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

5 files changed, 24 insertions, 21 deletions

diff --git a/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index 3d9f8aa..00eebb8 100644
--- a/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -712,8 +712,9 @@ SDNode *PPCDAGToDAGISel::SelectSETCC(SDNode *N) {
   if (PPCSubTarget.isGigaProcessor() && OtherCondIdx == -1)
     IntCR = SDValue(CurDAG->getMachineNode(PPC::MFOCRF, dl, MVT::i32, CR7Reg,
                                            CCReg), 0);
-  else
-    IntCR = SDValue(CurDAG->getMachineNode(PPC::MFCR, dl, MVT::i32, CCReg), 0);
+ else
+    IntCR = SDValue(CurDAG->getMachineNode(PPC::MFCRpseud, dl, MVT::i32,
+                                           CR7Reg, CCReg), 0);
   
   SDValue Ops[] = { IntCR, getI32Imm((32-(3-Idx)) & 31),
                       getI32Imm(31), getI32Imm(31) };
@@ -848,7 +849,8 @@ SDNode *PPCDAGToDAGISel::Select(SDNode *N) {
       return CurDAG->getMachineNode(PPC::MFOCRF, dl, MVT::i32,
                                     N->getOperand(0), InFlag);
     else
-      return CurDAG->getMachineNode(PPC::MFCR, dl, MVT::i32, InFlag);
+      return CurDAG->getMachineNode(PPC::MFCRpseud, dl, MVT::i32,
+                                    N->getOperand(0), InFlag);
   }
     
   case ISD::SDIV: {
diff --git a/lib/Target/PowerPC/PPCISelLowering.h b/lib/Target/PowerPC/PPCISelLowering.h
index 1d05f3d..6dcaf1e 100644
--- a/lib/Target/PowerPC/PPCISelLowering.h
+++ b/lib/Target/PowerPC/PPCISelLowering.h
@@ -111,9 +111,10 @@ namespace llvm {
       /// Return with a flag operand, matched by 'blr'
       RET_FLAG,
       
-      /// R32 = MFCR(CRREG, INFLAG) - Represents the MFCR/MFOCRF instructions.
-      /// This copies the bits corresponding to the specified CRREG into the
-      /// resultant GPR.  Bits corresponding to other CR regs are undefined.
+      /// R32 = MFCR(CRREG, INFLAG) - Represents the MFCRpseud/MFOCRF
+      /// instructions.  This copies the bits corresponding to the specified
+      /// CRREG into the resultant GPR.  Bits corresponding to other CR regs
+      /// are undefined.
       MFCR,
 
       /// RESVEC = VCMP(LHS, RHS, OPC) - Represents one of the altivec VCMP*
diff --git a/lib/Target/PowerPC/PPCInstrInfo.cpp b/lib/Target/PowerPC/PPCInstrInfo.cpp
index ae95ae4..1b7a778 100644
--- a/lib/Target/PowerPC/PPCInstrInfo.cpp
+++ b/lib/Target/PowerPC/PPCInstrInfo.cpp
@@ -442,7 +442,8 @@ PPCInstrInfo::StoreRegToStackSlot(MachineFunction &MF,
       // issue a MFCR to save all of the CRBits.
       unsigned ScratchReg = TM.getSubtargetImpl()->isDarwinABI() ? 
                                                            PPC::R2 : PPC::R0;
-      NewMIs.push_back(BuildMI(MF, DL, get(PPC::MFCR), ScratchReg));
+      NewMIs.push_back(BuildMI(MF, DL, get(PPC::MFCRpseud), ScratchReg)
+                               .addReg(SrcReg, getKillRegState(isKill)));
     
       // If the saved register wasn't CR0, shift the bits left so that they are
       // in CR0's slot.
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>,
diff --git a/lib/Target/PowerPC/PPCRegisterInfo.cpp b/lib/Target/PowerPC/PPCRegisterInfo.cpp
index 0bccf15..0ff852c 100644
--- a/lib/Target/PowerPC/PPCRegisterInfo.cpp
+++ b/lib/Target/PowerPC/PPCRegisterInfo.cpp
@@ -689,19 +689,15 @@ void PPCRegisterInfo::lowerCRSpilling(MachineBasicBlock::iterator II,
   const TargetRegisterClass *GPRC = &PPC::GPRCRegClass;
   const TargetRegisterClass *RC = Subtarget.isPPC64() ? G8RC : GPRC;
   unsigned Reg = findScratchRegister(II, RS, RC, SPAdj);
+  unsigned SrcReg = MI.getOperand(0).getReg();
 
   // We need to store the CR in the low 4-bits of the saved value. First, issue
-  // an MFCR to save all of the CRBits. Add an implicit kill of the CR.
-  if (!MI.getOperand(0).isKill())
-    BuildMI(MBB, II, dl, TII.get(PPC::MFCR), Reg);
-  else
-    // Implicitly kill the CR register.
-    BuildMI(MBB, II, dl, TII.get(PPC::MFCR), Reg)
-      .addReg(MI.getOperand(0).getReg(), RegState::ImplicitKill);
+  // an MFCRpsued to save all of the CRBits and, if needed, kill the SrcReg.
+  BuildMI(MBB, II, dl, TII.get(PPC::MFCRpseud), Reg)
+          .addReg(SrcReg, getKillRegState(MI.getOperand(0).isKill()));
     
   // If the saved register wasn't CR0, shift the bits left so that they are in
   // CR0's slot.
-  unsigned SrcReg = MI.getOperand(0).getReg();
   if (SrcReg != PPC::CR0)
     // rlwinm rA, rA, ShiftBits, 0, 31.
     BuildMI(MBB, II, dl, TII.get(PPC::RLWINM), Reg)