[cfe-commits] [Review] rollingout ASTContext::getTypeSizeInBytes()

John McCall rjmccall at apple.com
Wed Nov 25 13:08:57 PST 2009

Ken Dyck wrote:
> On Tuesday, November 24, 2009 5:13 PM, John McCall wrote:
>> Ted Kremenek wrote:
>>> I agree with John.  If we're rolling out a new API why not 
>> introduce 
>>> now a new type that adds the "dimensionality" of the value?  (bytes 
>>> versus bits)
>>> John: Is that what you meant?
>> Yeah.  I am fairly skeptical of this feature surviving 
>> correctly otherwise.
> Okay. I'll take a stab at implementing this. 
> As I understand it, these are the changes that need to happen:
> 1. Remove the recently added ASTContext::getByteSize() and
> ASTContext::getTypeSizeInBytes().
> 2. Add a new class (named TypeSize, say) that has two methods: inBits()
> and inBytes().
> 3. Change the return type of ASTContext::getTypeSize() from uint64_t to
> TypeSize.
> 4. Update all calls to getTypeSize() to explicity choose the bit or byte
> size.
> Is this what you had in mind?

That would actually be quite expensive, since every instance would need 
to somehow know how many bits were in a byte.

I was thinking more along the lines of a type that represented a 
size/offset in bytes;  call it bytes_t for the sake of argument.  
Anything that returned or required a size in bytes would take one of 
these instead of a raw uint64_t.  It would basically wrap a uint64_t, 
but wouldn't allow implicit conversion to or from any integer type, and 
it would have overloaded operators to do most of the common operations 
on the type, e.g.
  bytes_t operator+(bytes_t, bytes_t);
  bytes_t operator*(bytes_t, uint64_t);
The idea being to make it more difficult to accidentally encode 
byte-size assumptions, as well as to make code more implicitly 

In theory we might also want a bits_t, but that's more awkward without 
support from LLVM.

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