk %r %s %s" %
+        (config.swift_frontend, target_options_for_mock_sdk, config.variant_sdk,
          config.swift_test_options, config.swift_frontend_test_options))
     config.target_swift_modulewrap = (
         '%s -modulewrap -target %s' %
@@ -1049,7 +1050,7 @@ elif run_os in ['windows-msvc']:
     config.target_run = ''
 
     config.target_swift_frontend =                                               \
-            ('%r -frontend -target %s %s %s %s %s' % (config.swiftc,             \
+            ('%r -target %s %s %s %s %s' % (config.swift_frontend,             \
                                                       config.variant_triple,     \
                                                       resource_dir_opt, mcp_opt, \
                                                       config.swift_test_options, \
@@ -1174,8 +1175,8 @@ elif (run_os in ['linux-gnu', 'linux-gnueabihf', 'freebsd', 'openbsd', 'windows-
         % (config.target_build_swift))
     config.target_add_rpath = r'-Xlinker -rpath -Xlinker \1'
     config.target_swift_frontend = (
-        '%s -frontend -target %s %s %s %s %s '
-        % (config.swift, config.variant_triple, resource_dir_opt, mcp_opt,
+        '%s -target %s %s %s %s %s '
+        % (config.swift_frontend, config.variant_triple, resource_dir_opt, mcp_opt,
         config.swift_test_options, config.swift_frontend_test_options))
     subst_target_swift_frontend_mock_sdk = config.target_swift_frontend
     subst_target_swift_frontend_mock_sdk_after = ""
@@ -1293,8 +1294,7 @@ elif run_os == 'linux-androideabi' or run_os == 'linux-android':
         '-o', "'\\1'"])
     config.target_add_rpath = r'-Xlinker -rpath -Xlinker \1'
     config.target_swift_frontend = ' '.join([
-        config.swift,
-        '-frontend',
+        config.swift_frontend,
         '-target', config.variant_triple,
         android_include_paths_opt, android_link_paths_opt,
         resource_dir_opt, mcp_opt, config.swift_test_options,
@@ -1370,8 +1370,7 @@ elif run_os == 'wasi':
         % (config.target_build_swift))
     config.target_add_rpath = ''
     config.target_swift_frontend = ' '.join([
-        config.swift,
-        '-frontend',
+        config.swift_frontend,
         '-target', config.variant_triple,
         '-Xcc', '--sysroot=%s' % config.variant_sdk,
         resource_dir_opt, mcp_opt,

tools/driver/driver.cpp

@@ -142,6 +142,14 @@ static int run_driver(StringRef ExecName,
     }
   }
 
+  // Run the integrated Swift frontend when called as "swift-frontend" but
+  // without a leading "-frontend".
+  if (ExecName == "swift-frontend") {
+    return performFrontend(llvm::makeArrayRef(argv.data()+1,
+                                              argv.data()+argv.size()),
+                           argv[0], (void *)(intptr_t)getExecutablePath);
+  }
+
   std::string Path = getExecutablePath(argv[0]);
 
   PrintingDiagnosticConsumer PDC;