RetroSearch Browse

Mon Jul 13 14:35:12 PDT 2020 · https://lists.llvm.org/pipermail/llvm-dev/2020-July/143368.html

You are right that itâs mostly a convenience for the front-ends. So they donât have to deal with boring things like padding and sizing things.

Otherwise it adds no semantic value. Object aliasing is not field sensitive in LLVM, so it doesnât matter. Though someone may want to add support for that in the future for languages where itâs ok to do so.

FWIW, Alive2âs GEP instruction works over bytes only (pairs of constant * %reg). Though Iâm not sure I would advocate to change LLVMâs representation.

Nuno

From: Nikita Popov
Sent: 13 July 2020 21:08
To: llvm-dev <llvm-dev at lists.llvm.org>
Subject: [llvm-dev] Why are GEPs type based?

Hi,

I've been wondering why LLVMs GEP instructions are based on types, rather than encoding the raw address calculation as a base pointer plus some scaled offsets (still in the form of a GEP, to retain provenance).

The type information does not seem particularly useful (shouldn't be used as an optimization base, because struct layouts lie), but increases the non-canonical IR space (there are many ways to encode the same GEP) and increases compile-time (optimizations need to constantly decompose GEPs, e.g. to get constant offsets).

What am I missing here?

Nikita,

Regards

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20200713/f4aed15a/attachment.html>

Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://lists.llvm.org/pipermail/llvm-dev/2020-July/143368.html below:

[llvm-dev] Why are GEPs type based?