[LLVMdev] The target independence of IR

[Kuperstein, Michael M]

Hi Hao,

You are right, the IR is not “target independent” in the strict sense.

There’s a fairly old post that explains this (amongst other things) in detail:
http://lists.cs.uiuc.edu/pipermail/llvmdev/2011-October/043719.html
x86_fp80 is just one example of this.

It is kind-of-possible to restrict LLVM IR to be sort-of-target-independent (look up Portable Native Client and SPIR for details), but an arbitrary IR file generated by a front-end that had target X in mind is not guaranteed to work as you’d expect if you use backend Y.

Michael

From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Hao Wang
Sent: Tuesday, December 09, 2014 09:33
To: llvmdev at cs.uiuc.edu
Subject: [LLVMdev] The target independence of IR

Hi,

Can anyone help me understand that LLVM IR has "target independence" ?

1. When we talk about "target", we mean something like Instruction Set Architecture ?

2. The front-end may generate IR code such as x86_fp80, so the IR is actually not fully target-independent? It contains information about the target, and the front-end should also be aware of this?

Thank you!

Hao
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