llvm dev - Jul 2020 - Selection DAG chain question

> Chain doesn't guarantee that operations on parallel chains don't
get
interleaved

This would be a sequential chain...
> This is the case for all operations expanded as library calls
I think their originating node already has a chain (i.e. mem operand or
side effect in llvm-ir). My case is a arithmetic node without ordering
constraints (divrem) getting lowered into sth that _does_ have ordering
constraints. I first thought it is very straight forward, turns out it is
not a common case. My current WA will be to code prepare into intrinsics
with side-effects. I was wondering if that's really necessary..

Thanks for the input

On Thu, Jul 16, 2020 at 11:21 AM Matt Arsenault <arsenm2 at gmail.com>
wrote:
>
>
> On Jul 16, 2020, at 14:10, Hendrik Greving via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> I scanned other architectures, haven't found an example where somebody
> creates a chain out of thin air. Do you know any?
>
>
>
> This is the case for all operations expanded as library calls. The call
> sequence involves a chain. One of the AMDGPU fdiv expansions also
> introduces a side effecting mode switch with a chain
>
> -Matt
>
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> On Jul 16, 2020, at 14:47, Hendrik Greving <hgreving at google.com>
wrote:
> 
> I think their originating node already has a chain (i.e. mem operand or
side effect in llvm-ir)

No, non-sideeffecting operations can be legalized as compiler-rt calls

-Matt
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> No, non-sideeffecting operations can be legalized as compiler-rt calls
Right, but not as "regular" nodes with side-effects? I guess you could
search and analyze the DAG manually but that seems hacky. Maybe something
that one day LLVM could support natively.

On Thu, Jul 16, 2020 at 11:55 AM Matt Arsenault <arsenm2 at gmail.com>
wrote:
>
>
> On Jul 16, 2020, at 14:47, Hendrik Greving <hgreving at google.com>
wrote:
>
> I think their originating node already has a chain (i.e. mem operand or
> side effect in llvm-ir)
>
>
>
> No, non-sideeffecting operations can be legalized as compiler-rt calls
>
> -Matt
>
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