Weight variables by their number of uses for register allocation.

src/IceInst.cpp

 //===- subzero/src/IceInst.cpp - High-level instruction implementation ----===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 185 matching lines @@
     return false;
   // Phi arguments only get added to Live in the predecessor node, but
   // we still need to update LiveRangesEnded.
   bool IsPhi = llvm::isa<InstPhi>(this);
   resetLastUses();
   SizeT VarIndex = 0;
   for (SizeT I = 0; I < getSrcSize(); ++I) {
     Operand *Src = getSrc(I);
     SizeT NumVars = Src->getNumVars();
     for (SizeT J = 0; J < NumVars; ++J, ++VarIndex) {
-      const Variable *Var = Src->getVar(J);

[jvoung (off chromium), 2015/08/28 20:31:45]

any reason for this change?

[ascull, 2015/08/28 21:22:36]

There was, but no longer. Done.

+      Variable *Var = Src->getVar(J);
       SizeT VarNum = Liveness->getLiveIndex(Var->getIndex());
       if (!Live[VarNum]) {
         setLastUse(VarIndex);
         if (!IsPhi) {
           Live[VarNum] = true;
           // For a variable in SSA form, its live range can end at
           // most once in a basic block.  However, after lowering to
           // two-address instructions, we end up with sequences like
           // "t=b;t+=c;a=t" where t's live range begins and ends
           // twice.  ICE only allows a variable to have a single
@@ skipping 757 matching lines @@
     // preserve these.
     return true;
   }
   if (!Dest->hasReg() && !SrcVar->hasReg() &&
       Dest->getStackOffset() == SrcVar->getStackOffset())
     return true;
   return false;
 }
 
 } // end of namespace Ice