[PATCH] D42006: AArch64: Omit callframe setup/destroy when not necessary

[Matthias Braun via Phabricator via llvm-commits]

MatzeB added a comment.

In https://reviews.llvm.org/D42006#979433, @efriedma wrote:

> Various backends handle this situation different ways... ARM emits an inline loop, x86  and x86 emit an inline loop rather than a call.  PowerPC has a utility createMemcpyOutsideCallSeq which avoids nesting.  And this would introduce, essentially, a third way to handle it.  We should probably settle on one solution, if possible.


True, I could look into whether this simple solution would avoid the special case on PowerPC as well; but let's do that in a separate patch.
I'm not sure I want to change ARM/X86 from an inline loop to memcpy as it changes the performance characteristics (slightly slower for small sizes, faster for big sizes).

In any case I found this change desirable independently of it fixing the nesting issue.

> Some target-independent code has special handling for callframe operations... but I guess most of the handling isn't necessary?  Does a call without call frame setup instructions correctly disable the red zone?

AArch64FrameLowering::canUseRedZone() checks for MachineFrameInfo::hasCalls() which is set based on MCInstructions having a Call flag set not based of the stackframe setup (you can grep for `setHasCalls(true)` if you are interested).


Repository:
  rL LLVM

https://reviews.llvm.org/D42006