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mipsseiseldagtodag
2017 Dec 24
4
Canonical way to handle zero registers?
...hineFunction to perform
> ISEL, then post processing the output by finding the cases where -1 is
> synthesized then used and replacing the uses
> of the synthesized -1 with the register wired to -1?
>
> The MIPS backend takes this approach for dealing with the zero register,
> see MipSEISelDAGToDAG.cpp for reference.
>
> Thanks,
> Simon
> ------------------------------
> *From:* llvm-dev [llvm-dev-bounces at lists.llvm.org] on behalf of Sean
> Silva via llvm-dev [llvm-dev at lists.llvm.org]
> *Sent:* Friday, December 22, 2017 5:22 AM
> *To:* llvm-dev
> *Subject:* [l...
2017 Dec 22
4
Canonical way to handle zero registers?
I looked around the codebase and didn't see anything that obviously looked
like the natural place to turn constant zero immediates into zero-registers
(i.e. registers that always return zero when read). Right now we are
expanding them in ISelLowering::LowerOperation but that seems too early.
The specific issue I'm hitting is that we have a register that reads as -1
and so when we replace