[PATCH] D76066: [ARM][MachineOutliner] Add Machine Outliner support for ARM

[Eli Friedman via Phabricator via cfe-commits]

efriedma added inline comments.


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Comment at: llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp:5813
+  // Don't touch the link register
+  if (MI.readsRegister(ARM::LR, TRI) || MI.modifiesRegister(ARM::LR, TRI))
+    return outliner::InstrType::Illegal;
----------------
yroux wrote:
> efriedma wrote:
> > Why do you need to forbid outlining code that touches LR or SP? None of the new instructions you're generating read or clobber them.   (It might start mattering if you add support for additional forms of outlining, or Thumb1 support, but this patch has neither.)
> I agree that there is no issue with SP until we modify it, I'll move that to the right patch, for LR it is needed here, when doing thunk outlining the call to the outlined function is a BL and if an instruction uses LR in the outlined region we will have a problem.
Oh, right, we're effectively hoisting the definition of LR in thunk outlining.  Makes sense.

For tail-call outlining, we don't care about LR, but I guess it's trickier to separate out those two cases.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D76066/new/

https://reviews.llvm.org/D76066