From a9ba5bce0f7d0a55ccd2d49ff174052ccbfc913f Mon Sep 17 00:00:00 2001
From: wheremyfoodat <44909372+wheremyfoodat@users.noreply.github.com>
Date: Thu, 21 Aug 2025 02:18:07 +0300
Subject: [PATCH] Disassembly: Merge li a0 + syscall

---
 src/core/disr3000a.cc       | 47 +++++++++++++++++++++++++++++++++----
 src/core/disr3000a.h        |  5 ++++
 src/gui/widgets/assembly.cc |  5 ++++
 src/gui/widgets/assembly.h  |  1 +
 4 files changed, 53 insertions(+), 5 deletions(-)

diff --git a/src/core/disr3000a.cc b/src/core/disr3000a.cc
index 4cfd2edce..facaf4e78 100644
--- a/src/core/disr3000a.cc
+++ b/src/core/disr3000a.cc
@@ -57,6 +57,19 @@ const char *PCSX::Disasm::s_disRNameCP0[] = {
     "TagLo",    "TagHi",  "ErrorEPC", "*RES*",     // 1c
 };
 
+const char *PCSX::Disasm::getSyscallName(uint32_t index) {
+    switch (index) {
+        case 0:
+            return "NOP";
+        case 1:
+            return "EnterCriticalSection";
+        case 2:
+            return "ExitCriticalSection";
+        default:
+            return "DeliverEvent";
+    }
+}
+
 #undef declare
 #undef _Funct_
 #undef _Rd_
@@ -226,6 +239,7 @@ struct StringDisasm : public PCSX::Disasm {
             }
         }
     }
+    virtual void SyscallName(const char *name) final { append(name); }
     virtual void reset() final {
         m_buf[0] = 0;
         m_len = 0;
@@ -281,8 +295,9 @@ declare(disADDI) {
 declare(disADDIU) {
     if (_Rs_ == 0) {
         // this is the common pseudo-instruction to load an immediate 16 bits value
-        dOpCode("li");
-        GPR(_Rt_);
+        if (disLI(_Rt_, _Im_, nextCode, skipNext, delaySlotNext)) {
+            return;
+        }
     } else {
         dOpCode("addiu");
         GPR(_Rt_);
@@ -299,8 +314,9 @@ declare(disANDI) {
 declare(disORI) {
     if (_Rs_ == 0) {
         // while rare, this can also be used to load an immediate 16-bits value
-        dOpCode("li");
-        GPR(_Rt_);
+        if (disLI(_Rt_, _Im_, nextCode, skipNext, delaySlotNext)) {
+            return;
+        }
     } else {
         dOpCode("ori");
         GPR(_Rt_);
@@ -680,6 +696,27 @@ declare(disLUI) {
     }
 }
 
+bool PCSX::Disasm::disLI(uint32_t reg, uint32_t imm, uint32_t nextCode, bool *skipNext, bool *delaySlotNext) {
+    // Merge syscalls, which usually have the pattern
+    // li $a0, syscallNumber
+    // syscall 0x0000
+    uint8_t nextIns = nextCode >> 26;
+    uint8_t nextSubfunc = nextCode & 0x3f;
+
+    if (skipNext && reg == 4 && nextIns == 0 && nextSubfunc == 0xC) {
+        dOpCode("syscall");
+        SyscallName(getSyscallName(imm));
+
+        *skipNext = true;
+        return true;
+    } else {
+        dOpCode("li");
+        GPR(reg);
+
+        return false;
+    }
+}
+
 /*********************************************************
  * Move from HI/LO to GPR                                 *
  * Format:  OP rd                                         *
@@ -969,7 +1006,7 @@ declare(disCTC0) {
 }
 
 /*********************************************************
- * Unknow instruction (would generate an exception)       *
+ * Unknown instruction (would generate an exception)      *
  * Format:  ?                                             *
  *********************************************************/
 declare(disNULL) {
diff --git a/src/core/disr3000a.h b/src/core/disr3000a.h
index 07d0b4825..6dfda853e 100644
--- a/src/core/disr3000a.h
+++ b/src/core/disr3000a.h
@@ -36,6 +36,7 @@ class Disasm {
     static const char *s_disRNameCP2D[];
     static const char *s_disRNameCP2C[];
     static const char *s_disRNameCP0[];
+    static const char *getSyscallName(uint32_t index);
 
 #define declare(n) \
     void n(uint32_t code, uint32_t nextCode, uint32_t pc, bool *skipNext = nullptr, bool *delaySlotNext = nullptr)
@@ -72,6 +73,7 @@ class Disasm {
     virtual void OfB(int16_t offset, uint8_t reg, int size) = 0;
     virtual void BranchDest(uint32_t offset) = 0;
     virtual void Offset(uint32_t offset, int size) = 0;
+    virtual void SyscallName(const char *) = 0;
 
   private:
     // Type definition of our functions
@@ -188,6 +190,9 @@ class Disasm {
     declare(disGPL);
     declare(disNCCT);
 #undef declare
+
+    // li has a slightly different signature, being a pseudoinstruction
+    bool disLI(uint32_t reg, uint32_t imm, uint32_t nextCode, bool *skipNext = nullptr, bool *delaySlotNext = nullptr);
 };
 
 }  // namespace PCSX
diff --git a/src/gui/widgets/assembly.cc b/src/gui/widgets/assembly.cc
index 1eb539693..5823b1d84 100644
--- a/src/gui/widgets/assembly.cc
+++ b/src/gui/widgets/assembly.cc
@@ -104,6 +104,7 @@ class DummyAsm : public PCSX::Disasm {
     virtual void OfB(int16_t offset, uint8_t reg, int size) final {}
     virtual void BranchDest(uint32_t offset) final {}
     virtual void Offset(uint32_t offset, int size) final {}
+    virtual void SyscallName(const char*) final {}
 };
 
 }  // namespace
@@ -310,6 +311,10 @@ void PCSX::Widgets::Assembly::Target(uint32_t value) {
     }
     ImGui::PopStyleVar();
 }
+void PCSX::Widgets::Assembly::SyscallName(const char* name) {
+    sameLine();
+    ImGui::TextUnformatted(name);
+}
 void PCSX::Widgets::Assembly::Sa(uint8_t value) {
     comma();
     sameLine();
diff --git a/src/gui/widgets/assembly.h b/src/gui/widgets/assembly.h
index f3ef27843..b817f2148 100644
--- a/src/gui/widgets/assembly.h
+++ b/src/gui/widgets/assembly.h
@@ -92,6 +92,7 @@ class Assembly : private Disasm {
     virtual void OfB(int16_t offset, uint8_t reg, int size) final;
     virtual void BranchDest(uint32_t value) final;
     virtual void Offset(uint32_t addr, int size) final;
+    virtual void SyscallName(const char*) final;
     bool m_gotArg = false;
     bool m_notch = false;
     bool m_notchAfterSkip[2] = {false, false};