From 5a283a01404a5d46dfd67182406881e55638ad11 Mon Sep 17 00:00:00 2001
From: Stephen Anthony <sa666666@gmail.com>
Date: Sun, 22 Dec 2019 23:33:20 -0330
Subject: [PATCH] Deadcode elimination in M6502 emulation. A minor improvement,
 but every little bit counts.

---
 src/emucore/M6502.cxx |  6 ++--
 src/emucore/M6502.ins | 76 ++++++++++++++++++++++++-------------------
 src/emucore/M6502.m4  | 54 +++++++++++++++++++++++++-----
 3 files changed, 92 insertions(+), 44 deletions(-)

diff --git a/src/emucore/M6502.cxx b/src/emucore/M6502.cxx
index 9ed1feaf6..e75f5bbff 100644
--- a/src/emucore/M6502.cxx
+++ b/src/emucore/M6502.cxx
@@ -328,13 +328,13 @@ inline void M6502::_execute(uInt64 cycles, DispatchResult& result)
       mySystem->cart().clearAllRAMAccesses();
   #endif  // DEBUGGER_SUPPORT
 
-      uInt16 operandAddress = 0, intermediateAddress = 0;
-      uInt8 operand = 0;
-
       // Reset the peek/poke address pointers
       myLastPeekAddress = myLastPokeAddress = myDataAddressForPoke = 0;
 
       try {
+        uInt16 operandAddress = 0, intermediateAddress = 0;
+        uInt8 operand = 0;
+
         icycles = 0;
     #ifdef DEBUGGER_SUPPORT
         uInt16 oldPC = PC;
diff --git a/src/emucore/M6502.ins b/src/emucore/M6502.ins
index 069634e47..97d635509 100644
--- a/src/emucore/M6502.ins
+++ b/src/emucore/M6502.ins
@@ -255,6 +255,16 @@
 
 
 
+
+
+
+
+
+
+
+
+
+
 
 
 
@@ -425,7 +435,7 @@ case 0x7d:
   intermediateAddress = high | uInt8(low + X);
   if((low + X) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + X;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -473,7 +483,7 @@ case 0x79:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -563,7 +573,7 @@ case 0x71:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -697,7 +707,7 @@ case 0x3d:
   intermediateAddress = high | uInt8(low + X);
   if((low + X) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + X;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -720,7 +730,7 @@ case 0x39:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -760,7 +770,7 @@ case 0x31:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -1229,7 +1239,7 @@ case 0xdd:
   intermediateAddress = high | uInt8(low + X);
   if((low + X) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + X;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -1254,7 +1264,7 @@ case 0xd9:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -1298,7 +1308,7 @@ case 0xd1:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -1697,7 +1707,7 @@ case 0x5d:
   intermediateAddress = high | uInt8(low + X);
   if((low + X) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + X;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -1720,7 +1730,7 @@ case 0x59:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -1760,7 +1770,7 @@ case 0x51:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -2209,7 +2219,7 @@ case 0xbb:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -2251,7 +2261,7 @@ case 0xbf:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -2329,7 +2339,7 @@ case 0xb3:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -2413,7 +2423,7 @@ case 0xbd:
   intermediateAddress = high | uInt8(low + X);
   if((low + X) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + X;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -2437,7 +2447,7 @@ case 0xb9:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -2479,7 +2489,7 @@ case 0xb1:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -2561,7 +2571,7 @@ case 0xbe:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -2643,7 +2653,7 @@ case 0xbc:
   intermediateAddress = high | uInt8(low + X);
   if((low + X) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + X;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -2795,7 +2805,7 @@ case 0x89:
 case 0xc2:
 case 0xe2:
 {
-  operand = peek(PC++, DISASM_CODE);
+  peek(PC++, DISASM_CODE);
 }
 {
 }
@@ -2806,7 +2816,7 @@ case 0x44:
 case 0x64:
 {
   intermediateAddress = peek(PC++, DISASM_CODE);
-  operand = peek(intermediateAddress, DISASM_DATA);
+  peek(intermediateAddress, DISASM_DATA);
 }
 {
 }
@@ -2822,7 +2832,7 @@ case 0xf4:
   intermediateAddress = peek(PC++, DISASM_CODE);
   peek(intermediateAddress, DISASM_NONE);
   intermediateAddress += X;
-  operand = peek(intermediateAddress, DISASM_DATA);
+  peek(intermediateAddress, DISASM_DATA);
 }
 {
 }
@@ -2832,7 +2842,7 @@ case 0x0c:
 {
   intermediateAddress = peek(PC++, DISASM_CODE);
   intermediateAddress |= (uInt16(peek(PC++, DISASM_CODE)) << 8);
-  operand = peek(intermediateAddress, DISASM_DATA);
+  peek(intermediateAddress, DISASM_DATA);
 }
 {
 }
@@ -2850,13 +2860,13 @@ case 0xfc:
   intermediateAddress = high | uInt8(low + X);
   if((low + X) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + X;
-    operand = peek(intermediateAddress, DISASM_DATA);
+    peek(intermediateAddress, DISASM_DATA);
   }
   else
   {
-    operand = peek(intermediateAddress, DISASM_DATA);
+    peek(intermediateAddress, DISASM_DATA);
   }
 }
 {
@@ -2927,7 +2937,7 @@ case 0x1d:
   intermediateAddress = high | uInt8(low + X);
   if((low + X) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + X;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -2951,7 +2961,7 @@ case 0x19:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -2993,7 +3003,7 @@ case 0x11:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -3973,7 +3983,7 @@ case 0xfd:
   intermediateAddress = high | uInt8(low + X);
   if((low + X) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + X;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -4018,7 +4028,7 @@ case 0xf9:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -4102,7 +4112,7 @@ case 0xf1:
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
diff --git a/src/emucore/M6502.m4 b/src/emucore/M6502.m4
index ca13e12b3..8f8f57040 100644
--- a/src/emucore/M6502.m4
+++ b/src/emucore/M6502.m4
@@ -61,12 +61,22 @@ define(M6502_IMMEDIATE_READ, `{
   operand = peek(PC++, DISASM_CODE);
 }')
 
