Weight variables by their number of uses for register allocation.

src/IceInst.cpp

Index: src/IceInst.cpp
diff --git a/src/IceInst.cpp b/src/IceInst.cpp
index 4b89eb77b0fa88f5f692f637a5ef892305b1a62b..252cd51fd6bfb746eea2a0959ff6f5d6023d1848 100644
--- a/src/IceInst.cpp
+++ b/src/IceInst.cpp
@@ -179,6 +179,8 @@ bool Inst::liveness(InstNumberT InstNumber, LivenessBV &Live,
 
   Dead = false;
   if (Dest) {
+    // TODO(ascull): get the loop nest depth
+    Dest->addUse(1);
     SizeT VarNum = Liveness->getLiveIndex(Dest->getIndex());
     if (Live[VarNum]) {
       if (!isDestNonKillable()) {
@@ -203,7 +205,9 @@ bool Inst::liveness(InstNumberT InstNumber, LivenessBV &Live,
     Operand *Src = getSrc(I);
     SizeT NumVars = Src->getNumVars();
     for (SizeT J = 0; J < NumVars; ++J, ++VarIndex) {
-      const Variable *Var = Src->getVar(J);
+      Variable *Var = Src->getVar(J);
+      // TODO(ascull): get the loop nest depth
+      Var->addUse(1);
       SizeT VarNum = Liveness->getLiveIndex(Var->getIndex());
       if (!Live[VarNum]) {
         setLastUse(VarIndex);