[all-commits] [llvm/llvm-project] 95114f: [clang][cli] Do not marshall only CC1Option flags ...

[Jan Svoboda via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 95114f21f5bf1704672dadb45ca7c25efca72e03
      https://github.com/llvm/llvm-project/commit/95114f21f5bf1704672dadb45ca7c25efca72e03
  Author: Jan Svoboda <jan_svoboda at apple.com>
  Date:   2020-12-16 (Wed, 16 Dec 2020)

  Changed paths:
    M clang/include/clang/Driver/Options.td
    M clang/lib/Frontend/CompilerInvocation.cpp
    M clang/unittests/Frontend/CompilerInvocationTest.cpp

  Log Message:
  -----------
  [clang][cli] Do not marshall only CC1Option flags in BoolOption

We cannot be sure whether a flag is CC1Option inside the definition of `BoolOption`. Take the example below:

```
let Flags = [CC1Option] in {
  defm xxx : BoolOption<...>;
}
```

where TableGen applies `Flags = [CC1Option]` to the `xxx` and `no_xxx` records **after** they have been is fully declared by `BoolOption`.

For the refactored `-f[no-]debug-pass-manager` flags (see the diff), this means `BoolOption` never adds any marshalling info, as it doesn't see either of the flags as `CC1Option`.

For that reason, we should defensively append the marshalling information to both flags inside `BoolOption`. Now the check for `CC1Option` needs to happen later, in the parsing macro, when all TableGen logic has been resolved.

However, for some flags defined through `BoolOption`, we can run into issues:

```
// Options.td
def fenable_xxx : /* ... */;

// Both flags are CC1Option, the first is implied.
defm xxx : BoolOption<"xxx,
  "Opts.Xxx", DefaultsToFalse,
  ChangedBy<PosFlag, [CC1Option], "", [fenable_xxx]>,
  ResetBy<NegFlag, [CC1Option]>>;
```

When parsing `clang -cc1 -fenable-xxx`:
* we run parsing for `PosFlag`:
  * set `Opts.Xxx` to default `false`,
  * discover `PosFlag` is implied by `-fenable-xxx`: set `Opts.Xxx` to `true`,
  * don't see `-fxxx` on command line: do nothing,
* we run parsing for `NegFlag`:
  * set `Opts.Xxx` to default `false`,
  * discover `NegFlag` cannot be implied: do nothing,
  * don't see `-fno-xxx` on command line: do nothing.

Now we ended up with `Opts.Xxx` set to `false` instead of `true`. For this reason, we need to ensure to append the same `ImpliedByAnyOf` instance to both flags.

This means both parsing runs now behave identically (they set the same default value, run the same "implied by" check, and call `makeBooleanOptionNormalizer` that already has information on both flags, so it returns the same value in both calls).

The solution works well, but what might be confusing is this: you have defined a flag **A** that is not `CC1Option`, but can be implied by another flag **B** that is `CC1Option`:
* if **A** is defined manually, it will never get implied, as the code never runs
```
def no_signed_zeros : Flag<["-"], "fno-signed-zeros">, Group<f_Group>, Flags<[]>,
  MarshallingInfoFlag<"LangOpts->NoSignedZero">, ImpliedByAnyOf<[menable_unsafe_fp_math]>;
```
* if **A** is defined by `BoolOption`, it could get implied, as the code is run by its `CC1Option` counterpart:
```
defm signed_zeros : BoolOption<"signed-zeros",
  "LangOpts->NoSignedZero", DefaultsToFalse,
  ChangedBy<NegFlag, [], "Allow optimizations that ignore the sign of floating point zeros",
            [cl_no_signed_zeros, menable_unsafe_fp_math]>,
  ResetBy<PosFlag, [CC1Option]>, "f">, Group<f_Group>;
```

This is a surprising inconsistency.

One solution might be to somehow propagate the final `Flags` of the implied flag in `ImpliedByAnyOf` and check whether it has `CC1Option` in the parsing macro. However, I think it doesn't make sense to spend time thinking about a corner case that won't come up in real code.

An observation: it is unfortunate that the marshalling information is a part of the flag definition. If we represented it in a separate structure, we could avoid the "double parsing" problem by having a single source of truth. This would require a lot of additional work though.

Note: the original patch missed the `CC1Option` check in the parsing macro, making my reasoning here incomplete. Moreover, it contained a change to denormalization that wasn't necessarily related to these changes, so I've extracted that to a follow-up patch: D93094.

Reviewed By: dexonsmith, Bigcheese

Differential Revision: https://reviews.llvm.org/D93008


  Commit: f2661bed185e14a8f5aa9a54565a8b938a7a10aa
      https://github.com/llvm/llvm-project/commit/f2661bed185e14a8f5aa9a54565a8b938a7a10aa
  Author: Jan Svoboda <jan_svoboda at apple.com>
  Date:   2020-12-16 (Wed, 16 Dec 2020)

  Changed paths:
    M clang/include/clang/Driver/Options.td
    M clang/lib/Frontend/CompilerInvocation.cpp
    M clang/unittests/Frontend/CompilerInvocationTest.cpp
    M llvm/include/llvm/Option/OptParser.td

  Log Message:
  -----------
  [clang][cli] Prevent double denormalization

If both flags created through BoolOption are CC1Option and the keypath has a non-default or non-implied value, the denormalizer gets called twice. If the denormalizer has the ability to generate both flags, we can end up generating the same flag twice.

Reviewed By: dexonsmith, Bigcheese

Differential Revision: https://reviews.llvm.org/D93094


Compare: https://github.com/llvm/llvm-project/compare/b2851aea80e5...f2661bed185e