[PowerPC][NFC] Small cleanup to restore CR field code in PPCFrameLowering.

Skip the loop over the CalleSavedInfos in 'restoreCalleeSavedRegisters' when
the register is a CR field and we are not targeting 32-bit ELF. This is safe
because:
1) The helper function 'restoreCRs' returns if the target is not 32-bit ELF,
   making all the code in the loop related to CR fields dead for every other
   subtarget. This code is only called on ELF right now, but the patch
   to extend it for AIX also needs to skip 'restoreCRs'.
2) The loop will not otherwise modify the iterator, so the iterator
   manipulations at the bottom of the loop end up setting 'I' to its
   current value.

This simplifciation allows us to remove one argument from 'restoreCRs'.

Also add a helper function to determine if a register is one of the
callee saved condition register fields.

Author: mandlebug

llvm/lib/Target/PowerPC/PPCFrameLowering.cpp

@@ -2253,28 +2253,22 @@ bool PPCFrameLowering::spillCalleeSavedRegisters(
   return true;
 }
 
-static void restoreCRs(bool isPPC64, bool is31, bool CR2Spilled,
-                       bool CR3Spilled, bool CR4Spilled, MachineBasicBlock &MBB,
+static void restoreCRs(bool is31, bool CR2Spilled, bool CR3Spilled,
+                       bool CR4Spilled, MachineBasicBlock &MBB,
                        MachineBasicBlock::iterator MI,
                        ArrayRef<CalleeSavedInfo> CSI, unsigned CSIIndex) {
 
   MachineFunction *MF = MBB.getParent();
   const PPCInstrInfo &TII = *MF->getSubtarget<PPCSubtarget>().getInstrInfo();
   DebugLoc DL;
-  unsigned RestoreOp, MoveReg;
+  unsigned MoveReg = PPC::R12;
 
-  if (isPPC64)
-    // This is handled during epilogue generation.
-    return;
-  else {
-    // 32-bit:  FP-relative
-    MBB.insert(MI, addFrameReference(BuildMI(*MF, DL, TII.get(PPC::LWZ),
-                                             PPC::R12),
-                                     CSI[CSIIndex].getFrameIdx()));
-    RestoreOp = PPC::MTOCRF;
-    MoveReg = PPC::R12;
-  }
+  // 32-bit:  FP-relative
+  MBB.insert(MI,
+             addFrameReference(BuildMI(*MF, DL, TII.get(PPC::LWZ), MoveReg),
+                               CSI[CSIIndex].getFrameIdx()));
 
+  unsigned RestoreOp = PPC::MTOCRF;
   if (CR2Spilled)
     MBB.insert(MI, BuildMI(*MF, DL, TII.get(RestoreOp), PPC::CR2)
                .addReg(MoveReg, getKillRegState(!CR3Spilled && !CR4Spilled)));
@@ -2327,6 +2321,10 @@ eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
   return MBB.erase(I);
 }
 
+static bool isCalleeSavedCR(unsigned Reg) {
+  return PPC::CR2 == Reg || Reg == PPC::CR3 || Reg == PPC::CR4;
+}
+
 bool
 PPCFrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
                                         MachineBasicBlock::iterator MI,
@@ -2365,6 +2363,11 @@ PPCFrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
     if ((Reg == PPC::X2 || Reg == PPC::R2) && MustSaveTOC)
       continue;
 
+    // Restore of callee saved condition register field is handled during
+    // epilogue insertion.
+    if (isCalleeSavedCR(Reg) && !Subtarget.is32BitELFABI())
+      continue;
+
     if (Reg == PPC::CR2) {
       CR2Spilled = true;
       // The spill slot is associated only with CR2, which is the
@@ -2380,12 +2383,10 @@ PPCFrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
     } else {
       // When we first encounter a non-CR register after seeing at
       // least one CR register, restore all spilled CRs together.
-      if ((CR2Spilled || CR3Spilled || CR4Spilled)
-          && !(PPC::CR2 <= Reg && Reg <= PPC::CR4)) {
+      if (CR2Spilled || CR3Spilled || CR4Spilled) {
         bool is31 = needsFP(*MF);
-        restoreCRs(Subtarget.isPPC64(), is31,
-                   CR2Spilled, CR3Spilled, CR4Spilled,
-                   MBB, I, CSI, CSIIndex);
+        restoreCRs(is31, CR2Spilled, CR3Spilled, CR4Spilled, MBB, I, CSI,
+                   CSIIndex);
         CR2Spilled = CR3Spilled = CR4Spilled = false;
       }
 
@@ -2423,9 +2424,10 @@ PPCFrameLowering::restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
 
   // If we haven't yet spilled the CRs, do so now.
   if (CR2Spilled || CR3Spilled || CR4Spilled) {
+    assert(Subtarget.is32BitELFABI() &&
+           "Only set CR[2|3|4]Spilled on 32-bit SVR4.");
     bool is31 = needsFP(*MF);
-    restoreCRs(Subtarget.isPPC64(), is31, CR2Spilled, CR3Spilled, CR4Spilled,
-               MBB, I, CSI, CSIIndex);
+    restoreCRs(is31, CR2Spilled, CR3Spilled, CR4Spilled, MBB, I, CSI, CSIIndex);
   }
 
   return true;