[llvm-commits] [llvm] r56911 - in /llvm/trunk/lib/Target/X86: X86Instr64bit.td X86InstrInfo.td

[Dan Gohman]

On Oct 1, 2008, at 9:46 AM, Evan Cheng wrote:

> Hmmm. There could be more bugs of the kind. Any instruction that
> touches a non-allocatable register should not be deleted.

The problem with this approach is EFLAGS. It's non-allocatable,
but treating it as always live means that DCE doesn't end up
eliminating almost anything.

> If your DCE
> is not checking that, then we need to make sure all instructions that
> touch esp, etc. should mark these uses.

All the PUSHes and POPs are already marked, as are
ADJCALLSTACKDOWN, and ADJCALLSTACKUP.

Not all the terminator instructions are marked, but I guess it's
implicitly assumed that ESP/RSP are always live-out.
DeadMachineInstructionElim currently assumes that all non-allocatable
registers are live-out, so it currently doesn't care.

Are there others?

Dan