Add support for undef values in ICE IR.

src/IceTargetLoweringX8632.cpp

 //===- subzero/src/IceTargetLoweringX8632.cpp - x86-32 lowering -----------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the TargetLoweringX8632 class, which
@@ skipping 2134 matching lines @@
     }
 
     if (!(Allowed & Legal_Mem)) {
       Variable *Reg = makeReg(From->getType(), RegNum);
       _mov(Reg, From, RegNum);
       From = Reg;
     }
     return From;
   }
   if (llvm::isa<Constant>(From)) {
+    if (llvm::isa<ConstantUndef>(From)) {
+      // Lower undefs to zero. Another option is to lower undefs to an

[Jim Stichnoth, 2014/06/18 13:43:33]

Please help future developers. :)  Leave the FakeDef instruction creation in the
code as a comment.

+      // uninitialized register; however, using an uninitialized register
+      // results in less predictable code.
+      From = Ctx->getConstantZero(From->getType());
+    }
     if (!(Allowed & Legal_Imm)) {
       Variable *Reg = makeReg(From->getType(), RegNum);
       _mov(Reg, From);
       From = Reg;
     }
     return From;
   }
   if (Variable *Var = llvm::dyn_cast<Variable>(From)) {
     // We need a new physical register for the operand if:
     //   Mem is not allowed and Var->getRegNum() is unknown, or
@@ skipping 96 matching lines @@
   // llvm-mc doesn't parse "dword ptr [.L$foo]".
   Str << "dword ptr [L$" << IceType_f32 << "$" << getPoolEntryID() << "]";
 }
 
 template <> void ConstantDouble::emit(GlobalContext *Ctx) const {
   Ostream &Str = Ctx->getStrEmit();
   Str << "qword ptr [L$" << IceType_f64 << "$" << getPoolEntryID() << "]";
 }
 
 } // end of namespace Ice