[llvm-dev] Why this piece of LLVM IR isn't optimized out at O3

[David Blaikie via llvm-dev]

Hard to say without the complete IR (though minimizing it first before
sharing would be helpful - and might show you what's important along the
way).


On Tue, Aug 13, 2019 at 1:05 AM Zhang via llvm-dev <llvm-dev at lists.llvm.org>
wrote:

> ```
>   %218 = call %struct._object* @PyObject_GetAttr(%struct._object* %216,
> %struct._object* %217)
>   store %struct._object* %218, %struct._object** %26, align 8
>   %219 = load %struct._object*, %struct._object** %26, align 8
> ```
> It seems to me that %219 should't exist at all.
> For that %store, there is only one instruction loading from it later on
> (although in a different succeeding block) so I'd assume it should get
> optimized too, leaving an empty unreferenced alloca at the beginning of the
> Entry Block. But running opt src.bc -S -o opt.ll -O3 didn't change them.
>
> What did I misunderstand here?
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