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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132514 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 23 insertions, 9 deletions

diff --git a/lib/CodeGen/RegAllocFast.cpp b/lib/CodeGen/RegAllocFast.cpp
index 58739ff31d..97652036f9 100644
--- a/lib/CodeGen/RegAllocFast.cpp
+++ b/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
diff --git a/lib/CodeGen/RegisterClassInfo.h b/lib/CodeGen/RegisterClassInfo.h
index e41ae9e8da..6f7d9c9496 100644
--- a/lib/CodeGen/RegisterClassInfo.h
+++ b/lib/CodeGen/RegisterClassInfo.h
@@ -95,6 +95,25 @@ public:
       return CalleeSaved[N-1];
     return 0;
   }
+
+  /// isReserved - Returns true when PhysReg is a reserved register.
+  ///
+  /// Reserved registers may belong to an allocatable register class, but the
+  /// target has explicitly requested that they are not used.
+  ///
+  bool isReserved(unsigned PhysReg) const {
+    return Reserved.test(PhysReg);
+  }
+
+  /// isAllocatable - Returns true when PhysReg belongs to an allocatable
+  /// register class and it hasn't been reserved.
+  ///
+  /// Allocatable registers may show up in the allocation order of some virtual
+  /// register, so a register allocator needs to track its liveness and
+  /// availability.
+  bool isAllocatable(unsigned PhysReg) const {
+    return TRI->get(PhysReg).inAllocatableClass && !isReserved(PhysReg);
+  }
 };
 } // end namespace llvm