Enable GCC implicit fallthrough warning.

I've guessed whether break or [[fallthrough]] is appropriate.  In cases
where it looked particularly suspicious, I added a FIXME comment.  All
of these changes should be reviewed by someone familiar with the code.

scripts/genie.lua

@@ -1078,6 +1078,12 @@ end
 				print("GCC version 7.0 or later needed")
 				os.exit(-1)
 			end
+				buildoptions_cpp {
+					"-Wimplicit-fallthrough",
+				}
+				buildoptions_objcpp {
+					"-Wimplicit-fallthrough",
+				}
 				buildoptions {
 					"-Wno-unused-result", -- needed for fgets,fread on linux
 					-- array bounds checking seems to be buggy in 4.8.1 (try it on video/stvvdp1.c and video/model1.c without -Wno-array-bounds)

scripts/src/3rdparty.lua

@@ -225,6 +225,11 @@ configuration { "gmake or ninja" }
 buildoptions_cpp {
 	"-x c++",
 }
+if _OPTIONS["gcc"]~=nil and not string.find(_OPTIONS["gcc"], "clang") then
+	buildoptions_cpp {
+		"-Wno-error=implicit-fallthrough",
+	}
+end
 
 configuration { "vs*" }
 buildoptions {

src/devices/bus/ata/atapicdr.cpp

@@ -130,6 +130,7 @@ void atapi_cdrom_device::ExecCommand()
 				m_transfer_length = 0;
 				return;
 			}
+			[[fallthrough]];
 		default:
 			if(m_media_change)
 			{

src/devices/bus/bbc/fdc/opus.cpp

@@ -230,6 +230,7 @@ uint8_t bbc_opus8272_device::read(offs_t offset)
 	case 0x06:
 		if (m_floppy0->get_device()) m_floppy0->get_device()->mon_w(1);
 		if (m_floppy1->get_device()) m_floppy1->get_device()->mon_w(1);
+		[[fallthrough]];
 	case 0x04:
 		data = m_fdc->msr_r();
 		break;
@@ -237,6 +238,7 @@ uint8_t bbc_opus8272_device::read(offs_t offset)
 	case 0x05:
 		if (m_floppy0->get_device()) m_floppy0->get_device()->mon_w(0);
 		if (m_floppy1->get_device()) m_floppy1->get_device()->mon_w(0);
+		[[fallthrough]];
 	case 0x07:
 		data = m_fdc->fifo_r();
 		break;
@@ -262,6 +264,7 @@ void bbc_opus8272_device::write(offs_t offset, uint8_t data)
 	case 0x05:
 		if (m_floppy0->get_device()) m_floppy0->get_device()->mon_w(0);
 		if (m_floppy1->get_device()) m_floppy1->get_device()->mon_w(0);
+		[[fallthrough]];
 	case 0x07:
 		m_fdc->fifo_w(data);
 		break;

src/devices/bus/electron/plus2.cpp

@@ -126,6 +126,7 @@ uint8_t electron_plus2_device::expbus_r(offs_t offset)
 		case 13:
 			data &= m_cart[0]->read(offset & 0x3fff, 0, 0, m_romsel & 0x01, 0, 1);
 			data &= m_cart[1]->read(offset & 0x3fff, 0, 0, m_romsel & 0x01, 0, 1);
+			[[fallthrough]];
 		case 14:
 		case 15:
 			data &= m_rom[m_romsel - 13]->read_rom(offset & 0x3fff);

src/devices/bus/electron/romboxp.cpp

@@ -201,6 +201,7 @@ uint8_t electron_romboxp_device::expbus_r(offs_t offset)
 		case 13:
 			data &= m_cart[0]->read(offset & 0x3fff, 0, 0, m_romsel & 0x01, 0, 1);
 			data &= m_cart[1]->read(offset & 0x3fff, 0, 0, m_romsel & 0x01, 0, 1);
+			[[fallthrough]];
 		case 14:
 		case 15:
 			if (m_rom_base == 12)
@@ -274,6 +275,7 @@ void electron_romboxp_device::expbus_w(offs_t offset, uint8_t data)
 		case 13:
 			m_cart[0]->write(offset & 0x3fff, data, 0, 0, m_romsel & 0x01, 0, 1);
 			m_cart[1]->write(offset & 0x3fff, data, 0, 0, m_romsel & 0x01, 0, 1);
+			[[fallthrough]];
 		case 14:
 		case 15:
 			if (m_rom_base == 12)

src/devices/bus/gameboy/rom.cpp

@@ -220,6 +220,7 @@ void gb_rom_tama5_device::write_ram(offs_t offset, uint8_t data)
 				case 0x40:      /* Unknown, some kind of read */
 					if ((m_tama5_addr & 0x1f) == 0x12)
 						m_tama5_data = 0xff;
+					[[fallthrough]];
 				case 0x80:      /* Unknown, some kind of read (when 07=01)/write (when 07=00/02) */
 				default:
 					logerror( "%s Unknown addressing mode\n", machine().describe_context() );

