[PATCH] Changing the Back-end when Target Options Change

[Bill Wendling]

On Jun 20, 2013, at 6:48 AM, "Du Toit, Stefanus" <stefanus.du.toit at intel.com> wrote:

> Hi Bill,
> 
> From:  Bill Wendling <wendling at apple.com>
>> For those not interested in slugging their way through a ton of
>> refactoring code, here's a cleaner patch.
>> 
>> The executive summary:
>> 
>> This regenerates the TargetMachine object if the any of the values in
>> TargetOptions changes. The regeneration is recursive, because creating
>> TargetMachine pretty much creates all of the other back-end objects that
>> are needed for code generation.
> 
> You could use the "curiously recurring template pattern" and add an
> instance of a class template in the middle of the inheritance hierarchy,
> e.g. something alone the lines of:
> 
> template<typename Derived>
> class TargetMachineHelper : public TargetMachine {
>  TargetMachine *
>  regenerateWithOptionsImpl(const TargetOptions &Opts,
>                            Reloc::Model RM,
>                            CodeModel::Model CM,
>                            CodeGenOpt::Level OptLvl,
>                            std::string &targetTriple,
>                            std::string &targetCPU,
>                            std::string &targetFS) {
>    TargetPassConfig *TPC = PassConfig;
> 
>    this->~Derived();
>    Derived *NewTM = new (this)
>      Derived(TheTarget, targetTriple, targetCPU, targetFS,
>              Opts, RM, CM, OptLvl);
> 
>    if (TPC)
>      NewTM->PassConfig = TPC->regenerateWithTargetMachine(NewTM);
> 
>    return NewTM;
>  }
> };
> 
> // Then, for each backend, change the inheritance like so:
> 
> class MyTargetMachine : public TargetMachineHelper<MyTargetMachine> {
> // ...
> 
> (I'm sure there are errors in the above, but hopefully it gets the idea
> across)
> 
> This would remove the need to define all of these similar-looking
> functions in the backends. Should work for PassConfig too.
> 
Not a bad idea. I'll look into it. Thanks!

-bw