The PPC MFCR instruction implicitly uses all 8 of the CR

registers.  Currently it is not so marked, which leads to
VCMPEQ instructions that feed into it getting deleted.
If it is so marked, local RA complains about this sequence:
 vreg = MCRF  CR0
 MFCR  <kill of whatever preg got assigned to vreg>
All current uses of this instruction are only interested in
one of the 8 CR registers, so redefine MFCR to be a normal
unary instruction with a CR input (which is emitted only as
a comment).  That avoids all problems.  7739628.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@104238 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 6 deletions

diff --git a/lib/Target/PowerPC/PPCInstrInfo.td b/lib/Target/PowerPC/PPCInstrInfo.td
index 4d153c4..63b4581 100644
--- a/lib/Target/PowerPC/PPCInstrInfo.td
+++ b/lib/Target/PowerPC/PPCInstrInfo.td
@@ -1117,14 +1117,17 @@ def MFVRSAVE : XFXForm_1_ext<31, 339, 256, (outs GPRC:$rT), (ins),
 def MTCRF : XFXForm_5<31, 144, (outs), (ins crbitm:$FXM, GPRC:$rS),
                       "mtcrf $FXM, $rS", BrMCRX>,
             PPC970_MicroCode, PPC970_Unit_CRU;
-// FIXME:  this Uses all the CR registers.  Marking it as such is 
-// necessary for DeadMachineInstructionElim to do the right thing.
-// However, marking it also exposes PR 2964, and causes crashes in
-// the Local RA because it doesn't like this sequence:
+
+// This is a pseudo for MFCR, which implicitly uses all 8 of its subregisters;
+// declaring that here gives the local register allocator problems with this:
 //  vreg = MCRF  CR0
 //  MFCR  <kill of whatever preg got assigned to vreg>
-// For now DeadMachineInstructionElim is turned off, so don't do the marking.
-def MFCR  : XFXForm_3<31, 19, (outs GPRC:$rT), (ins), "mfcr $rT", SprMFCR>,
+// while not declaring it breaks DeadMachineInstructionElimination.
+// As it turns out, in all cases where we currently use this,
+// we're only interested in one subregister of it.  Represent this in the
+// instruction to keep the register allocator from becoming confused.
+def MFCRpseud: XFXForm_3<31, 19, (outs GPRC:$rT), (ins crbitm:$FXM),
+                       "mfcr $rT ${:comment} $FXM", SprMFCR>,
             PPC970_MicroCode, PPC970_Unit_CRU;
 def MFOCRF: XFXForm_5a<31, 19, (outs GPRC:$rT), (ins crbitm:$FXM),
                        "mfcr $rT, $FXM", SprMFCR>,