[LLVMdev] Canonicalization of ptrtoint/inttoptr and getelementptr

[Reid Kleckner]

On Mon, Sep 8, 2014 at 4:22 PM, Dan Gohman <dan433584 at gmail.com> wrote:

> It looks a little silly to say this in the case of the integer constant 5,
> and there are some semantic gray areas around extra-VM allocation, but the
> same thing happens if the add were adding a dynamic integer value, and then
> it's difficult to find a way to separate that case from the constant 5 case.
>

Could we say that constant integers have no objects associated with them?
If so, we need a way to bless constant integers that *do* refer to real
objects, such as ASan's shadow memory base.

Then you should be able to take something like add a phi of constant ints
to an inttoptr and transform that to a GEP, without explicitly calling out
constant integers.


> In any case, the general advice is that people should prefer to use
> getelementptr to begin with. LLVM's own optimizers were converted to use
> getelementptr instead of ptrtoint+add+inttoptr even when they have to do
> raw byte arithmetic.
>

I'm guessing the IR comes from C++ code that subtracts pointers, so it'd be
good if we could figure this out.
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