[PATCH] D110257: [CFE][Codegen] Do not break the contiguity of static allocas.

Wed Sep 22 11:26:24 PDT 2021

jdoerfert added a subscriber: rnk.
jdoerfert added a comment.

In D110257#3015712 <https://reviews.llvm.org/D110257#3015712>, @jdoerfert wrote:

> In D110257#3015641 <https://reviews.llvm.org/D110257#3015641>, @hsmhsm wrote:
>
>> In D110257#3015553 <https://reviews.llvm.org/D110257#3015553>, @arsenm wrote:
>>
>>> I do think it's cleaner/more canonical IR to cluster these at the top of the block, but I don't understand this comment:
>>>
>>>> otherwise, inliner's attempt to move static allocas from callee to caller will fail,
>>>
>>> The inliner successfully moves allocas to the caller's entry block, even with addrspacecasts interspersed.
>>
>> The logic at https://github.com/llvm/llvm-project/blob/main/llvm/lib/Transforms/Utils/InlineFunction.cpp#L2093 assumes that static allocas (within callee) are contiguous.
>
> True. Even worse. It will bail if a static alloca is used as an `inalloca` argument.
> So, if you now interleave allocas that may be used in `inalloca` you also break the "canonical form". 
> I assume this hits mostly windows but still.

@rnk This might be of interest to you. Any thoughts?

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