[llvm-dev] LLVM type.h question

[Chris Lattner via llvm-dev]

Right - this is intended to catch a problem where someone tries to store a value in SubclassData that is too large to fit in the bitfield.

-Chris

> On May 3, 2020, at 4:45 PM, Craig Topper via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Isn't the SubclassData member a 24 bit bitfield? I think the truncation would happen on the assignment to it.
> 
> ~Craig
> 
> 
> On Sun, May 3, 2020 at 4:06 PM James Courtier-Dutton via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> Hi,
> 
> I see this in the Type class:
> 
> unsigned getSubclassData() const { return SubclassData; }
> 
> void setSubclassData(unsigned val) {
>   SubclassData = val;
>   // Ensure we don't have any accidental truncation.
>   assert(getSubclassData() == val && "Subclass data too large for field");
> }
> 
> How will the assert ever get triggered?
> The type is "unsigned" so how can getSubclassData() ever not equal val ?
> Where does the truncation take place?
> 
> Kind Regards
> 
> James
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