[PATCH] D33135: [ASTMatchers] Add support for floatLiterals

[Peter Wu via Phabricator via cfe-commits]

Lekensteyn added a comment.

Rebased patches on latest clang master (trunk), there were no changes in ASTMatchers.
boolean literal patch was unchanged, this floating literal patch was updated to address comments.



================
Comment at: include/clang/ASTMatchers/Dynamic/VariantValue.h:335
     unsigned Unsigned;
+    double Double;
     bool Boolean;
----------------
aaron.ballman wrote:
> 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.
I think I'll keep it like this for now and defer eventual conversion to APValue for a future patch that also makes uint64_t possible. Is that OK?


https://reviews.llvm.org/D33135