[clang][cli] Don't always emit -f[no-]legacy-pass-manager

[jansvoboda11]

Summary

We don't need to always generate -f[no-]experimental-new-pass-manager.

This patch does not change the behavior of any other command line flag. (For example -triple is still being always generated.)

[dexonsmith]

This seems fine to me, I agree this option doesn't need to be present all the time. Thanks for clarifying that -triple is still there.

@Bigcheese, WDYT?

[Bigcheese]

LGTM. I don't see any reason to always emit this option.

[jansvoboda11]

Rebase

[jansvoboda11]

Extract default value

[jansvoboda11]

Rebase

[dexonsmith]

LGTM too.

clang/unittests/Frontend/CompilerInvocationTest.cpp

 //===- unittests/Frontend/CompilerInvocationTest.cpp - CI tests //---------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
TEST_F(CommandLineTest, BoolOptionDefaultArbitraryTwoFlagsPresentNeg) {
   const char *Args[] = {"-fno-experimental-new-pass-manager"};
 
   CompilerInvocation::CreateFromArgs(Invocation, Args, *Diags);
   ASSERT_FALSE(Diags->hasErrorOccurred());
   ASSERT_FALSE(Invocation.getCodeGenOpts().ExperimentalNewPassManager);
 
   Invocation.generateCC1CommandLine(GeneratedArgs, *this);
   ASSERT_THAT(GeneratedArgs,
-              Contains(StrEq("-fno-experimental-new-pass-manager")));
+              Not(Contains(StrEq("-fno-experimental-new-pass-manager"))));
   ASSERT_THAT(GeneratedArgs,
               Not(Contains(StrEq("-fexperimental-new-pass-manager"))));
 }
 
 TEST_F(CommandLineTest, CanGenerateCC1CommandLineFlag) {
   const char *Args[] = {"-fmodules-strict-context-hash"};
 
   CompilerInvocation::CreateFromArgs(Invocation, Args, *Diags);

llvm/include/llvm/Option/OptParser.td

class MarshallingInfoBitfieldFlag<code keypath, code value>
   : MarshallingInfoFlag<keypath, "0u"> {
   code Normalizer = "makeFlagToValueNormalizer("#value#")";
   code ValueMerger = "mergeMaskValue";
   code ValueExtractor = "(extractMaskValue<unsigned, decltype("#value#"), "#value#">)";
 }
 
 class MarshallingInfoBooleanFlag<code keypath, code defaultvalue, code neg_name, string neg_spelling>
   : MarshallingInfoFlag<keypath, defaultvalue> {
-  bit ShouldAlwaysEmit = 1;
   code Normalizer = "makeBooleanFlagNormalizer(OPT_"#neg_name#")";
   code Denormalizer = "makeBooleanFlagDenormalizer(\""#neg_spelling#"\")";
 }
 
 // Mixins for additional marshalling attributes.
 
 class IsNegative {
   code Normalizer = "normalizeSimpleNegativeFlag";