[llvm-dev] Semantics of LLVM IR intermediate variables

[Mehdi AMINI via llvm-dev]

On Fri, Oct 25, 2019 at 12:57 AM Jason Thomas via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
> Hi all,
>
> This question may sound stupid, but every time I look at the IR, I take
> some time to convince myself the following:
>
> The following C source code:
>
> 1 int x ;
> 2 int * p ;
> 3 p = & x ;
>
> when compiled to LLVM IR using clang generates the following instructions:
>
> 1 % x = alloca i32 , align 4
> 2 % p = alloca i32 * , align 8
> 3 store i32 * %x , i32 ** %p , align 8
>
> All the local variables in the C source code, i.e. 'x' and 'p' are
> pointers now, in fact they are pointers with one level deeper nesting
> level. What I mean is, 'x' is an 'int' in the C source, but '%x' is 'i32*'.
> 'p' is 'int*' in the C source, but '%p' is 'i32**'. Doesn't it make the IR
> naming convention a misnoer compared to their C counterpart? Shouldn't
> '%x.addr' or '%p.addr' a better naming convention? Is there anything that I
> am missing?
>

You're right that the name isn't the most accurate from a clang point of
view, redirecting to cfe-dev@ if anyone has an opinion from the clang side.

Note though that in LLVM the SSA value names are just for debugging, they
are even stripped entirely by default in a Release clang "normal" path.

-- 
Mehdi
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