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95114f21f5
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