Simplify RegScavenger::FindUnusedReg.

- Drop the Candidates argument and fix all callers. Now that RegScavenger
  tracks available registers accurately, there is no need to restict the
  search.
- Make sure that no aliases of the found register are in use. This was a potential bug.

llvm-svn: 79369

include/llvm/CodeGen/RegisterScavenging.h

@@ -98,15 +98,9 @@ public:
   /// getRegsUsed - return all registers currently in use in used.
   void getRegsUsed(BitVector &used, bool includeReserved);
 
-  /// FindUnusedReg - Find a unused register of the specified register class
-  /// from the specified set of registers. It return 0 is none is found.
-  unsigned FindUnusedReg(const TargetRegisterClass *RegClass,
-                         const BitVector &Candidates) const;
-
   /// FindUnusedReg - Find a unused register of the specified register class.
-  /// Exclude callee saved registers if directed. It return 0 is none is found.
-  unsigned FindUnusedReg(const TargetRegisterClass *RegClass,
-                         bool ExCalleeSaved = false) const;
+  /// Return 0 if none is found.
+  unsigned FindUnusedReg(const TargetRegisterClass *RegClass) const;
 
   /// setScavengingFrameIndex / getScavengingFrameIndex - accessor and setter of
   /// ScavengingFrameIndex.

lib/CodeGen/RegisterScavenging.cpp

@@ -248,36 +248,12 @@ static void CreateRegClassMask(const TargetRegisterClass *RC, BitVector &Mask) {
     Mask.set(*I);
 }
 
-unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RegClass,
-                                     const BitVector &Candidates) const {
-  // Mask off the registers which are not in the TargetRegisterClass.
-  BitVector RegsAvailableCopy(NumPhysRegs, false);
-  CreateRegClassMask(RegClass, RegsAvailableCopy);
-  RegsAvailableCopy &= RegsAvailable;
-
-  // Restrict the search to candidates.
-  RegsAvailableCopy &= Candidates;
-
-  // Returns the first unused (bit is set) register, or 0 is none is found.
-  int Reg = RegsAvailableCopy.find_first();
-  return (Reg == -1) ? 0 : Reg;
-}
-
-unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RegClass,
-                                     bool ExCalleeSaved) const {
-  // Mask off the registers which are not in the TargetRegisterClass.
-  BitVector RegsAvailableCopy(NumPhysRegs, false);
-  CreateRegClassMask(RegClass, RegsAvailableCopy);
-  RegsAvailableCopy &= RegsAvailable;
-
-  // If looking for a non-callee-saved register, mask off all the callee-saved
-  // registers.
-  if (ExCalleeSaved)
-    RegsAvailableCopy &= ~CalleeSavedRegs;
-
-  // Returns the first unused (bit is set) register, or 0 is none is found.
-  int Reg = RegsAvailableCopy.find_first();
-  return (Reg == -1) ? 0 : Reg;
+unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RC) const {
+  for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end();
+       I != E; ++I)
+    if (!isAliasUsed(*I))
+      return *I;
+  return 0;
 }
 
 /// findSurvivorReg - Return the candidate register that is unused for the

lib/Target/ARM/ARMBaseRegisterInfo.cpp

@@ -1006,12 +1006,8 @@ eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
 static
 unsigned findScratchRegister(RegScavenger *RS, const TargetRegisterClass *RC,
                              ARMFunctionInfo *AFI) {
-  unsigned Reg = RS ? RS->FindUnusedReg(RC, true) : (unsigned) ARM::R12;
+  unsigned Reg = RS ? RS->FindUnusedReg(RC) : (unsigned) ARM::R12;
   assert(!AFI->isThumb1OnlyFunction());
-  if (Reg == 0)
-    // Try a already spilled CS register.
-    Reg = RS->FindUnusedReg(RC, AFI->getSpilledCSRegisters());
-
   return Reg;
 }
 

lib/Target/ARM/ARMLoadStoreOptimizer.cpp

@@ -941,12 +941,8 @@ bool ARMLoadStoreOpt::LoadStoreMultipleOpti(MachineBasicBlock &MBB) {
         // Try to find a free register to use as a new base in case it's needed.
         // First advance to the instruction just before the start of the chain.
         AdvanceRS(MBB, MemOps);
-        // Find a scratch register. Make sure it's a call clobbered register or
-        // a spilled callee-saved register.
-        unsigned Scratch = RS->FindUnusedReg(&ARM::GPRRegClass, true);
-        if (!Scratch)
-          Scratch = RS->FindUnusedReg(&ARM::GPRRegClass,
-                                      AFI->getSpilledCSRegisters());
+        // Find a scratch register.
+        unsigned Scratch = RS->FindUnusedReg(&ARM::GPRRegClass);
         // Process the load / store instructions.
         RS->forward(prior(MBBI));
 

lib/Target/Blackfin/BlackfinRegisterInfo.cpp

@@ -213,7 +213,7 @@ static unsigned findScratchRegister(MachineBasicBlock::iterator II,
                                     const TargetRegisterClass *RC,
                                     int SPAdj) {
   assert(RS && "Register scavenging must be on");
-  unsigned Reg = RS->FindUnusedReg(RC, true);
+  unsigned Reg = RS->FindUnusedReg(RC);
   if (Reg == 0)
     Reg = RS->scavengeRegister(RC, II, SPAdj);
   return Reg;

lib/Target/PowerPC/PPCRegisterInfo.cpp

@@ -527,7 +527,7 @@ static
 unsigned findScratchRegister(MachineBasicBlock::iterator II, RegScavenger *RS,
                              const TargetRegisterClass *RC, int SPAdj) {
   assert(RS && "Register scavenging must be on");
-  unsigned Reg = RS->FindUnusedReg(RC, true);
+  unsigned Reg = RS->FindUnusedReg(RC);
   // FIXME: move ARM callee-saved reg scan to target independent code, then 
   // search for already spilled CS register here.
   if (Reg == 0)