0x8000-0000 added inline comments.
================
Comment at: clang-tidy/readability/MagicNumbersCheck.cpp:76-86
+ IgnoredFloatingPointValues.reserve(IgnoredFloatingPointValuesInput.size());
+ IgnoredDoublePointValues.reserve(IgnoredFloatingPointValuesInput.size());
+ for (const auto &InputValue : IgnoredFloatingPointValuesInput) {
+ llvm::APFloat FloatValue(llvm::APFloat::IEEEsingle());
+ FloatValue.convertFromString(InputValue, DefaultRoundingMode);
+ IgnoredFloatingPointValues.push_back(FloatValue.convertToFloat());
+
----------------
0x8000-0000 wrote:
> 0x8000-0000 wrote:
> > aaron.ballman wrote:
> > > aaron.ballman wrote:
> > > > 0x8000-0000 wrote:
> > > > > 0x8000-0000 wrote:
> > > > > > 0x8000-0000 wrote:
> > > > > > > 0x8000-0000 wrote:
> > > > > > > > 0x8000-0000 wrote:
> > > > > > > > > aaron.ballman wrote:
> > > > > > > > > > 0x8000-0000 wrote:
> > > > > > > > > > > aaron.ballman wrote:
> > > > > > > > > > > > 0x8000-0000 wrote:
> > > > > > > > > > > > > aaron.ballman wrote:
> > > > > > > > > > > > > > This is where I would construct an `APFloat` object
> > > > > > > > > > > > > > from the string given. As for the semantics to be
> > > > > > > > > > > > > > used, I would recommend getting it from
> > > > > > > > > > > > > > `TargetInfo::getDoubleFormat()` on the belief that
> > > > > > > > > > > > > > we aren't going to care about precision (explained
> > > > > > > > > > > > > > in the documentation).
> > > > > > > > > > > > > Here is the problem I tried to explain last night but
> > > > > > > > > > > > > perhaps I wasn't clear enough.
> > > > > > > > > > > > >
> > > > > > > > > > > > > When we parse the input list from strings, we have to
> > > > > > > > > > > > > commit to one floating point value "semantic" - in
> > > > > > > > > > > > > our case single or double precision.
> > > > > > > > > > > > >
> > > > > > > > > > > > > When we encounter the value in the source code and it
> > > > > > > > > > > > > is captured by a matcher, it comes as either one of
> > > > > > > > > > > > > those values.
> > > > > > > > > > > > >
> > > > > > > > > > > > > Floats with different semantics can't be directly
> > > > > > > > > > > > > compared - so we have to maintain two distinct arrays.
> > > > > > > > > > > > >
> > > > > > > > > > > > > If we do that, rather than store APFloats and
> > > > > > > > > > > > > sort/compare them with awkward lambdas, we might as
> > > > > > > > > > > > > well just use the native float/double and be done
> > > > > > > > > > > > > with it more cleanly.
> > > > > > > > > > > > >When we encounter the value in the source code and it
> > > > > > > > > > > > >is captured by a matcher, it comes as either one of
> > > > > > > > > > > > >those values.
> > > > > > > > > > > >
> > > > > > > > > > > > It may also come in as long double or __float128, for
> > > > > > > > > > > > instance, because there are type suffixes for that.
> > > > > > > > > > > >
> > > > > > > > > > > > > Floats with different semantics can't be directly
> > > > > > > > > > > > > compared - so we have to maintain two distinct arrays.
> > > > > > > > > > > >
> > > > > > > > > > > > Yes, floats with different semantics cannot be directly
> > > > > > > > > > > > compared. That's why I said below that we should coerce
> > > > > > > > > > > > the literal values.
> > > > > > > > > > > >
> > > > > > > > > > > > > If we do that, rather than store APFloats and
> > > > > > > > > > > > > sort/compare them with awkward lambdas, we might as
> > > > > > > > > > > > > well just use the native float/double and be done
> > > > > > > > > > > > > with it more cleanly.
> > > > > > > > > > > >
> > > > > > > > > > > > There are too many different floating-point semantics
> > > > > > > > > > > > for this to be viable, hence why coercion is a
> > > > > > > > > > > > reasonable behavior.
> > > > > > > > > > > Let me see if I understood it - your proposal is: store
> > > > > > > > > > > only doubles, and when a floating-point literal is
> > > > > > > > > > > encountered in code, do not use the FloatingLiteral
> > > > > > > > > > > instance, but parse it again into a double and compare
> > > > > > > > > > > exactly. If the comparison matches - ignore it.
> > > > > > > > > > >
> > > > > > > > > > > In that case what is the value of storing APFloats with
> > > > > > > > > > > double semantics in the IgnoredValues array, instead of
> > > > > > > > > > > doubles?
> > > > > > > > > > > Let me see if I understood it - your proposal is: store
> > > > > > > > > > > only doubles, and when a floating-point literal is
> > > > > > > > > > > encountered in code, do not use the FloatingLiteral
> > > > > > > > > > > instance, but parse it again into a double and compare
> > > > > > > > > > > exactly. If the comparison matches - ignore it.
> > > > > > > > > >
> > > > > > > > > > My proposal is to use `APFloat` as the storage and
> > > > > > > > > > comparison medium. Read in strings from the configuration
> > > > > > > > > > and convert them to an `APFloat` that has double semantics.
