Return address handling. Not happy with the design, but it (sorta) works.

src/alloy/hir/function_builder.cc

@@ -459,6 +459,12 @@ void FunctionBuilder::Return() {
   EndBlock();
 }
 
+void FunctionBuilder::SetReturnAddress(Value* value) {
+  Instr* i = AppendInstr(OPCODE_SET_RETURN_ADDRESS_info, 0);
+  i->set_src1(value);
+  i->src2.value = i->src3.value = NULL;
+}
+
 void FunctionBuilder::Branch(Label* label, uint32_t branch_flags) {
   Instr* i = AppendInstr(OPCODE_BRANCH_info, branch_flags);
   i->src1.label = label;

src/alloy/hir/function_builder.h

@@ -70,6 +70,7 @@ public:
   void CallIndirect(Value* value, uint32_t call_flags = 0);
   void CallIndirectTrue(Value* cond, Value* value, uint32_t call_flags = 0);
   void Return();
+  void SetReturnAddress(Value* value);
 
   void Branch(Label* label, uint32_t branch_flags = 0);
   void BranchIf(Value* cond, Label* true_label, Label* false_label,

src/alloy/hir/opcodes.h

@@ -75,6 +75,7 @@ enum Opcode {
   OPCODE_CALL_INDIRECT,
   OPCODE_CALL_INDIRECT_TRUE,
   OPCODE_RETURN,
+  OPCODE_SET_RETURN_ADDRESS,
 
   OPCODE_BRANCH,
   OPCODE_BRANCH_IF,

src/alloy/hir/opcodes.inl

@@ -74,6 +74,12 @@ DEFINE_OPCODE(
     OPCODE_SIG_X,
     OPCODE_FLAG_BRANCH);
 
+DEFINE_OPCODE(
+    OPCODE_SET_RETURN_ADDRESS,
+    "set_return_address",
+    OPCODE_SIG_X_V,
+    0);
+
 DEFINE_OPCODE(
     OPCODE_BRANCH,
     "branch",