Weight variables by their number of uses for register allocation.

src/IceTargetLoweringX8664.cpp

Index: src/IceTargetLoweringX8664.cpp
diff --git a/src/IceTargetLoweringX8664.cpp b/src/IceTargetLoweringX8664.cpp
index 76fffa04039c1de54e4884ab05aa55c9fdcf5c3f..4bb177ea5611e4aff8b96a2be40060f1f857ce87 100644
--- a/src/IceTargetLoweringX8664.cpp
+++ b/src/IceTargetLoweringX8664.cpp
@@ -449,7 +449,7 @@ void TargetX8664::addProlog(CfgNode *Node) {
       [&VariablesLinkedToSpillSlots](Variable *Var) {
         if (auto *SpillVar =
                 llvm::dyn_cast<typename Traits::SpillVariable>(Var)) {
-          assert(Var->getWeight().isZero());
+          assert(Var->mustNotHaveReg());
           if (SpillVar->getLinkedTo() && !SpillVar->getLinkedTo()->hasReg()) {
             VariablesLinkedToSpillSlots.push_back(Var);
             return true;