ir_emitter: Allow the insertion point for new instructions to be set

src/frontend/ir/basic_block.cpp

@@ -21,6 +21,10 @@
 namespace Dynarmic::IR {
 
 void Block::AppendNewInst(Opcode opcode, std::initializer_list<IR::Value> args) {
+    PrependNewInst(end(), opcode, args);
+}
+
+Block::iterator Block::PrependNewInst(iterator insertion_point, Opcode opcode, std::initializer_list<Value> args) {
     IR::Inst* inst = new(instruction_alloc_pool->Alloc()) IR::Inst(opcode);
     ASSERT(args.size() == inst->NumArgs());
 
@@ -29,7 +33,7 @@ void Block::AppendNewInst(Opcode opcode, std::initializer_list<IR::Value> args)
         index++;
     });
 
-    instructions.push_back(inst);
+    return instructions.insert_before(insertion_point, inst);
 }
 
 LocationDescriptor Block::Location() const {

src/frontend/ir/basic_block.h

@@ -69,7 +69,7 @@ public:
     const_reverse_iterator crend()   const { return instructions.crend();   }
 
     /**
-     * Appends a new instruction to this basic block,
+     * Appends a new instruction to the end of this basic block,
      * handling any allocations necessary to do so.
      *
      * @param op   Opcode representing the instruction to add.
@@ -77,6 +77,17 @@ public:
      */
     void AppendNewInst(Opcode op, std::initializer_list<Value> args);
 
+    /**
+     * Prepends a new instruction to this basic block before the insertion point,
+     * handling any allocations necessary to do so.
+     *
+     * @param insertion_point Where to insert the new instruction.
+     * @param op              Opcode representing the instruction to add.
+     * @param args            A sequence of Value instances used as arguments for the instruction.
+     * @returns Iterator to the newly created instruction.
+     */
+    iterator PrependNewInst(iterator insertion_point, Opcode op, std::initializer_list<Value> args);
+
     /// Gets the starting location for this basic block.
     LocationDescriptor Location() const;
     /// Gets the end location for this basic block.

src/frontend/ir/ir_emitter.cpp

@@ -944,4 +944,12 @@ void IREmitter::SetTerm(const Terminal& terminal) {
     block.SetTerminal(terminal);
 }
 
+void IREmitter::SetInsertionPoint(IR::Inst* new_insertion_point) {
+    insertion_point = IR::Block::iterator{*new_insertion_point};
+}
+
+void IREmitter::SetInsertionPoint(IR::Block::iterator new_insertion_point) {
+    insertion_point = new_insertion_point;
+}
+
 } // namespace Dynarmic::IR

src/frontend/ir/ir_emitter.h

@@ -55,7 +55,7 @@ struct ResultAndGE {
  */
 class IREmitter {
 public:
-    explicit IREmitter(Block& block) : block(block) {}
+    explicit IREmitter(Block& block) : block(block), insertion_point(block.end()) {}
 
     Block& block;
 
@@ -247,11 +247,16 @@ public:
 
     void SetTerm(const Terminal& terminal);
 
+    void SetInsertionPoint(IR::Inst* new_insertion_point);
+    void SetInsertionPoint(IR::Block::iterator new_insertion_point);
+
 protected:
+    IR::Block::iterator insertion_point;
+
     template<typename T = Value, typename ...Args>
     T Inst(Opcode op, Args ...args) {
-        block.AppendNewInst(op, {Value(args)...});
+        auto iter = block.PrependNewInst(insertion_point, op, {Value(args)...});
-        return T(Value(&block.back()));
+        return T(Value(&*iter));
     }
 };