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

Peter Wu via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Mon May 22 02:10:23 PDT 2017

Lekensteyn added inline comments.

Comment at: include/clang/ASTMatchers/Dynamic/VariantValue.h:335
     unsigned Unsigned;
+    double Double;
     bool Boolean;
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).

Comment at: lib/ASTMatchers/Dynamic/Parser.cpp:209
+      double doubleValue = strtod(Result->Text.str().c_str(), &end);
+      if (*end == 0) {
+        Result->Kind = TokenInfo::TK_Literal;
aaron.ballman wrote:
> You're failing to check errno here to ensure the value is actually valid.
will check this later, see also the previous comment


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