Avoid calling TRI->getAllocatableSet in RAFast.

When compiling a program with lots of small functions like
483.xalancbmk, this makes RAFast 11% faster.

Add some comments to clarify the difference between unallocatable and
reserved registers. It's quite subtle.

The fast register allocator depends on EFLAGS' not being allocatable on
x86. That way it can completely avoid tracking liveness, and it won't
mind when there are multiple uses of a single def.

llvm-svn: 132514

1 files changed, 4 insertions, 9 deletions

diff --git a/llvm/lib/CodeGen/RegAllocFast.cpp b/llvm/lib/CodeGen/RegAllocFast.cpp
index 58739ff31d3..97652036f98 100644
--- a/llvm/lib/CodeGen/RegAllocFast.cpp
+++ b/llvm/lib/CodeGen/RegAllocFast.cpp
@@ -115,9 +115,6 @@ namespace {
     // instruction, and so cannot be allocated.
     BitVector UsedInInstr;
 
-    // Allocatable - vector of allocatable physical registers.
-    BitVector Allocatable;
-
     // SkippedInstrs - Descriptors of instructions whose clobber list was
     // ignored because all registers were spilled. It is still necessary to
     // mark all the clobbered registers as used by the function.
@@ -485,7 +482,7 @@ void RAFast::allocVirtReg(MachineInstr *MI, LiveRegEntry &LRE, unsigned Hint) {
 
   // Ignore invalid hints.
   if (Hint && (!TargetRegisterInfo::isPhysicalRegister(Hint) ||
-               !RC->contains(Hint) || !Allocatable.test(Hint)))
+               !RC->contains(Hint) || !RegClassInfo.isAllocatable(Hint)))
     Hint = 0;
 
   // Take hint when possible.
@@ -768,7 +765,7 @@ void RAFast::AllocateBasicBlock() {
   // Add live-in registers as live.
   for (MachineBasicBlock::livein_iterator I = MBB->livein_begin(),
          E = MBB->livein_end(); I != E; ++I)
-    if (Allocatable.test(*I))
+    if (RegClassInfo.isAllocatable(*I))
       definePhysReg(MII, *I, regReserved);
 
   SmallVector<unsigned, 8> VirtDead;
@@ -899,7 +896,7 @@ void RAFast::AllocateBasicBlock() {
         }
         continue;
       }
-      if (!Allocatable.test(Reg)) continue;
+      if (!RegClassInfo.isAllocatable(Reg)) continue;
       if (MO.isUse()) {
         usePhysReg(MO);
       } else if (MO.isEarlyClobber()) {
@@ -988,7 +985,7 @@ void RAFast::AllocateBasicBlock() {
       unsigned Reg = MO.getReg();
 
       if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
-        if (!Allocatable.test(Reg)) continue;
+        if (!RegClassInfo.isAllocatable(Reg)) continue;
         definePhysReg(MI, Reg, (MO.isImplicit() || MO.isDead()) ?
                                regFree : regReserved);
         continue;
@@ -1045,9 +1042,7 @@ bool RAFast::runOnMachineFunction(MachineFunction &Fn) {
   TRI = TM->getRegisterInfo();
   TII = TM->getInstrInfo();
   RegClassInfo.runOnMachineFunction(Fn);
-
   UsedInInstr.resize(TRI->getNumRegs());
-  Allocatable = TRI->getAllocatableSet(*MF);
 
   // initialize the virtual->physical register map to have a 'null'
   // mapping for all virtual registers