ir/terminal: Add FastDispatchHint

src/backend/x64/a32_emit_x64.cpp

@@ -1230,14 +1230,8 @@ void A32EmitX64::EmitTerminalImpl(IR::Term::PopRSBHint, IR::LocationDescriptor)
     code.or_(ebx, dword[r15 + offsetof(A32JitState, CPSR_et)]);
     code.or_(rbx, rcx);
 
-    code.mov(eax, dword[r15 + offsetof(A32JitState, rsb_ptr)]);
+void A32EmitX64::EmitTerminalImpl(IR::Term::FastDispatchHint, IR::LocationDescriptor initial_location) {
-    code.sub(eax, 1);
+    EmitTerminalImpl(IR::Term::ReturnToDispatch{}, initial_location);
-    code.and_(eax, u32(A32JitState::RSBPtrMask));
-    code.mov(dword[r15 + offsetof(A32JitState, rsb_ptr)], eax);
-    code.cmp(rbx, qword[r15 + offsetof(A32JitState, rsb_location_descriptors) + rax * sizeof(u64)]);
-    code.jne(code.GetReturnFromRunCodeAddress());
-    code.mov(rax, qword[r15 + offsetof(A32JitState, rsb_codeptrs) + rax * sizeof(u64)]);
-    code.jmp(rax);
 }
 
 void A32EmitX64::EmitTerminalImpl(IR::Term::If terminal, IR::LocationDescriptor initial_location) {

src/backend/x64/a32_emit_x64.h

@@ -77,6 +77,7 @@ protected:
     void EmitTerminalImpl(IR::Term::LinkBlock terminal, IR::LocationDescriptor initial_location) override;
     void EmitTerminalImpl(IR::Term::LinkBlockFast terminal, IR::LocationDescriptor initial_location) override;
     void EmitTerminalImpl(IR::Term::PopRSBHint terminal, IR::LocationDescriptor initial_location) override;
+    void EmitTerminalImpl(IR::Term::FastDispatchHint terminal, IR::LocationDescriptor initial_location) override;
     void EmitTerminalImpl(IR::Term::If terminal, IR::LocationDescriptor initial_location) override;
     void EmitTerminalImpl(IR::Term::CheckBit terminal, IR::LocationDescriptor initial_location) override;
     void EmitTerminalImpl(IR::Term::CheckHalt terminal, IR::LocationDescriptor initial_location) override;

src/backend/x64/a64_emit_x64.cpp

@@ -1070,6 +1070,10 @@ void A64EmitX64::EmitTerminalImpl(IR::Term::PopRSBHint, IR::LocationDescriptor)
     code.jmp(rax);
 }
 
+void A64EmitX64::EmitTerminalImpl(IR::Term::FastDispatchHint, IR::LocationDescriptor initial_location) {
+    EmitTerminalImpl(IR::Term::ReturnToDispatch{}, initial_location);
+}
+
 void A64EmitX64::EmitTerminalImpl(IR::Term::If terminal, IR::LocationDescriptor initial_location) {
     switch (terminal.if_) {
     case IR::Cond::AL:

src/backend/x64/a64_emit_x64.h

@@ -83,6 +83,7 @@ protected:
     void EmitTerminalImpl(IR::Term::LinkBlock terminal, IR::LocationDescriptor initial_location) override;
     void EmitTerminalImpl(IR::Term::LinkBlockFast terminal, IR::LocationDescriptor initial_location) override;
     void EmitTerminalImpl(IR::Term::PopRSBHint terminal, IR::LocationDescriptor initial_location) override;
+    void EmitTerminalImpl(IR::Term::FastDispatchHint terminal, IR::LocationDescriptor initial_location) override;
     void EmitTerminalImpl(IR::Term::If terminal, IR::LocationDescriptor initial_location) override;
     void EmitTerminalImpl(IR::Term::CheckBit terminal, IR::LocationDescriptor initial_location) override;
     void EmitTerminalImpl(IR::Term::CheckHalt terminal, IR::LocationDescriptor initial_location) override;

src/backend/x64/emit_x64.h

@@ -100,6 +100,7 @@ protected:
     virtual void EmitTerminalImpl(IR::Term::LinkBlock terminal, IR::LocationDescriptor initial_location) = 0;
     virtual void EmitTerminalImpl(IR::Term::LinkBlockFast terminal, IR::LocationDescriptor initial_location) = 0;
     virtual void EmitTerminalImpl(IR::Term::PopRSBHint terminal, IR::LocationDescriptor initial_location) = 0;
+    virtual void EmitTerminalImpl(IR::Term::FastDispatchHint terminal, IR::LocationDescriptor initial_location) = 0;
     virtual void EmitTerminalImpl(IR::Term::If terminal, IR::LocationDescriptor initial_location) = 0;
     virtual void EmitTerminalImpl(IR::Term::CheckBit terminal, IR::LocationDescriptor initial_location) = 0;
     virtual void EmitTerminalImpl(IR::Term::CheckHalt terminal, IR::LocationDescriptor initial_location) = 0;

src/frontend/ir/terminal.h

@@ -29,7 +29,7 @@ struct Interpret {
 
 /**
  * This terminal instruction returns control to the dispatcher.
- * The dispatcher will use the value in R15 to determine what comes next.
+ * The dispatcher will use the current cpu state to determine what comes next.
  */
 struct ReturnToDispatch {};
 
@@ -57,14 +57,21 @@ struct LinkBlockFast {
 };
 
 /**
- * This terminal instruction checks the top of the Return Stack Buffer against R15.
+ * This terminal instruction checks the top of the Return Stack Buffer against the current
- * If RSB lookup fails, control is returned to the dispatcher.
+ * location descriptor. If RSB lookup fails, control is returned to the dispatcher.
  * This is an optimization for faster function calls. A backend that doesn't support
  * this optimization or doesn't have a RSB may choose to implement this exactly as
  * ReturnToDispatch.
  */
 struct PopRSBHint {};
 
+/**
+ * This terminal instruction performs a lookup of the current location descriptor in the
+ * fast dispatch lookup table. A backend that doesn't support this optimization may choose
+ * to implement this exactly as ReturnToDispatch.
+ */
+struct FastDispatchHint {};
+
 struct If;
 struct CheckBit;
 struct CheckHalt;
@@ -76,6 +83,7 @@ using Terminal = boost::variant<
         LinkBlock,
         LinkBlockFast,
         PopRSBHint,
+        FastDispatchHint,
         boost::recursive_wrapper<If>,
         boost::recursive_wrapper<CheckBit>,
         boost::recursive_wrapper<CheckHalt>