Keep track of which registers are related to which other registers.

Use this information to avoid doing expensive interval intersections for
registers that could not possible be interesting.  This speeds up linscan
on ia64 compiling kc++ in release mode from taking 7.82s to 4.8s(!), total
itanium llc time on this program is 27.3s now.  This marginally speeds up
PPC and X86, but they appear to be limited by other parts of linscan, not
this code.

On this program, on itanium, live intervals now takes 41% of llc time.

llvm-svn: 22986

lib/CodeGen/RegAllocLinearScan.cpp

@@ -12,6 +12,9 @@
 //===----------------------------------------------------------------------===//
 
 #define DEBUG_TYPE "regalloc"
+#include "LiveIntervalAnalysis.h"
+#include "PhysRegTracker.h"
+#include "VirtRegMap.h"
 #include "llvm/Function.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineInstr.h"
@@ -19,12 +22,10 @@
 #include "llvm/CodeGen/SSARegMap.h"
 #include "llvm/Target/MRegisterInfo.h"
 #include "llvm/Target/TargetMachine.h"
-#include "llvm/Support/Debug.h"
+#include "llvm/ADT/EquivalenceClasses.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/STLExtras.h"
-#include "LiveIntervalAnalysis.h"
-#include "PhysRegTracker.h"
-#include "VirtRegMap.h"
+#include "llvm/Support/Debug.h"
 #include <algorithm>
 #include <cmath>
 #include <set>
@@ -44,6 +45,12 @@ namespace {
     typedef std::pair<LiveInterval*, LiveInterval::iterator> IntervalPtr;
     typedef std::vector<IntervalPtr> IntervalPtrs;
   private:
+    /// RelatedRegClasses - This structure is built the first time a function is
+    /// compiled, and keeps track of which register classes have registers that
+    /// belong to multiple classes or have aliases that are in other classes.
+    EquivalenceClasses<const TargetRegisterClass*> RelatedRegClasses;
+    std::map<unsigned, const TargetRegisterClass*> OneClassForEachPhysReg;
+
     MachineFunction* mf_;
     const TargetMachine* tm_;
     const MRegisterInfo* mri_;
@@ -119,6 +126,8 @@ namespace {
     /// stack slot. returns the stack slot
     int assignVirt2StackSlot(unsigned virtReg);
 
+    void ComputeRelatedRegClasses();
+
     template <typename ItTy>
     void printIntervals(const char* const str, ItTy i, ItTy e) const {
       if (str) std::cerr << str << " intervals:\n";
@@ -134,12 +143,51 @@ namespace {
   };
 }
 
+void RA::ComputeRelatedRegClasses() {
+  const MRegisterInfo &MRI = *mri_;
+  
+  // First pass, add all reg classes to the union, and determine at least one
+  // reg class that each register is in.
+  bool HasAliases = false;
+  for (MRegisterInfo::regclass_iterator RCI = MRI.regclass_begin(),
+       E = MRI.regclass_end(); RCI != E; ++RCI) {
+    RelatedRegClasses.insert(*RCI);
+    for (TargetRegisterClass::iterator I = (*RCI)->begin(), E = (*RCI)->end();
+         I != E; ++I) {
+      HasAliases = HasAliases || *MRI.getAliasSet(*I) != 0;
+      
+      const TargetRegisterClass *&PRC = OneClassForEachPhysReg[*I];
+      if (PRC) {
+        // Already processed this register.  Just make sure we know that
+        // multiple register classes share a register.
+        RelatedRegClasses.unionSets(PRC, *RCI);
+      } else {
+        PRC = *RCI;
+      }
+    }
+  }
+  
+  // Second pass, now that we know conservatively what register classes each reg
+  // belongs to, add info about aliases.  We don't need to do this for targets
+  // without register aliases.
+  if (HasAliases)
+    for (std::map<unsigned, const TargetRegisterClass*>::iterator
+         I = OneClassForEachPhysReg.begin(), E = OneClassForEachPhysReg.end();
+         I != E; ++I)
+      for (const unsigned *AS = MRI.getAliasSet(I->first); *AS; ++AS)
+        RelatedRegClasses.unionSets(I->second, OneClassForEachPhysReg[*AS]);
+}
+
 bool RA::runOnMachineFunction(MachineFunction &fn) {
   mf_ = &fn;
   tm_ = &fn.getTarget();
   mri_ = tm_->getRegisterInfo();
   li_ = &getAnalysis<LiveIntervals>();
 
