Initial Subzero WASM prototype.

src/IceOperand.h

Index: src/IceOperand.h
diff --git a/src/IceOperand.h b/src/IceOperand.h
index bc48b74da0639623550479d341a400dc5ec01dde..2c1fc5dca9030397d056f3d7023f98aa0000e8f3 100644
--- a/src/IceOperand.h
+++ b/src/IceOperand.h
@@ -94,6 +94,10 @@ public:
 
   virtual ~Operand() = default;
 
+  CfgNode *getDefNode() const { return DefNode; }
+
+  void setDefNode(CfgNode *node) { this->DefNode = node; }
+
 protected:
   Operand(OperandKind Kind, Type Ty) : Ty(Ty), Kind(Kind) {
     // It is undefined behavior to have a larger value in the enum
@@ -105,6 +109,8 @@ protected:
   /// Vars and NumVars are initialized by the derived class.
   SizeT NumVars = 0;
   Variable **Vars = nullptr;
+
+  CfgNode *DefNode = nullptr;
 };
 
 template <class StreamType>
@@ -739,6 +745,9 @@ public:
     return Kind >= kVariable && Kind <= kVariable_Max;
   }
 
+  void setDefiningInst(Inst *I) { DefiningInst = I; }
+  Inst *getDefiningInst() const { return DefiningInst; }
+
 protected:
   Variable(OperandKind K, Type Ty, SizeT Index)
       : Operand(K, Ty), Number(Index),
@@ -772,6 +781,8 @@ protected:
   LiveRange Live;
   /// VarsReal (and Operand::Vars) are set up such that Vars[0] == this.
   Variable *VarsReal[1];
+  /// A pointer to the instruction of which this is the destination.
+  Inst *DefiningInst = nullptr;

[Jim Stichnoth, 2016/03/29 17:49:57]

I'm not super excited about increasing the size of
operands/variable/instructions for what is currently wasm-specific info.

Also, I don't see that this info is being updated when:
1) the defining instruction changes e.g. during lowering when the original
defining instruction is deleted and a new one is inserted
2) the defining node changes due to node splitting

I think a more appropriate approach would be to maintain various unordered_maps
during parsing and then discard them after all is parsed.

[Eric Holk, 2016/03/29 22:58:07]

I added a couple unordered_maps and removed the extra fields. They allocate from
the CFG right now, which may not be ideal, but it at least keeps the memory
usage the same on non-WASM paths.

 };
 
 // Variable64On32 represents a 64-bit variable on a 32-bit architecture. In