Fix some scavenger performance issues.

- Don't call malloc+free in the very hot forward().
- Don't call isTiedToDefOperand().
- Don't create BitVector temporaries.
- Merge DeadRegs into KillRegs.
- Eliminate the early clobber checks, they were irrelevant to scavenging.
- Remove unnecessary code from -Asserts builds.

This speeds up ARM PEI by 3.4x and overall llc -O0 codegen time by 11%.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@149189 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/RegisterScavenging.h

@@ -68,6 +68,10 @@ class RegScavenger {
   /// available, unset means the register is currently being used.
   BitVector RegsAvailable;
 
+  // These BitVectors are only used internally to forward(). They are members
+  // to avoid frequent reallocations.
+  BitVector KillRegs, DefRegs;
+
 public:
   RegScavenger()
     : MBB(NULL), NumPhysRegs(0), Tracking(false),
@@ -139,7 +143,7 @@ private:
   /// setUsed / setUnused - Mark the state of one or a number of registers.
   ///
   void setUsed(BitVector &Regs) {
-    RegsAvailable &= ~Regs;
+    RegsAvailable.reset(Regs);
   }
   void setUnused(BitVector &Regs) {
     RegsAvailable |= Regs;
@@ -148,9 +152,6 @@ private:
   /// Add Reg and all its sub-registers to BV.
   void addRegWithSubRegs(BitVector &BV, unsigned Reg);
 
-  /// Add Reg and its aliases to BV.
-  void addRegWithAliases(BitVector &BV, unsigned Reg);
-
   /// findSurvivorReg - Return the candidate register that is unused for the
   /// longest after StartMI. UseMI is set to the instruction where the search
   /// stopped.

lib/CodeGen/RegisterScavenging.cpp

@@ -90,6 +90,8 @@ void RegScavenger::enterBasicBlock(MachineBasicBlock *mbb) {
   if (!MBB) {
     NumPhysRegs = TRI->getNumRegs();
     RegsAvailable.resize(NumPhysRegs);
+    KillRegs.resize(NumPhysRegs);
+    DefRegs.resize(NumPhysRegs);
 
     // Create reserved registers bitvector.
     ReservedRegs = TRI->getReservedRegs(MF);
@@ -114,12 +116,6 @@ void RegScavenger::addRegWithSubRegs(BitVector &BV, unsigned Reg) {
     BV.set(*R);
 }
 
-void RegScavenger::addRegWithAliases(BitVector &BV, unsigned Reg) {
-  BV.set(Reg);
-  for (const unsigned *R = TRI->getAliasSet(Reg); *R; R++)
-    BV.set(*R);
-}
-
 void RegScavenger::forward() {
   // Move ptr forward.
   if (!Tracking) {
@@ -148,10 +144,8 @@ void RegScavenger::forward() {
   // predicated, conservatively assume "kill" markers do not actually kill the
   // register. Similarly ignores "dead" markers.
   bool isPred = TII->isPredicated(MI);
-  BitVector EarlyClobberRegs(NumPhysRegs);
+  KillRegs.reset();
-  BitVector KillRegs(NumPhysRegs);
+  DefRegs.reset();
-  BitVector DefRegs(NumPhysRegs);
-  BitVector DeadRegs(NumPhysRegs);
   for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
     const MachineOperand &MO = MI->getOperand(i);
     if (!MO.isReg())
@@ -164,21 +158,19 @@ void RegScavenger::forward() {
       // Ignore undef uses.
       if (MO.isUndef())
         continue;
-      // Two-address operands implicitly kill.
+      if (!isPred && MO.isKill())
-      if (!isPred && (MO.isKill() || MI->isRegTiedToDefOperand(i)))
         addRegWithSubRegs(KillRegs, Reg);
     } else {
       assert(MO.isDef());
       if (!isPred && MO.isDead())
-        addRegWithSubRegs(DeadRegs, Reg);
+        addRegWithSubRegs(KillRegs, Reg);
       else
         addRegWithSubRegs(DefRegs, Reg);
-      if (MO.isEarlyClobber())
-        addRegWithAliases(EarlyClobberRegs, Reg);
     }
   }
 
   // Verify uses and defs.
+#ifndef NDEBUG
   for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
     const MachineOperand &MO = MI->getOperand(i);
     if (!MO.isReg())
@@ -205,16 +197,12 @@ void RegScavenger::forward() {
             SubUsed = true;
             break;
           }
-#ifndef NDEBUG
         if (!SubUsed) {
           MBB->getParent()->verify(NULL, "In Register Scavenger");
           llvm_unreachable("Using an undefined register!");
         }
-#endif
         (void)SubUsed;
       }
-      assert((!EarlyClobberRegs.test(Reg) || MI->isRegTiedToDefOperand(i)) &&
-             "Using an early clobbered register!");
     } else {
       assert(MO.isDef());
 #if 0
@@ -226,10 +214,10 @@ void RegScavenger::forward() {
 #endif
     }
   }
+#endif // NDEBUG
 
   // Commit the changes.
   setUnused(KillRegs);
-  setUnused(DeadRegs);
   setUsed(DefRegs);
 }