VarAction2: Add an ABS opcode

src/newgrf.cpp

@@ -5633,8 +5633,9 @@ enum VarAction2AdjustInferenceFlags {
 	VA2AIF_HAVE_CONSTANT         = 0x20,
 	VA2AIF_SINGLE_LOAD           = 0x40,
 	VA2AIF_MUL_BOOL              = 0x80,
+	VA2AIF_PREV_SCMP_DEC         = 0x100,
 
-	VA2AIF_PREV_MASK             = VA2AIF_PREV_TERNARY | VA2AIF_PREV_MASK_ADJUST | VA2AIF_PREV_STORE_TMP,
+	VA2AIF_PREV_MASK             = VA2AIF_PREV_TERNARY | VA2AIF_PREV_MASK_ADJUST | VA2AIF_PREV_STORE_TMP | VA2AIF_PREV_SCMP_DEC,
 };
 DECLARE_ENUM_AS_BIT_SET(VarAction2AdjustInferenceFlags)
 
@@ -6322,6 +6323,12 @@ static void OptimiseVarAction2Adjust(VarAction2OptimiseState &state, const GrfSp
 							}
 						}
 					}
+					if (adjust.variable == 0x1A && adjust.shift_num == 0 && adjust.and_mask == 1 && group->adjusts.size() >= 2) {
+						DeterministicSpriteGroupAdjust &prev = group->adjusts[group->adjusts.size() - 2];
+						if (prev.operation == DSGA_OP_SCMP) {
+							state.inference |= VA2AIF_PREV_SCMP_DEC;
+						}
+					}
 					try_merge_with_previous();
 					break;
 				case DSGA_OP_SMIN:
@@ -6543,6 +6550,23 @@ static void OptimiseVarAction2Adjust(VarAction2OptimiseState &state, const GrfSp
 						state.inference = VA2AIF_PREV_TERNARY;
 						break;
 					}
+					if ((prev_inference & VA2AIF_PREV_SCMP_DEC) && group->adjusts.size() >= 4 && adjust.variable == 0x7D && adjust.shift_num == 0 && adjust.and_mask == 0xFFFFFFFF) {
+						const DeterministicSpriteGroupAdjust &adj1 = group->adjusts[group->adjusts.size() - 4];
+						const DeterministicSpriteGroupAdjust &adj2 = group->adjusts[group->adjusts.size() - 3];
+						const DeterministicSpriteGroupAdjust &adj3 = group->adjusts[group->adjusts.size() - 2];
+						auto is_expected_op = [](const DeterministicSpriteGroupAdjust &adj, DeterministicSpriteGroupAdjustOperation op, uint32 value) -> bool {
+							return adj.operation == op && adj.type == DSGA_TYPE_NONE && adj.variable == 0x1A && adj.shift_num == 0 && adj.and_mask == value;
+						};
+						if (is_expected_op(adj1, DSGA_OP_STO, (adjust.parameter & 0xFF)) &&
+								is_expected_op(adj2, DSGA_OP_SCMP, 0) &&
+								is_expected_op(adj3, DSGA_OP_SUB, 1)) {
+							group->adjusts.pop_back();
+							group->adjusts.pop_back();
+							group->adjusts.back().operation = DSGA_OP_ABS;
+							state.inference |= VA2AIF_SIGNED_NON_NEGATIVE;
+							break;
+						}
+					}
 					uint32 sign_bit = (1 << ((varsize * 8) - 1));
 					if ((prev_inference & VA2AIF_PREV_MASK_ADJUST) && (prev_inference & VA2AIF_SIGNED_NON_NEGATIVE) && adjust.variable == 0x1A && adjust.shift_num == 0 && (adjust.and_mask & sign_bit) == 0) {
 						/* Determine whether the result will be always non-negative */

src/newgrf_spritegroup.cpp

@@ -200,6 +200,7 @@ static U EvalAdjustT(const DeterministicSpriteGroupAdjust &adjust, ScopeResolver
 		case DSGA_OP_SGT:  return ((S)last_value >  (S)value) ? 1 : 0;
 		case DSGA_OP_RSUB: return value - last_value;
 		case DSGA_OP_STO_NC: _temp_store.StoreValue(adjust.divmod_val, (S)value); return last_value;
+		case DSGA_OP_ABS:  return ((S)last_value < 0) ? -((S)last_value) : (S)last_value;
 		default:           return value;
 	}
 }
@@ -683,6 +684,7 @@ static const char *_dsg_op_special_names[] {
 	"SGT",
 	"RSUB",
 	"STO_NC",
+	"ABS",
 };
 static_assert(lengthof(_dsg_op_special_names) == DSGA_OP_SPECIAL_END - DSGA_OP_TERNARY);
 
@@ -727,6 +729,11 @@ static char *DumpSpriteGroupAdjust(char *p, const char *last, const Deterministi
 		append_flags();
 		return p;
 	}
+	if (adjust.operation == DSGA_OP_ABS) {
+		p += seprintf(p, last, "%*sABS", padding, "");
+		append_flags();
+		return p;
+	}
 	if (adjust.operation == DSGA_OP_STO && adjust.type == DSGA_TYPE_NONE && adjust.variable == 0x1A && adjust.shift_num == 0) {
 		/* Temp storage store */
 		highlight_tag = (1 << 16) | (adjust.and_mask & 0xFFFF);

src/newgrf_spritegroup.h

@@ -198,6 +198,7 @@ enum DeterministicSpriteGroupAdjustOperation : uint8 {
 	DSGA_OP_SGT,            ///< (signed) a > b ? 1 : 0,
 	DSGA_OP_RSUB,           ///< b - a
 	DSGA_OP_STO_NC,         ///< store b into temporary storage, indexed by c. return a
+	DSGA_OP_ABS,            ///< abs(a)
 
 	DSGA_OP_SPECIAL_END,
 };