[cfe-dev] Question on "phi-node-folding-threshold"

[Craig Topper via cfe-dev]

You can probably force it from Clang::RenderTargetOptions. Various targets
force some -mllvm options from there.

~Craig


On Wed, Sep 18, 2019 at 10:05 PM Joan Lluch <joan.lluch at icloud.com> wrote:

> Hi Craig,
>
> This worked. Thank you very much.
>
> Is there a way to specify this by default for a particular target?. I
> implemented a LLVM backend and added all the required code so that Clang
> recognises it as a target, but I’m unsure about how to deal with this
> particularly. Ideally, Clang should use ‘phi-node-folding-threshold=1’
> automatically when my target is specified. Any suggestions are appreciated.
>
> Thanks again.
>
> John
>
>
> On 18 Sep 2019, at 08:34, Craig Topper <craig.topper at gmail.com> wrote:
>
> You can set it on the command line by doing "clang -mllvm
> -phi-node-folding-threshold=1”  The -mllvm tells clang to pass the next
> argument through to the command line system used by IR passes.
>
> ~Craig
>
>
> On Tue, Sep 17, 2019 at 11:05 PM Joan Lluch via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
>> Hi All,
>>
>> For a custom backend I’m developing, where jumps are not particularly
>> expensive, I want to reduce the phi-node-folding-threshold attribute
>> value from the default 2 to just 1, as it produces better code in my case.
>>
>> I first tried to set the attribute as a clang command line option, but it
>> does not seem to be available. ( I tried “clang
>>  -phi-node-folding-threshold=1” but this returns an “unknown argument”
>> error)
>>
>> However, it works as intended if I replace the default value by hard
>> coding in it in SimplifyCFG.cpp and recompiling clang
>>
>>  My question is, Is there a way to set that attribute to a different
>> value for a specific target?. Or at least to set it on the command line?
>>
>> Thanks in advance
>>
>> John
>> _______________________________________________
>> cfe-dev mailing list
>> cfe-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>
>
>
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