Subzero: Consider all instruction variables for register preference.

src/IceTargetLowering.cpp

 //===- subzero/src/IceTargetLowering.cpp - Basic lowering implementation --===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 63 matching lines @@
 void LoweringContext::availabilityReset() {
   LastDest = nullptr;
   LastSrc = nullptr;
 }
 
 void LoweringContext::availabilityUpdate() {
   availabilityReset();
   Inst *Instr = LastInserted;
   if (Instr == nullptr)
     return;
-  if (!Instr->isSimpleAssign())
+  if (!Instr->isVarAssign())
     return;
-  if (auto *SrcVar = llvm::dyn_cast<Variable>(Instr->getSrc(0))) {
-    LastDest = Instr->getDest();
-    LastSrc = SrcVar;
-  }
+  // Since isVarAssign() is true, the source operand must be a Variable.
+  LastDest = Instr->getDest();
+  LastSrc = llvm::cast<Variable>(Instr->getSrc(0));
 }
 
 Variable *LoweringContext::availabilityGet(Operand *Src) const {
   assert(Src);
   if (Src == LastDest)
     return LastSrc;
   return nullptr;
 }
 
 TargetLowering *TargetLowering::createLowering(TargetArch Target, Cfg *Func) {
@@ skipping 526 matching lines @@
   if (Target == Target_##X)                                                    \
     return TargetHeader##X::create(Ctx);
 #include "llvm/Config/SZTargets.def"
 
   llvm::report_fatal_error("Unsupported target header lowering");
 }
 
 TargetHeaderLowering::~TargetHeaderLowering() = default;
 
 } // end of namespace Ice