More BYTE REGISTER fixes.

internal/optimizer/optimizer_test.go

@@ -1069,3 +1069,46 @@ func TestPassRegDead_ReadModifyWrite(t *testing.T) {
 		})
 	}
 }
+
+func TestPassRegDead_JmpDoesNotKillStore(t *testing.T) {
+	// sta regVar; ...(then body)...; jmp _END; _ELSE:; ...; _END:; ldy regVar
+	// The jmp in the THEN body should NOT kill the store because
+	// the jump target _END reaches code that reads regVar.
+	input := []string{
+		"\tldy #0",
+		"\tlda (zp),y",
+		"\tsta if_val",
+		"\tlda test_i",
+		"\tcmp #$06",
+		"\tbne _I1",
+		"\tlda (zp),y",
+		"\tsta other",
+		"\tjmp _I2",
+		"_I1",
+		"\tldy #1",
+		"\tlda (zp),y",
+		"\tsta other",
+		"_I2",
+		"\tldy if_val",
+		"\tlda (zp),y",
+		"\trts",
+	}
+
+	cfg := &Config{
+		EnableRegisterVars: true,
+		RegisterVars: map[string]bool{
+			"if_val": true,
+		},
+	}
+
+	output, dissolved := Optimize(input, cfg)
+
+	if dissolved["if_val"] {
+		t.Error("if_val should NOT be dissolved — ldy if_val reads its value")
+	}
+
+	joined := strings.Join(output, "\n")
+	if !strings.Contains(joined, "sta if_val") {
+		t.Errorf("expected sta if_val to be kept (jmp in THEN should not kill it), got:\n%s", joined)
+	}
+}

internal/optimizer/pass_regdead.go

@@ -60,7 +60,7 @@ func isRegStoreDead(lines []asmLine, start int, operand string) bool {
 		}
 
 		if l.isCode && blocksFlow(l) {
-			return true // rts/jmp/brk/rti — execution ends here
+			return true // rts/brk/rti — execution ends here
 		}
 
 		if l.isCode && readsFrom(l.opcode, l.operand, operand) {
@@ -93,7 +93,7 @@ func readsFrom(opcode, operand, varName string) bool {
 // execution path: rts, jmp, brk, rti
 func blocksFlow(line asmLine) bool {
 	switch line.opcode {
-	case "rts", "jmp", "brk", "rti":
+	case "rts", "brk", "rti":
 		return true
 	}
 	return false