aaron.ballman added inline comments.
================
Comment at: include/clang/ASTMatchers/Dynamic/VariantValue.h:335
unsigned Unsigned;
+ double Double;
bool Boolean;
----------------
Lekensteyn wrote:
> aaron.ballman wrote:
> > Lekensteyn wrote:
> > > aaron.ballman wrote:
> > > > This may or may not be a good idea, but do we want to put the values
> > > > into an APFloat rather than a double? My concern with double is that
> > > > (0) it may be subtly different if the user wants a 16- or 32-bit float
> > > > explicitly, (1) it won't be able to represent long double values, or
> > > > quad double.
> > > >
> > > > I'm thinking this value could be passed directly from the C++ API as an
> > > > APFloat, float, or double, or provided using a StringRef for the
> > > > dynamic API.
> > > (32-bit) double values are a superset of (16-bit) float values, that
> > > should be OK.
> > > Long doubles are possible in the AST (e.g. for `0.1L`), but neither C11
> > > nor C++14 seem to define a quad double literal type (so that should be of
> > > a lesser concern).
> > >
> > > Reasons why I chose for double instead of APFloat:
> > > - `strtod` is readily available and does not abort the program. By
> > > contrast, `APFloat(StringRef)` trips on assertions if the input is
> > > invalid.
> > > - I was not sure if the APFloat class can be used in an union.
> > The downside to using `strtod()` is that invalid input is silently
> > accepted. However, assertions on invalid input is certainly not good
> > either. It might be worth modifying `APFloat::convertFromString()` to
> > accept invalid input and return an error.
> >
> > I think instead of an `APFloat`, maybe using an `APValue` for both the
> > `Unsigned` and `Double` fields might work. At the very least, it should
> > give you implementation ideas.
> >
> > There is a quad double literal suffix: `q`. It's only supported on some
> > architectures, however. There are also imaginary numbers (`i`) and half
> > (`h`).
> The strtod conversion was based on parseDouble in
> lib/Support/CommandLine.cpp, so any conversion issues also exist there.
>
> Same question, can APFloat/APValue be used in a union?
>
> float (or quad-double suffixes) are explicitly not supported now in this
> matcher, maybe they can be added later but for now I decided to keep the
> grammar simple (that is, do not express double/float data types via the
> literal).
> The strtod conversion was based on parseDouble in
> lib/Support/CommandLine.cpp, so any conversion issues also exist there.
Good to know.
> Same question, can APFloat/APValue be used in a union?
I believe so, but I've not tried it myself. Also, as I mentioned, `APValue`
demonstrates another implementation strategy in case you cannot use a union
directly.
> float (or quad-double suffixes) are explicitly not supported now in this
> matcher, maybe they can be added later but for now I decided to keep the
> grammar simple (that is, do not express double/float data types via the
> literal).
That's reasonable for an initial implementation.
https://reviews.llvm.org/D33135
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