Subzero: Consider all instruction variables for register preference.

src/IceInstVarIter.h

 //===- subzero/src/IceInstVarIter.h - Iterate over inst vars ----*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 127 matching lines @@
 ///
 ///  6) Step2 increments the inner loop's control variable, as well as the
 ///  current variable index.
 ///
 /// We use Var -- which should be a valid C++ identifier -- to uniquify names
 /// -- e.g., i##Var instead of simply i because we want users to be able to use
 /// the iterator for cross-products involving instructions' variables.
 #define FOREACH_VAR_IN_INST(Var, Instr)                                        \
   for (SizeT Sz_I##Var##_ = 0, Sz_##Var##Index_ = 0,                           \
              Sz_SrcSize##Var##_ = (Instr).getSrcSize(), Sz_J##Var##_ = 0,      \
-             Sz_NumVars##Var##_ = 0;                                           \
-       Sz_I##Var##_ < Sz_SrcSize##Var##_; ++Sz_I##Var##_)                      \
+             Sz_NumVars##Var##_ = 0, Sz_Foreach_Break = 0;                     \
+       !Sz_Foreach_Break && Sz_I##Var##_ < Sz_SrcSize##Var##_; ++Sz_I##Var##_) \
     if (Operand *Sz_Op##Var##_ = nullptr)                                      \
       /*nothing*/;                                                             \
     else                                                                       \
       for (Variable *Var =                                                     \
                (Sz_J##Var##_ = 0,                                              \
                Sz_Op##Var##_ = (Instr).getSrc(Sz_I##Var##_),                   \
                Sz_NumVars##Var##_ = Sz_Op##Var##_->getNumVars(), nullptr);     \
-           Sz_J##Var##_ < Sz_NumVars##Var##_ &&                                \
+           !Sz_Foreach_Break && Sz_J##Var##_ < Sz_NumVars##Var##_ &&           \
            ((Var = Sz_Op##Var##_->getVar(Sz_J##Var##_)), true);                \
            ++Sz_J##Var##_, ++Sz_##Var##Index_)
 
 #define IsOnlyValidInFOREACH_VAR_IN_INST(V)                                    \
   (static_cast<const SizeT>(Sz_##V##_))
 #define IndexOfVarInInst(Var) IsOnlyValidInFOREACH_VAR_IN_INST(Var##Index)
 #define IndexOfVarOperandInInst(Var) IsOnlyValidInFOREACH_VAR_IN_INST(I##Var)
+#define FOREACH_VAR_IN_INST_BREAK                                              \
+  if (true) {                                                                  \
+    Sz_Foreach_Break = 1;                                                      \
+    continue;                                                                  \
+  } else {                                                                     \
+  }
 #undef OnlyValidIn_FOREACH_VAR_IN_INSTS
 
 #endif // SUBZERO_SRC_ICEINSTVARITER_H