From eb80aae9c0428cabb2ce9d1d7de14e83d5d5b003 Mon Sep 17 00:00:00 2001
From: MerryMage <MerryMage@users.noreply.github.com>
Date: Sun, 3 Dec 2017 15:22:49 +0000
Subject: [PATCH] block_of_code: Move MXCSR switching out of dispatch loop

Also clarify MXCSR entry/exit terminology
---
 src/backend_x64/block_of_code.cpp | 33 ++++++++++++++++---------------
 src/backend_x64/block_of_code.h   |  6 +++---
 src/backend_x64/emit_x64.cpp      |  2 +-
 3 files changed, 21 insertions(+), 20 deletions(-)

diff --git a/src/backend_x64/block_of_code.cpp b/src/backend_x64/block_of_code.cpp
index 3bb8945e..2aa6210d 100644
--- a/src/backend_x64/block_of_code.cpp
+++ b/src/backend_x64/block_of_code.cpp
@@ -85,22 +85,22 @@ void BlockOfCode::RunCode(JitState* jit_state, size_t cycles_to_run) const {
     run_code(jit_state);
 }
 
-void BlockOfCode::ReturnFromRunCode(bool MXCSR_switch) {
+void BlockOfCode::ReturnFromRunCode(bool mxcsr_already_exited) {
     size_t index = 0;
-    if (!MXCSR_switch)
-        index |= NO_SWITCH_MXCSR;
+    if (mxcsr_already_exited)
+        index |= MXCSR_ALREADY_EXITED;
     jmp(return_from_run_code[index]);
 }
 
-void BlockOfCode::ForceReturnFromRunCode(bool MXCSR_switch) {
+void BlockOfCode::ForceReturnFromRunCode(bool mxcsr_already_exited) {
     size_t index = FORCE_RETURN;
-    if (!MXCSR_switch)
-        index |= NO_SWITCH_MXCSR;
+    if (mxcsr_already_exited)
+        index |= MXCSR_ALREADY_EXITED;
     jmp(return_from_run_code[index]);
 }
 
 void BlockOfCode::GenRunCode() {
-    Xbyak::Label loop;
+    Xbyak::Label loop, enter_mxcsr_then_loop;
 
     align();
     run_code = getCurr<RunCodeFuncType>();
@@ -119,22 +119,23 @@ void BlockOfCode::GenRunCode() {
 
     mov(r15, ABI_PARAM1);
 
+    L(enter_mxcsr_then_loop);
+    SwitchMxcsrOnEntry();
     L(loop);
     mov(ABI_PARAM1, u64(lookup_block_arg));
     CallFunction(lookup_block);
 
-    SwitchMxcsrOnEntry();
     jmp(ABI_RETURN);
 
     // Return from run code variants
-    const auto emit_return_from_run_code = [this, &loop](bool no_mxcsr_switch, bool force_return){
-        if (!no_mxcsr_switch) {
-            SwitchMxcsrOnExit();
-        }
-
+    const auto emit_return_from_run_code = [this, &loop, &enter_mxcsr_then_loop](bool mxcsr_already_exited, bool force_return){
         if (!force_return) {
             cmp(qword[r15 + offsetof(JitState, cycles_remaining)], 0);
-            jg(loop);
+            jg(mxcsr_already_exited ? enter_mxcsr_then_loop : loop);
+        }
+
+        if (!mxcsr_already_exited) {
+            SwitchMxcsrOnExit();
         }
 
         mov(ABI_PARAM1, qword[r15 + offsetof(JitState, cycles_to_run)]);
@@ -150,7 +151,7 @@ void BlockOfCode::GenRunCode() {
     emit_return_from_run_code(false, false);
 
     align();
-    return_from_run_code[NO_SWITCH_MXCSR] = getCurr<const void*>();
+    return_from_run_code[MXCSR_ALREADY_EXITED] = getCurr<const void*>();
     emit_return_from_run_code(true, false);
 
     align();
@@ -158,7 +159,7 @@ void BlockOfCode::GenRunCode() {
     emit_return_from_run_code(false, true);
 
     align();
-    return_from_run_code[NO_SWITCH_MXCSR | FORCE_RETURN] = getCurr<const void*>();
+    return_from_run_code[MXCSR_ALREADY_EXITED | FORCE_RETURN] = getCurr<const void*>();
     emit_return_from_run_code(true, true);
 }
 
diff --git a/src/backend_x64/block_of_code.h b/src/backend_x64/block_of_code.h
index a1cf4055..d2dd2182 100644
--- a/src/backend_x64/block_of_code.h
+++ b/src/backend_x64/block_of_code.h
@@ -34,9 +34,9 @@ public:
     /// Runs emulated code for approximately `cycles_to_run` cycles.
     void RunCode(JitState* jit_state, size_t cycles_to_run) const;
     /// Code emitter: Returns to dispatcher
-    void ReturnFromRunCode(bool MXCSR_switch = true);
+    void ReturnFromRunCode(bool mxcsr_already_exited = false);
     /// Code emitter: Returns to dispatcher, forces return to host
-    void ForceReturnFromRunCode(bool MXCSR_switch = true);
+    void ForceReturnFromRunCode(bool mxcsr_already_exited = false);
     /// Code emitter: Makes guest MXCSR the current MXCSR
     void SwitchMxcsrOnEntry();
     /// Code emitter: Makes saved host MXCSR the current MXCSR
@@ -145,7 +145,7 @@ private:
 
     using RunCodeFuncType = void(*)(JitState*);
     RunCodeFuncType run_code = nullptr;
-    static constexpr size_t NO_SWITCH_MXCSR = 1 << 0;
+    static constexpr size_t MXCSR_ALREADY_EXITED = 1 << 0;
     static constexpr size_t FORCE_RETURN = 1 << 1;
     std::array<const void*, 4> return_from_run_code;
     void GenRunCode();
diff --git a/src/backend_x64/emit_x64.cpp b/src/backend_x64/emit_x64.cpp
index f027417a..2c84ce7c 100644
--- a/src/backend_x64/emit_x64.cpp
+++ b/src/backend_x64/emit_x64.cpp
@@ -3371,7 +3371,7 @@ void EmitX64::EmitTerminal(IR::Term::Interpret terminal, IR::LocationDescriptor
     code->mov(MJitStateReg(Arm::Reg::PC), code->ABI_PARAM1.cvt32());
     code->SwitchMxcsrOnExit();
     code->CallFunction(cb.InterpreterFallback);
-    code->ReturnFromRunCode(false); // TODO: Check cycles
+    code->ReturnFromRunCode(true); // TODO: Check cycles
 }
 
 void EmitX64::EmitTerminal(IR::Term::ReturnToDispatch, IR::LocationDescriptor) {