Subzero: Optimize live range overlaps() computation through trimming.

src/IceRegAlloc.cpp

 //===- subzero/src/IceRegAlloc.cpp - Linear-scan implementation -----------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the LinearScan class, which performs the
 // linear-scan register allocation after liveness analysis has been
 // performed.
 //
 //===----------------------------------------------------------------------===//
 
 #include "IceCfg.h"
 #include "IceInst.h"
 #include "IceOperand.h"
 #include "IceRegAlloc.h"
 #include "IceTargetLowering.h"
 
 namespace Ice {
 
 namespace {
 
 // Returns true if Var has any definitions within Item's live range.
+// TODO(stichnot): Consider trimming the Definitions list similar to
+// how the live ranges are trimmed, since all the overlapsDefs() tests
+// are whether some variable's definitions overlap Cur, and trimming
+// is with respect Cur.start.  Initial tests show no measurable
+// performance difference, so we'll keep the code simple for now.
 bool overlapsDefs(const Cfg *Func, const LiveRangeWrapper &Item,
                   const Variable *Var) {
-  const InstDefList &Defs = Func->getVMetadata()->getDefinitions(Var);
+  const bool UseTrimmed = true;
+  VariablesMetadata *VMetadata = Func->getVMetadata();
+  const InstDefList &Defs = VMetadata->getDefinitions(Var);
   for (size_t i = 0; i < Defs.size(); ++i) {
-    if (Item.range().overlaps(Defs[i]->getNumber()))
+    if (Item.range().overlapsInst(Defs[i]->getNumber(), UseTrimmed))
       return true;
   }
   return false;
 }
 
 void dumpDisableOverlap(const Cfg *Func, const Variable *Var,
                         const char *Reason) {
   if (Func->getContext()->isVerbose(IceV_LinearScan)) {
+    VariablesMetadata *VMetadata = Func->getVMetadata();
     Ostream &Str = Func->getContext()->getStrDump();
     Str << "Disabling Overlap due to " << Reason << " " << *Var
         << " LIVE=" << Var->getLiveRange() << " Defs=";
-    const InstDefList &Defs = Func->getVMetadata()->getDefinitions(Var);
+    const InstDefList &Defs = VMetadata->getDefinitions(Var);
     for (size_t i = 0; i < Defs.size(); ++i) {
       if (i > 0)
         Str << ",";
       Str << Defs[i]->getNumber();
     }
     Str << "\n";
   }
 }
 
 } // end of anonymous namespace
@@ skipping 37 matching lines @@
     TimerMarker T(IDinitUnhandled, Func->getContext());
     for (Variable *Var : Vars) {
       // Explicitly don't consider zero-weight variables, which are
       // meant to be spill slots.
       if (Var->getWeight() == RegWeight::Zero)
         continue;
       // Don't bother if the variable has a null live range, which means
       // it was never referenced.
       if (Var->getLiveRange().isEmpty())
         continue;
+      Var->untrimLiveRange();
       LiveRangeWrapper R(Var);
       Unhandled.insert(R);
       if (Var->hasReg()) {
         Var->setRegNumTmp(Var->getRegNum());
         Var->setLiveRangeInfiniteWeight();
         UnhandledPrecolored.insert(R);
       }
     }
   }
 
@@ skipping 41 matching lines @@
       assert(UnhandledPrecolored.begin()->Var == Cur.Var);
       UnhandledPrecolored.erase(UnhandledPrecolored.begin());
       continue;
     }
 
     // Check for active ranges that have expired or become inactive.
     for (auto I = Active.begin(), E = Active.end(); I != E; I = Next) {
       Next = I;
       ++Next;
       LiveRangeWrapper Item = *I;
+      Item.Var->trimLiveRange(Cur.range().getStart());
       bool Moved = false;
       if (Item.endsBefore(Cur)) {
         // Move Item from Active to Handled list.
         if (Verbose) {
           Str << "Expiring     ";
           Item.dump(Func);
           Str << "\n";
         }
         Active.erase(I);
         Handled.push_back(Item);
@@ skipping 16 matching lines @@
         --RegUses[RegNum];
         assert(RegUses[RegNum] >= 0);
       }
     }
 
     // Check for inactive ranges that have expired or reactivated.
     for (auto I = Inactive.begin(), E = Inactive.end(); I != E; I = Next) {
       Next = I;
       ++Next;
       LiveRangeWrapper Item = *I;
+      Item.Var->trimLiveRange(Cur.range().getStart());
+      // As an optimization, don't bother checking pure point-valued
+      // Inactive ranges, because the overlapsStart() test will never
+      // succeed, and the endsBefore() test will generally only
+      // succeed after the last call instruction, which statistically
+      // happens near the end.  TODO(stichnot): Consider suppressing
+      // this check every N iterations in case calls are only at the
+      // beginning of the function.
+      if (!Item.range().isNonpoints())
+        continue;
       if (Item.endsBefore(Cur)) {
         // Move Item from Inactive to Handled list.
         if (Verbose) {
           Str << "Expiring     ";
           Item.dump(Func);
           Str << "\n";
         }
         Inactive.erase(I);
         Handled.push_back(Item);
       } else if (Item.overlapsStart(Cur)) {
@@ skipping 342 matching lines @@
     Str << "\n";
   }
   Str << "++++++ Inactive:\n";
   for (const LiveRangeWrapper &Item : Inactive) {
     Item.dump(Func);
     Str << "\n";
   }
 }
 
 } // end of namespace Ice