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());
+
----------------
aaron.ballman wrote:
> 0x8000-0000 wrote:
> > 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.
> Hmm, that's certainly annoying.
>
> @alexfh -- I think we should have access to the ASTContext object from within
> the ClangTidyContext passed in when registering the checks. We already have
> `ClangTidyContext::setASTContext()` that gets called before `createChecks()`
> in `ClangTidyASTConsumerFactory::CreateASTConsumer()`; can you think of a
> reason we should not persist that value in the `ClangTidyContext`? If there
> is a good reason to not persist it, perhaps it would be a reasonable argument
> to be passed to each check's constructor (by threading it through
> `createChecks()`?
```
bool MagicNumbersCheck::isIgnoredValue(const FloatingLiteral *Literal) const {
llvm::APFloat FloatValue = Literal->getValue();
if (FloatValue.isZero())
return true;
else {
bool LosesInfo = true;
const llvm::APFloat::opStatus ConvertStatus = FloatValue.convert(
llvm::APFloat::IEEEdouble(), DefaultRoundingMode, &LosesInfo);
if ((ConvertStatus == llvm::APFloat::opOK) ||
(ConvertStatus == llvm::APFloat::opInexact))
return std::binary_search(IgnoredFloatingPointValues.begin(),
IgnoredFloatingPointValues.end(), FloatValue,
compareAPFloats);
else
return false;
}
}
```
"3.14f" FloatValue converts cleanly... to something that is not present in the
IgnoredFloatingPointValues set.
Repository:
rCTE Clang Tools Extra
https://reviews.llvm.org/D49114
_______________________________________________
cfe-commits mailing list
[email protected]
http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
