llvm dev - Jul 2021 - Querying IRTranslator value mapping results

Hi llvm-dev,

I have the following problem - I want to generate a target instruction
which denotes LLVM type of a value and its argument should be the value's
vreg. Correct me if I'm wrong, the only stage I can do that at is
IRTranslator since later we don't have any access to LLVM values at all,
but IRTranslator's VMap is private and no other way to access such info
exists.

In this review https://reviews.llvm.org/D101538 it was already discussed
that overriding translate() methods is not good enough, can you suggest
other ways of coping with that?

I thought about extending GISelObserver with a new event, something like
'VRegCreated(Value*,VReg), what do you think? Or perhaps some TTI hook
called within translate/getOrCreateVRegs.

I've tried approaches with target pseudo intrinsics and extra IR passes,
but still everything depends on missing the external (relatively to the
IRTranslator) way to obtain the info about Value->Vreg mapping.

Thanks,
Alex
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Gentle ping

Thanks,
Alex

From: Aleksandr Bezzubikov <zuban32s at gmail.com>
Sent: Monday, July 12, 2021 5:25 PM
To: llvm-dev at lists.llvm.org; quentin.colombet at gmail.com; jay.foad at
gmail.com; Matthew.Arsenault at amd.com
Cc: Bezzubikov, Aleksandr <aleksandr.bezzubikov at intel.com>
Subject: Querying IRTranslator value mapping results

Hi llvm-dev,


I have the following problem - I want to generate a target instruction which
denotes LLVM type of a value and its argument should be the value's vreg.
Correct me if I'm wrong, the only stage I can do that at is IRTranslator
since later we don't have any access to LLVM values at all, but
IRTranslator's VMap is private and no other way to access such info exists.

In this review https://reviews.llvm.org/D101538 it was already discussed that
overriding translate() methods is not good enough, can you suggest other ways of
coping with that?

I thought about extending GISelObserver with a new event, something like
'VRegCreated(Value*,VReg), what do you think? Or perhaps some TTI hook
called within translate/getOrCreateVRegs.

I've tried approaches with target pseudo intrinsics and extra IR passes, but
still everything depends on missing the external (relatively to the
IRTranslator) way to obtain the info about Value->Vreg mapping.

Thanks,
Alex
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