[PATCH] D87136: [ARM][MachineOutliner] Add calls default handling.

[Sam Parker via Phabricator via llvm-commits]

samparker added inline comments.


================
Comment at: llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp:5694
+        FrameDefault(target.isThumb() ? 2 : 4),
+        SaveRestoreLROnStack(target.isThumb() ? 8 : 8) {}
 };
----------------
yroux wrote:
> samparker wrote:
> > yroux wrote:
> > > samparker wrote:
> > > > So this is the cost of the store and load, but don't we also need to consider the frame setup too?
> > > The variable NumBytesToCreateFrame is initialized to the default cost of the frame setup and then incremented by the cost of the load/store if needed
> > So I'm sorry if I'm just being a bit blind (and/or horribly confused!) But I see:
> > 
> > ```
> > unsigned NumBytesToCreateFrame = Costs.FrameDefault;
> > NumBytesToCreateFrame += Costs.SaveRestoreLROnStack;
> > ```
> > Does this really translate the the cost of inserting:
> > - a call to the outlined function.
> > - a sub to adjust the stack pointer in the outlined function.
> > - the stack store of LR.
> > - the bx lr from the outlined function.
> > - the stack restore of LR.
> > 
> > Am I missing some logic that calls SetCandidateCallInfo?
> Ok, let's look at the Default case for ARM mode:
> 
> * The cost of the call to the outlined function is handled by the setCallInfo method of a candidate, in which Cost.CallDefault is passed.
> * Then for the frame:
>   -  I used a STR_PRE_IMM which decrement SP and store LR in 4 bytes
>   - then LR and stack are restored LDR_POST_IMM which is alsor 4 bytes (so the cost of save and restore is 8)
>   - and we have the BX LR, is cost is handled by FrameDefault (4 bytes)
> 
Ah, indexed load/store! Sorry for missing that in the tests, thanks for clearing that up.


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https://reviews.llvm.org/D87136