[PATCH] D53878: [AArch64] Mark condition flags as clobbered when calling __chkstk

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

For both cases; the "blr x16" both uses and clobbers x16, so it needs two operands to represent that.  `.addReg(AArch64::X16, RegState::Implicit | RegState::Define | RegState::Dead)` is correct (just like you used for NZCV).

"RegState::Define" means it's a definition, rather than a use.  RegState::Implicit means that it's not one of the explicit inputs or outputs listed in the instruction description.  RegState::Dead and RegState::Kill are optimization hints; a dead definition is never used, and a "kill" use is the last use of a definition.

> (Not that I know what really would assume these registers to have any sensible value here, as this is emitted in the prologue of a function.)

In theory, if unwind tables are disabled, some code after the prologue could get rescheduled into the prologue.

> I guess AArch64 COFF linkers in general could support range extension thunks, although I don't know if link.exe does - lld doesn't at least.

I would be surprised if link.exe doesn't support it, given it supports the equivalent for 32-bit ARM.


Repository:
  rL LLVM

https://reviews.llvm.org/D53878