[PowerPC] Always use mfocrf if available

When accessing just a single CR register, it is always preferable to
use mfocrf instead of mfcr, if the former is available on the CPU.

Current code makes that distinction in many, but not all places
where a single CR register value is retrieved.  One missing
location is PPCRegisterInfo::lowerCRSpilling.

To fix this and make this simpler in the future, this patch changes
the bulk of the back-end to always assume mfocrf is available and
simply generate it when needed.

On machines that actually do not support mfocrf, the instruction
is replaced by mfcr at the very end, in EmitInstruction.

This has the additional benefit that we no longer need the
MFCRpseud hack, since before EmitInstruction we always have
a MFOCRF instruction pattern, which already models data flow
as required.

The patch also adds the MFOCRF8 version of the instruction,
which was missing so far.

Except for the PPCRegisterInfo::lowerCRSpilling case, no change
in generated code intended.

llvm-svn: 185556

1 files changed, 1 insertions, 17 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.td b/llvm/lib/Target/PowerPC/PPCInstrInfo.td
index 93208582312..e52adeeb29d 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.td
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.td
@@ -1902,30 +1902,14 @@ def MTCRF : XFXForm_5<31, 144, (outs crbitm:$FXM), (ins gprc:$rS),
                       "mtcrf $FXM, $rS", BrMCRX>,
             PPC970_MicroCode, PPC970_Unit_CRU;
 
-// This is a pseudo for MFCR, which implicitly uses all 8 of its subregisters;
-// declaring that here gives the local register allocator problems with this:
-//  vreg = MCRF  CR0
-//  MFCR  <kill of whatever preg got assigned to vreg>
-// while not declaring it breaks DeadMachineInstructionElimination.
-// As it turns out, in all cases where we currently use this,
-// we're only interested in one subregister of it.  Represent this in the
-// instruction to keep the register allocator from becoming confused.
-//
-// FIXME: Make this a real Pseudo instruction when the JIT switches to MC.
-let isCodeGenOnly = 1 in
-def MFCRpseud: XFXForm_3<31, 19, (outs gprc:$rT), (ins crbitm:$FXM),
-                       "#MFCRpseud", SprMFCR>,
-            PPC970_MicroCode, PPC970_Unit_CRU;
-
 def MFOCRF: XFXForm_5a<31, 19, (outs gprc:$rT), (ins crbitm:$FXM),
                        "mfocrf $rT, $FXM", SprMFCR>,
             PPC970_DGroup_First, PPC970_Unit_CRU;
-} // neverHasSideEffects = 1
 
-let neverHasSideEffects = 1 in
 def MFCR : XFXForm_3<31, 19, (outs gprc:$rT), (ins),
                      "mfcr $rT", SprMFCR>,
                      PPC970_MicroCode, PPC970_Unit_CRU;
+} // neverHasSideEffects = 1
 
 // Pseudo instruction to perform FADD in round-to-zero mode.
 let usesCustomInserter = 1, Uses = [RM] in {