Add support for undef values in ICE IR.

src/IceOperand.h

Index: src/IceOperand.h
diff --git a/src/IceOperand.h b/src/IceOperand.h
index 54ac48b88a28b83b4c0bc05c473fa1c536445c3b..286c7714559b04fa43709bef380c6781cefff301 100644
--- a/src/IceOperand.h
+++ b/src/IceOperand.h
@@ -31,6 +31,7 @@ public:
     kConstFloat,
     kConstDouble,
     kConstRelocatable,
+    kConstUndef,
     kConst_Num,
     kVariable,
     // Target-specific operand classes use kTarget as the starting
@@ -206,6 +207,38 @@ private:
   bool SuppressMangling;
 };
 
+// ConstantUndef represents an unspecified bit pattern.

[jvoung (off chromium), 2014/06/17 21:48:53]

The comment says it will be an unspecified bit pattern, which is still true even
if we make it 0.

However, it might be good to clarify that backends should try to make code
generation deterministic and lower to 0.

[wala, 2014/06/18 01:17:46]

Agreed; I've updated the comment.

+class ConstantUndef : public Constant {
+public:
+  static ConstantUndef *create(GlobalContext *Ctx, Type Ty,
+                               uint32_t PoolEntryID) {
+    return new (Ctx->allocate<ConstantUndef>()) ConstantUndef(Ty, PoolEntryID);
+  }
+
+  using Constant::emit;
+  virtual void emit(GlobalContext *Ctx) const {
+    Ostream &Str = Ctx->getStrEmit();
+    Str << "undef";
+  }
+
+  using Constant::dump;
+  virtual void dump(GlobalContext *Ctx) const {
+    Ostream &Str = Ctx->getStrEmit();
+    Str << "undef";
+  }
+
+  static bool classof(const Operand *Operand) {
+    return Operand->getKind() == kConstUndef;
+  }
+
+private:
+  ConstantUndef(Type Ty, uint32_t PoolEntryID)
+      : Constant(kConstUndef, Ty, PoolEntryID) {}
+  ConstantUndef(const ConstantUndef &) LLVM_DELETED_FUNCTION;
+  ConstantUndef &operator=(const ConstantUndef &) LLVM_DELETED_FUNCTION;
+  virtual ~ConstantUndef() {}
+};
+
 // RegWeight is a wrapper for a uint32_t weight value, with a
 // special value that represents infinite weight, and an addWeight()
 // method that ensures that W+infinity=infinity.