llvm dev - Oct 2021 - [RFC] Eliminating non-IR floating-point controls in the selection DAG

On Sat, 30 Oct 2021 at 16:01, Wang, Pengfei <pengfei.wang at intel.com>
wrote:
> I think the use of target option simply owe to the fact that DAG and other
> backend passes always lose the FMFs during transformation in the past.
>
Ah! That's an interesting piece of information! And exacerbates Eric's
original comment.

At which level is that information lost?
>
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SelectionDAG has many overloaded methods of “getNode”, some of which don’t need
to specify the Flags argument. This is reasonable because only FP nodes need
that. But it also easily results in losing the Flags in the FP nodes too.
Here’s an example https://reviews.llvm.org/D84518
This problem has been greatly improved since https://reviews.llvm.org/D87361
I think we have the similar problem in MIR based optimizations, but I didn’t dig
into it.

Thanks
Phoebe (Pengfei)

From: Renato Golin <rengolin at gmail.com>
Sent: Saturday, October 30, 2021 11:41 PM
To: Wang, Pengfei <pengfei.wang at intel.com>
Cc: Kaylor, Andrew <andrew.kaylor at intel.com>; Yaxun Liu <yaxun.liu
at amd.com>; Sebastian Pop <sebpop at gmail.com>; Ammarguellat, Zahira
<zahira.ammarguellat at intel.com>; Ulrich Weigand <Ulrich.Weigand at
de.ibm.com>; Ballman, Aaron <aaron.ballman at intel.com>; llvm-dev at
lists.llvm.org
Subject: Re: [llvm-dev] [RFC] Eliminating non-IR floating-point controls in the
selection DAG

On Sat, 30 Oct 2021 at 16:01, Wang, Pengfei <pengfei.wang at
intel.com<mailto:pengfei.wang at intel.com>> wrote:
I think the use of target option simply owe to the fact that DAG and other
backend passes always lose the FMFs during transformation in the past.

Ah! That's an interesting piece of information! And exacerbates Eric's
original comment.

At which level is that information lost?
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