VarAction2: Detect equality comparisons

Remove redundant equality with 0 comparison before ternary

src/newgrf.cpp

@@ -5666,6 +5666,15 @@ static void NewSpriteGroup(ByteReader *buf)
 									if (adjust.and_mask <= 1) inference = VA2AIF_SIGNED_NON_NEGATIVE | VA2AIF_ONE_OR_ZERO;
 									break;
 								case DSGA_OP_AND:
+									if ((prev_inference & VA2AIF_SIGNED_NON_NEGATIVE) && adjust.variable == 0x1A && adjust.shift_num == 0 && adjust.and_mask == 1) {
+										DeterministicSpriteGroupAdjust &prev = group->adjusts[group->adjusts.size() - 2];
+										if (prev.operation == DSGA_OP_SCMP || prev.operation == DSGA_OP_UCMP) {
+											prev.operation = DSGA_OP_EQ;
+											group->adjusts.pop_back();
+											inference = VA2AIF_SIGNED_NON_NEGATIVE | VA2AIF_ONE_OR_ZERO;
+											break;
+										}
+									}
 									if (adjust.and_mask <= 1) {
 										inference = VA2AIF_SIGNED_NON_NEGATIVE | VA2AIF_ONE_OR_ZERO;
 									} else if ((adjust.and_mask & (1 << ((varsize * 8) - 1))) == 0) {
@@ -5700,6 +5709,17 @@ static void NewSpriteGroup(ByteReader *buf)
 											}
 											break;
 										}
+										if (group->adjusts.size() > 1) {
+											/* Remove redundant comparison with 0 if applicable */
+											const DeterministicSpriteGroupAdjust &prev = group->adjusts[group->adjusts.size() - 2];
+											if (prev.type == DSGA_TYPE_NONE && prev.operation == DSGA_OP_EQ && prev.variable == 0x1A && prev.shift_num == 0 && prev.and_mask == 0) {
+												DeterministicSpriteGroupAdjust current = group->adjusts.back();
+												group->adjusts.pop_back();
+												group->adjusts.pop_back();
+												std::swap(current.and_mask, current.add_val);
+												group->adjusts.push_back(current);
+											}
+										}
 										inference = VA2AIF_PREV_TERNARY;
 									}
 									break;

src/newgrf_spritegroup.cpp

@@ -183,6 +183,7 @@ static U EvalAdjustT(const DeterministicSpriteGroupAdjust &adjust, ScopeResolver
 		case DSGA_OP_SHR:  return (uint32)(U)last_value >> ((U)value & 0x1F);
 		case DSGA_OP_SAR:  return (int32)(S)last_value >> ((U)value & 0x1F);
 		case DSGA_OP_TERNARY: return (last_value != 0) ? value : adjust.add_val;
+		case DSGA_OP_EQ:   return (last_value == value) ? 1 : 0;
 		default:           return value;
 	}
 }
@@ -562,6 +563,14 @@ static const char *_sg_size_names[] {
 	"DWORD",
 };
 
+static const char *GetAdjustOperationName(DeterministicSpriteGroupAdjustOperation operation)
+{
+	if (operation < DSGA_OP_END) return _dsg_op_names[operation];
+	if (operation == DSGA_OP_TERNARY) return "TERNARY";
+	if (operation == DSGA_OP_EQ) return "EQ";
+	return "???";
+}
+
 void SpriteGroupDumper::DumpSpriteGroup(const SpriteGroup *sg, int padding, uint flags)
 {
 	if (sg == nullptr) {
@@ -634,7 +643,7 @@ void SpriteGroupDumper::DumpSpriteGroup(const SpriteGroup *sg, int padding, uint
 					case DSGA_TYPE_MOD:  p += seprintf(p, lastof(this->buffer), ", add: %X, mod: %X", adjust.add_val, adjust.divmod_val); break;
 					case DSGA_TYPE_NONE: break;
 				}
-				p += seprintf(p, lastof(this->buffer), ", op: %X (%s)", adjust.operation, adjust.operation < DSGA_OP_END ? _dsg_op_names[adjust.operation] : "???");
+				p += seprintf(p, lastof(this->buffer), ", op: %X (%s)", adjust.operation, GetAdjustOperationName(adjust.operation));
 				this->print();
 			}
 			if (dsg->calculated_result) {

src/newgrf_spritegroup.h

@@ -163,6 +163,7 @@ enum DeterministicSpriteGroupAdjustOperation {
 	DSGA_OP_END,
 
 	DSGA_OP_TERNARY = 0x80, ///< a == 0 ? b : c,
+	DSGA_OP_EQ,             ///< a == b ? 1 : 0,
 
 	DSGA_OP_SPECIAL_END,
 };