[PATCH] D119601: [analyzer] Refactor makeNull to makeNullWithWidth (NFC)

[Vince Bridgers via Phabricator via cfe-commits]

vabridgers added inline comments.


================
Comment at: clang/include/clang/StaticAnalyzer/Core/PathSensitive/SValBuilder.h:378
+    type = type->isReferenceType()
+               ? Context.getPointerType(type->getPointeeType())
+               : type;
----------------
NoQ wrote:
> vabridgers wrote:
> > NoQ wrote:
> > > How do you discover the pointer width by looking only at the pointee type? Are objects of specific type always restricted to a specific address space? I.e., does every `int *` have the same width everywhere in the program? If not, how is this code supposed to work?
> > The case this code addresses is represented in the test case clang/test/Analysis/cast-value-notes.cpp, this function ...
> > 
> > ```
> >  24 void evalReferences(const Shape &S) {
> >  25   const auto &C = dyn_cast<Circle>(S);
> >  26   // expected-note at -1 {{Assuming 'S' is not a 'Circle'}}
> >  27   // expected-note at -2 {{Dereference of null pointer}}
> >  28   // expected-warning at -3 {{Dereference of null pointer}}
> >  29 }
> > 
> > ```
> > The crash occurs from line 25 above. 
> > 
> > Debug printing what I see at this point in the code for this case ...
> > 
> > ```
> > QualType type : LValueReferenceType 0xffea820 'const class clang::Circle &'
> > `-QualType 0xffea7c1 'const class clang::Circle' const
> >   `-SubstTemplateTypeParmType 0xffea7c0 'class clang::Circle' sugar
> >     |-TemplateTypeParmType 0xffe4f90 'X' dependent depth 0 index 0
> >     | `-TemplateTypeParm 0xffe4f40 'X'
> >     `-RecordType 0xffea090 'class clang::Circle'
> >       `-CXXRecord 0xffea000 'Circle'
> > 
> > Context.getPointerType(type) : PointerType 0x10006ab0 'const class clang::Circle &*'
> > `-LValueReferenceType 0xffea820 'const class clang::Circle &'
> >   `-QualType 0xffea7c1 'const class clang::Circle' const
> >     `-SubstTemplateTypeParmType 0xffea7c0 'class clang::Circle' sugar
> >       |-TemplateTypeParmType 0xffe4f90 'X' dependent depth 0 index 0
> >       | `-TemplateTypeParm 0xffe4f40 'X'
> >       `-RecordType 0xffea090 'class clang::Circle'
> >         `-CXXRecord 0xffea000 'Circle'
> > 
> > Context.getPointerType(type->getPointeeType()) : PointerType 0x10006ae0 'const class clang::Circle *'
> > `-QualType 0xffea7c1 'const class clang::Circle' const
> >   `-SubstTemplateTypeParmType 0xffea7c0 'class clang::Circle' sugar
> >     |-TemplateTypeParmType 0xffe4f90 'X' dependent depth 0 index 0
> >     | `-TemplateTypeParm 0xffe4f40 'X'
> >     `-RecordType 0xffea090 'class clang::Circle'
> >       `-CXXRecord 0xffea000 'Circle'
> > 
> > ```
> > The LValueReferenceType causes a crash if I do not get a pointer type, looks like ... 
> > 
> > ```
> > clang:  <root>/clang/include/clang/StaticAnalyzer/Core/PathSensitive/BasicValueFactory.h:219: const llvm::APSInt& clang::ento::BasicValueFactory::getZeroWithTypeSize(clang::QualType): Assertion `T->isScalarType()' failed.
> > 
> > ```
> > I'm assuming the pointer type retains the address space attribute of the LValueReferenceType. 
> > 
> > Context.getPointerType(type->getPointeeType()) produces a QualType :  PointerType 'const class clang::Circle *' from an original QualType : LValueReferenceType 'const class clang::Circle &'
> > 
> > Is this not what's wanted - a pointer type instead of a reference, with the same address space qualifiers, or am I missing something in the query? 
> > 
> > Thanks
> Do I understand correctly that `__attribute__((address_space))` is a type attribute that gets applied to values rather than to pointers, so `__attribute__((address_space(3))) int *x` defines `x` as "pointer to (int that lives in address_space(3))", so when you unwrap the pointer type you get an "int that lives in address_space(3)"?
> 
> Can you share some dumps to demonstrate that the attribute is correctly preserved by this procedure? Damn, a test case could be great if we could have them.
I'll see what can be done about a test case, and provide the dumps for evaluation. Best


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D119601/new/

https://reviews.llvm.org/D119601