> > > > > > > > > > Read in literals and call `FloatLiteral::getValue()` to get
> > > > > > > > > > the `APFloat` from it, convert it to one that has double
> > > > > > > > > > semantics as needed, then perform the comparison between
> > > > > > > > > > those two `APFloat` objects.
> > > > > > > > > >
> > > > > > > > > > > In that case what is the value of storing APFloats with
> > > > > > > > > > > double semantics in the IgnoredValues array, instead of
> > > > > > > > > > > doubles?
> > > > > > > > > >
> > > > > > > > > > Mostly that it allows us to modify or extend the check for
> > > > > > > > > > more complicated semantics in the future. Also, it's good
> > > > > > > > > > practice to use something with consistent semantic behavior
> > > > > > > > > > across hosts and targets (comparisons between numbers that
> > > > > > > > > > cannot be precisely represented will at least be
> > > > > > > > > > consistently compared across hosts when compiling for the
> > > > > > > > > > same target).
> > > > > > > > > >
> > > > > > > > > ok - coming right up!
> > > > > > > > > My proposal is to use APFloat as the storage and comparison
> > > > > > > > > medium. Read in strings from the configuration and convert
> > > > > > > > > them to an APFloat that has double semantics.
> > > > > > > >
> > > > > > > > This is easy.
> > > > > > > >
> > > > > > > > > Read in literals and call FloatLiteral::getValue() to get the
> > > > > > > > > APFloat from it,
> > > > > > > >
> > > > > > > > this is easy as well,
> > > > > > > >
> > > > > > > > > convert it to one that has double semantics as needed, then
> > > > > > > > > perform the comparison between those two APFloat objects.
> > > > > > > >
> > > > > > > > The conversion methods in `APFloat` only produce
> > > > > > > > plain-old-data-types:
> > > > > > > > ```
> > > > > > > > double convertToDouble() const;
> > > > > > > >
> > > > > > > >
> > > > > > > > float convertToFloat() const;
> > > > > > > > ```
> > > > > > > >
> > > > > > > > There is no
> > > > > > > > ```
> > > > > > > > APFloat convertToOtherSemantics(const fltSemantics &) const;
> > > > > > > > ```
> > > > > > > > method.
> > > > > > > >
> > > > > > > > What I can do is
> > > > > > > > 1. convert the APFloat to float or double, depending on what
> > > > > > > > the semantics is; cast to double then load into an APFloat with
> > > > > > > > double semantics and then search into the set
> > > > > > > > 2. parse the textual representation of the FloatingLiteral
> > > > > > > > directly into an APFloat with double semantics.
> > > > > > > `TargetInfo::getDoubleFormat()` is not accessible directly from
> > > > > > > `ClangTidyContext` or from `MatchFinder`
> > > > > > 2. doesn't quite work; `APFloat.convertFromString` chokes on
> > > > > > `3.14f` ;(
> > > > > Option 1 doesn't work, either:
> > > > > ```
> > > > > llvm::APFloat DoubleFloatValue(llvm::APFloat::IEEEdouble());
> > > > >
> > > > >
> > > > > if (&FloatValue.getSemantics() == &llvm::APFloat::IEEEdouble())
> > > > >
> > > > >
> > > > > DoubleFloatValue = FloatValue;
> > > > >
> > > > >
> > > > > else if (&FloatValue.getSemantics() ==
> > > > > &llvm::APFloat::IEEEsingle()) {
> > > > >
> > > > >
> > > > > const float Value = FloatValue.convertToFloat();
> > > > >
> > > > >
> > > > > DoubleFloatValue = llvm::APFloat(static_cast<double>(Value));
> > > > >
> > > > >
> > > > > }
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > return std::binary_search(IgnoredFloatingPointValues.begin(),
> > > > >
> > > > >
> > > > > IgnoredFloatingPointValues.end(),
> > > > >
> > > > >
> > > > > DoubleFloatValue, compareAPFloats);
> > > > > ```
> > > > > has problems with floating point values that are not integers.
> > > > >
> > > > > Unless somebody knows how to convert APFloats with any semantics into
> > > > > APFloats with double semantics, I'm stuck ;(
> > > > > There is no
> > > > > `APFloat convertToOtherSemantics(const fltSemantics &) const;`
> > > > > method.
> > > > ```
> > > > opStatus convert(const fltSemantics &ToSemantics, roundingMode RM,
> > > > bool *losesInfo);
> > > > ```
> > > > This function does exactly that?
> > > > `TargetInfo::getDoubleFormat()` is not accessible directly from
> > > > `ClangTidyContext` or from `MatchFinder`
> > >
> > > `MatchFinder` has an `ASTContext` object on which you can call
> > > `ASTContext::getTargetInfo()`, I believe.
> > Yes, it does! Thank you!
> Looking at the code, it declares a structure for MatchResult which indeed
> contains an ASTContext. But MatchFinder does not hold a reference to it, it
> is passed into it from a MatchVisitor.
>
> What we would need is to parse the configuration before we start matching
> (either in the constructor or in `::registerMatchers` - and there is no
> visitor available then.
So functionally it works, but it suffers from the same problem as doing the
conversion by hand using the
```static_cast<double>(FloatValue.convertToFloat())```; the resulting value for
3.14f does not match the existing value for 3.14 present in the
IgnoredFloatingPointValues array.
Repository:
rCTE Clang Tools Extra
https://reviews.llvm.org/D49114
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