basic_block: Add proxy member functions for the instruction list

Currently basic block kind of acts like a 'dumb struct' which makes things
a little more verbose to write (as opposed to keeping it all in one place,
I guess). It's also a little wonky conceptually, considering a block is
composed of instructions (i.e. 'contains' them).

So providing accessors that make it act more like a container can make working
with algorithms a little nicer. It also makes the API a little more
defined.

Ideally, the list would be only available through a function, but
currently, the pool allocator is exposed, which seems somewhat odd,
considering the block itself should manage its overall allocations
(with placement new, and regular new), rather than putting that
sanitizing directly on the IR emitter (it should just care about emission,
not block state). However, recontaining that can be followed up with,
as it's very trivial to do.

src/backend_x64/emit_x64.cpp

@@ -71,7 +71,7 @@ EmitX64::BlockDescriptor EmitX64::Emit(const Arm::LocationDescriptor descriptor,
 
     EmitCondPrelude(block);
 
-    for (auto iter = block.instructions.begin(); iter != block.instructions.end(); ++iter) {
+    for (auto iter = block.begin(); iter != block.end(); ++iter) {
         IR::Inst* inst = &*iter;
 
         // Call the relevant Emit* member function.

src/frontend/ir/basic_block.cpp

@@ -57,7 +57,7 @@ std::string DumpBlock(const IR::Block& block) {
         }
     };
 
-    for (auto inst = block.instructions.begin(); inst != block.instructions.end(); ++inst) {
+    for (auto inst = block.begin(); inst != block.end(); ++inst) {
         const Opcode op = inst->GetOpcode();
 
         if (GetTypeOf(op) != Type::Void) {

src/frontend/ir/basic_block.h

@@ -29,8 +29,38 @@ namespace IR {
  */
 class Block final {
 public:
+    using InstructionList        = Common::IntrusiveList<Inst>;
+    using iterator               = InstructionList::iterator;
+    using const_iterator         = InstructionList::const_iterator;
+    using reverse_iterator       = InstructionList::reverse_iterator;
+    using const_reverse_iterator = InstructionList::const_reverse_iterator;
+
     explicit Block(const Arm::LocationDescriptor& location) : location(location) {}
 
+    bool                   empty()   const { return instructions.empty();   }
+
+    Inst&                  front()         { return instructions.front();   }
+    const Inst&            front()   const { return instructions.front();   }
+
+    Inst&                  back()          { return instructions.back();    }
+    const Inst&            back()    const { return instructions.back();    }
+
+    iterator               begin()         { return instructions.begin();   }
+    const_iterator         begin()   const { return instructions.begin();   }
+    iterator               end()           { return instructions.end();     }
+    const_iterator         end()     const { return instructions.end();     }
+
+    reverse_iterator       rbegin()        { return instructions.rbegin();  }
+    const_reverse_iterator rbegin()  const { return instructions.rbegin();  }
+    reverse_iterator       rend()          { return instructions.rend();    }
+    const_reverse_iterator rend()    const { return instructions.rend();    }
+
+    const_iterator         cbegin()  const { return instructions.cbegin();  }
+    const_iterator         cend()    const { return instructions.cend();    }
+
+    const_reverse_iterator crbegin() const { return instructions.crbegin(); }
+    const_reverse_iterator crend()   const { return instructions.crend();   }
+
     /// Description of the starting location of this block
     Arm::LocationDescriptor location;
     /// Conditional to pass in order to execute this block
@@ -39,7 +69,7 @@ public:
     boost::optional<Arm::LocationDescriptor> cond_failed = {};
 
     /// List of instructions in this block.
-    Common::IntrusiveList<Inst> instructions;
+    InstructionList instructions;
     /// Memory pool for instruction list
     std::unique_ptr<Common::Pool> instruction_alloc_pool = std::make_unique<Common::Pool>(sizeof(Inst), 4096);
     /// Terminal instruction of this block.

src/frontend/translate/translate_arm.cpp

@@ -66,7 +66,7 @@ bool ArmTranslatorVisitor::ConditionPassed(Cond cond) {
 
     // non-AL cond
 
-    if (!ir.block.instructions.empty()) {
+    if (!ir.block.empty()) {
         // We've already emitted instructions. Quit for now, we'll make a new block here later.
         cond_state = ConditionalState::Break;
         ir.SetTerm(IR::Term::LinkBlockFast{ir.current_location});

src/ir_opt/dead_code_elimination_pass.cpp

@@ -61,18 +61,18 @@ void DeadCodeElimination(IR::Block& block) {
     // We iterate over the instructions in reverse order.
     // This is because removing an instruction reduces the number of uses for earlier instructions.
 
-    if (block.instructions.empty()) {
+    if (block.empty()) {
         return;
     }
 
-    auto iter = block.instructions.end();
+    auto iter = block.end();
     do {
         --iter;
         if (!iter->HasUses() && is_side_effect_free(iter->GetOpcode())) {
             iter->Invalidate();
             iter = block.instructions.erase(iter);
         }
-    } while (iter != block.instructions.begin());
+    } while (iter != block.begin());
 }
 
 } // namespace Optimization

src/ir_opt/get_set_elimination_pass.cpp

@@ -16,7 +16,7 @@ namespace Dynarmic {
 namespace Optimization {
 
 void GetSetElimination(IR::Block& block) {
-    using Iterator = decltype(block.instructions.begin());
+    using Iterator = decltype(block.begin());
     struct RegisterInfo {
         IR::Value register_value;
         bool set_instruction_present = false;
@@ -47,7 +47,7 @@ void GetSetElimination(IR::Block& block) {
         get_inst->ReplaceUsesWith(info.register_value);
     };
 
-    for (auto inst = block.instructions.begin(); inst != block.instructions.end(); ++inst) {
+    for (auto inst = block.begin(); inst != block.end(); ++inst) {
         switch (inst->GetOpcode()) {
             case IR::Opcode::SetRegister: {
                 Arm::Reg reg = inst->GetArg(0).GetRegRef();

src/ir_opt/verification_pass.cpp

@@ -16,7 +16,7 @@ namespace Dynarmic {
 namespace Optimization {
 
 void VerificationPass(const IR::Block& block) {
-    for (const auto& inst : block.instructions) {
+    for (const auto& inst : block) {
         for (size_t i = 0; i < inst.NumArgs(); i++) {
             IR::Type t1 = inst.GetArg(i).GetType();
             IR::Type t2 = IR::GetArgTypeOf(inst.GetOpcode(), i);
@@ -28,7 +28,7 @@ void VerificationPass(const IR::Block& block) {
     }
 
     std::map<IR::Inst*, size_t> actual_uses;
-    for (const auto& inst : block.instructions) {
+    for (const auto& inst : block) {
         for (size_t i = 0; i < inst.NumArgs(); i++) {
             if (!inst.GetArg(i).IsImmediate()) {
                 actual_uses[inst.GetArg(i).GetInst()]++;