+define(M6502_IMMEDIATE_READ_DISCARD_OPERAND, `{
+  peek(PC++, DISASM_CODE);
+}')
+
 define(M6502_ABSOLUTE_READ, `{
   intermediateAddress = peek(PC++, DISASM_CODE);
   intermediateAddress |= (uInt16(peek(PC++, DISASM_CODE)) << 8);
   operand = peek(intermediateAddress, DISASM_DATA);
 }')
 
+define(M6502_ABSOLUTE_READ_DISCARD_OPERAND, `{
+  intermediateAddress = peek(PC++, DISASM_CODE);
+  intermediateAddress |= (uInt16(peek(PC++, DISASM_CODE)) << 8);
+  peek(intermediateAddress, DISASM_DATA);
+}')
+
 define(M6502_ABSOLUTE_WRITE, `{
   operandAddress = peek(PC++, DISASM_CODE);
   operandAddress |= (uInt16(peek(PC++, DISASM_CODE)) << 8);
@@ -85,7 +95,7 @@ define(M6502_ABSOLUTEX_READ, `{
   intermediateAddress = high | uInt8(low + X);
   if((low + X) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + X;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -95,6 +105,22 @@ define(M6502_ABSOLUTEX_READ, `{
   }
 }')
 
+define(M6502_ABSOLUTEX_READ_DISCARD_OPERAND, `{
+  uInt16 low = peek(PC++, DISASM_CODE);
+  uInt16 high = (uInt16(peek(PC++, DISASM_CODE)) << 8);
+  intermediateAddress = high | uInt8(low + X);
+  if((low + X) > 0xFF)
+  {
+    peek(intermediateAddress, DISASM_NONE);
+    intermediateAddress = (high | low) + X;
+    peek(intermediateAddress, DISASM_DATA);
+  }
+  else
+  {
+    peek(intermediateAddress, DISASM_DATA);
+  }
+}')
+
 define(M6502_ABSOLUTEX_WRITE, `{
   uInt16 low = peek(PC++, DISASM_CODE);
   uInt16 high = (uInt16(peek(PC++, DISASM_CODE)) << 8);
@@ -117,7 +143,7 @@ define(M6502_ABSOLUTEY_READ, `{
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -148,6 +174,11 @@ define(M6502_ZERO_READ, `{
   operand = peek(intermediateAddress, DISASM_DATA);
 }')
 
+define(M6502_ZERO_READ_DISCARD_OPERAND, `{
+  intermediateAddress = peek(PC++, DISASM_CODE);
+  peek(intermediateAddress, DISASM_DATA);
+}')
+
 define(M6502_ZERO_WRITE, `{
   operandAddress = peek(PC++, DISASM_CODE);
 }')
@@ -165,6 +196,13 @@ define(M6502_ZEROX_READ, `{
   operand = peek(intermediateAddress, DISASM_DATA);
 }')
 
+define(M6502_ZEROX_READ_DISCARD_OPERAND, `{
+  intermediateAddress = peek(PC++, DISASM_CODE);
+  peek(intermediateAddress, DISASM_NONE);
+  intermediateAddress += X;
+  peek(intermediateAddress, DISASM_DATA);
+}')
+
 define(M6502_ZEROX_WRITE, `{
   operandAddress = peek(PC++, DISASM_CODE);
   peek(operandAddress, DISASM_NONE);
@@ -245,7 +283,7 @@ define(M6502_INDIRECTY_READ, `{
   intermediateAddress = high | uInt8(low + Y);
   if((low + Y) > 0xFF)
   {
-    operand = peek(intermediateAddress, DISASM_NONE);
+    peek(intermediateAddress, DISASM_NONE);
     intermediateAddress = (high | low) + Y;
     operand = peek(intermediateAddress, DISASM_DATA);
   }
@@ -1750,14 +1788,14 @@ case 0x82:
 case 0x89:
 case 0xc2:
 case 0xe2:
-M6502_IMMEDIATE_READ
+M6502_IMMEDIATE_READ_DISCARD_OPERAND
 M6502_NOP
 break;
 
 case 0x04:
 case 0x44:
 case 0x64:
-M6502_ZERO_READ
+M6502_ZERO_READ_DISCARD_OPERAND
 M6502_NOP
 break;
 
@@ -1767,12 +1805,12 @@ case 0x54:
 case 0x74:
 case 0xd4:
 case 0xf4:
-M6502_ZEROX_READ
+M6502_ZEROX_READ_DISCARD_OPERAND
 M6502_NOP
 break;
 
 case 0x0c:
-M6502_ABSOLUTE_READ
+M6502_ABSOLUTE_READ_DISCARD_OPERAND
 M6502_NOP
 break;
 
@@ -1782,7 +1820,7 @@ case 0x5c:
 case 0x7c:
 case 0xdc:
 case 0xfc:
-M6502_ABSOLUTEX_READ
+M6502_ABSOLUTEX_READ_DISCARD_OPERAND
 M6502_NOP
 break;