+  // If this is the first function compiled, compute the related reg classes.
+  if (RelatedRegClasses.empty())
+    ComputeRelatedRegClasses();
+  
   PhysRegsUsed = new bool[mri_->getNumRegs()];
   std::fill(PhysRegsUsed, PhysRegsUsed+mri_->getNumRegs(), false);
   fn.setUsedPhysRegs(PhysRegsUsed);
@@ -367,18 +415,24 @@ void RA::assignRegOrStackSlotAtInterval(LiveInterval* cur)
 
   std::vector<std::pair<unsigned, float> > SpillWeightsToAdd;
   unsigned StartPosition = cur->beginNumber();
-
+  const TargetRegisterClass *RC = mf_->getSSARegMap()->getRegClass(cur->reg);
+  const TargetRegisterClass *RCLeader = RelatedRegClasses.getLeaderValue(RC);
+      
   // for every interval in inactive we overlap with, mark the
   // register as not free and update spill weights.
   for (IntervalPtrs::const_iterator i = inactive_.begin(),
          e = inactive_.end(); i != e; ++i) {
-    if (cur->overlapsFrom(*i->first, i->second-1)) {
-      unsigned reg = i->first->reg;
-      assert(MRegisterInfo::isVirtualRegister(reg) &&
-             "Can only allocate virtual registers!");
-      reg = vrm_->getPhys(reg);
-      prt_->addRegUse(reg);
-      SpillWeightsToAdd.push_back(std::make_pair(reg, i->first->weight));
+    unsigned Reg = i->first->reg;
+    assert(MRegisterInfo::isVirtualRegister(Reg) &&
+           "Can only allocate virtual registers!");
+    const TargetRegisterClass *RegRC = mf_->getSSARegMap()->getRegClass(Reg);
+    // If this is not in a related reg class to the register we're allocating, 
+    // don't check it.
+    if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader &&
+        cur->overlapsFrom(*i->first, i->second-1)) {
+      Reg = vrm_->getPhys(Reg);
+      prt_->addRegUse(Reg);
+      SpillWeightsToAdd.push_back(std::make_pair(Reg, i->first->weight));
     }
   }
   
@@ -415,12 +469,15 @@ void RA::assignRegOrStackSlotAtInterval(LiveInterval* cur)
     // out to be in use.  Actually add all of the conflicting fixed registers to
     // prt so we can do an accurate query.
     if (ConflictsWithFixed) {
-      // For every interval in fixed we overlap with, mark the register as not free
-      // and update spill weights.
+      // For every interval in fixed we overlap with, mark the register as not
+      // free and update spill weights.
       for (unsigned i = 0, e = fixed_.size(); i != e; ++i) {
         IntervalPtr &IP = fixed_[i];
         LiveInterval *I = IP.first;
-        if (I->endNumber() > StartPosition) {
+
+        const TargetRegisterClass *RegRC = OneClassForEachPhysReg[I->reg];
+        if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader &&       
+            I->endNumber() > StartPosition) {
           LiveInterval::iterator II = I->advanceTo(IP.second, StartPosition);
           IP.second = II;
           if (II != I->begin() && II->start > StartPosition)
@@ -476,9 +533,8 @@ void RA::assignRegOrStackSlotAtInterval(LiveInterval* cur)
 
   float minWeight = float(HUGE_VAL);
   unsigned minReg = 0;
-  const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
-  for (TargetRegisterClass::iterator i = rc->allocation_order_begin(*mf_),
-       e = rc->allocation_order_end(*mf_); i != e; ++i) {
+  for (TargetRegisterClass::iterator i = RC->allocation_order_begin(*mf_),
+       e = RC->allocation_order_end(*mf_); i != e; ++i) {
     unsigned reg = *i;
     if (minWeight > SpillWeights[reg]) {
       minWeight = SpillWeights[reg];
@@ -649,14 +705,23 @@ unsigned RA::getFreePhysReg(LiveInterval* cur)
   std::vector<unsigned> inactiveCounts(mri_->getNumRegs(), 0);
   unsigned MaxInactiveCount = 0;
   
+  const TargetRegisterClass *RC = mf_->getSSARegMap()->getRegClass(cur->reg);
+  const TargetRegisterClass *RCLeader = RelatedRegClasses.getLeaderValue(RC);
+ 
   for (IntervalPtrs::iterator i = inactive_.begin(), e = inactive_.end();
        i != e; ++i) {
     unsigned reg = i->first->reg;
     assert(MRegisterInfo::isVirtualRegister(reg) &&
            "Can only allocate virtual registers!");
-    reg = vrm_->getPhys(reg);
-    ++inactiveCounts[reg];
-    MaxInactiveCount = std::max(MaxInactiveCount, inactiveCounts[reg]);
+
+    // If this is not in a related reg class to the register we're allocating, 
+    // don't check it.
+    const TargetRegisterClass *RegRC = mf_->getSSARegMap()->getRegClass(reg);
+    if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader) {
+      reg = vrm_->getPhys(reg);
+      ++inactiveCounts[reg];
+      MaxInactiveCount = std::max(MaxInactiveCount, inactiveCounts[reg]);
+    }
   }
 
   const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);