src/devices/bus/gba/rom.cpp

@@ -301,6 +301,7 @@ uint32_t gba_rom_device::read_gpio(offs_t offset, uint32_t mem_mask)
 				}
 				if (ACCESSING_BITS_16_31)
 					return m_gpio_regs[1] << 16;
+				[[fallthrough]];
 			case 1:
 				if (ACCESSING_BITS_0_15)
 					return m_gpio_regs[2];

src/devices/bus/isa/3c503.cpp

@@ -245,6 +245,7 @@ void el2_3c503_device::el2_3c503_hiport_w(offs_t offset, uint8_t data) {
 		default:
 			logerror("3c503: trying to set multiple drqs %X\n", data);
 		}
+		break;
 	case 9:
 		if(m_regs.ctrl & 0x80) logerror("3c503: changing dma address during dma is undefined\n");
 		m_regs.da = (data << 8) | (m_regs.da & 0xff);

src/devices/bus/isa/gus.cpp

@@ -502,6 +502,7 @@ uint8_t gf1_device::global_reg_data_r(offs_t offset)
 			m_dma_irq_handler(0);
 			return ret;
 		}
+		break;
 	case 0x45:  // Timer control
 		if(offset == 1)
 			return m_timer_ctrl & 0x0c;
@@ -509,15 +510,18 @@ uint8_t gf1_device::global_reg_data_r(offs_t offset)
 	case 0x49:  // Sampling control
 		if(offset == 1)
 			return m_sampling_ctrl & 0xe7;
+		break;
 	case 0x4c:  // Reset
 		if(offset == 1)
 			return m_reset;
+		break;
 	case 0x80: // Voice control
 /* bit 0 - 1 if voice is stopped
  * bit 6 - 1 if addresses are decreasing, can change when looping is enabled
  * bit 7 - 1 if Wavetable IRQ is pending */
 		if(offset == 1)
 			return m_voice[m_current_voice].voice_ctrl & 0xff;
+		break;
 	case 0x81:  // Frequency Control
 		ret = m_voice[m_current_voice].freq_ctrl;
 		if(offset == 0)
@@ -551,12 +555,15 @@ uint8_t gf1_device::global_reg_data_r(offs_t offset)
 	case 0x86:  // Volume Ramp rate
 		if(offset == 1)
 			return m_voice[m_current_voice].vol_ramp_rate;
+		break;
 	case 0x87:  // Volume Ramp start (high 4 bits = exponent, low 4 bits = mantissa)
 		if(offset == 1)
 			return m_voice[m_current_voice].vol_ramp_start;
+		break;
 	case 0x88:  // Volume Ramp end (high 4 bits = exponent, low 4 bits = mantissa)
 		if(offset == 1)
 			return m_voice[m_current_voice].vol_ramp_end;
+		break;
 	case 0x89:  // Current Volume (high 4 bits = exponent, middle 8 bits = mantissa, low 4 bits = 0 [reserved])
 		ret = m_voice[m_current_voice].current_vol;
 		if(offset == 0)
@@ -578,15 +585,18 @@ uint8_t gf1_device::global_reg_data_r(offs_t offset)
 	case 0x8c:  // Pan position (4 bits, 0=full left, 15=full right)
 		if(offset == 1)
 			return m_voice[m_current_voice].pan_position;
+		break;
 	case 0x8d:  // Volume Ramp control
 /* bit 0 - Ramp has stopped
  * bit 6 - Ramp direction
  * bit 7 - Ramp IRQ pending */
 		if(offset == 1)
 			return m_voice[m_current_voice].vol_ramp_ctrl;
+		break;
 	case 0x8e:  // Active voices (6 bits, high 2 bits are always 1)
 		if(offset == 1)
 			return (m_active_voices - 1) | 0xc0;
+		break;
 	case 0x8f:  // IRQ source register
 		if(offset == 1)
 		{

src/devices/bus/isa/mcd.cpp

@@ -224,6 +224,7 @@ void mcd_isa_device::cmd_w(uint8_t data)
 				{
 					case 5:
 						m_readmsf = 0;
+						[[fallthrough]];
 					case 4:
 					case 3:
 						m_readmsf |= bcd_2_dec(data) << ((m_cmdrd_count - 3) * 8);

src/devices/bus/isa/myb3k_fdc.cpp

@@ -194,8 +194,10 @@ WRITE_LINE_MEMBER( isa8_myb3k_fdc471x_device_base::drq_w )
 	{
 	case 1:
 		m_isa->drq1_w(state);
+		[[fallthrough]]; // FIXME: really?
 	case 2:
 		m_isa->drq2_w(state);
+		[[fallthrough]]; // FIXME: really?
 	default:
 		break;
 	}

src/devices/bus/isa/sblaster.cpp

@@ -556,6 +556,7 @@ void sb_device::process_fifo(uint8_t cmd)
 					{
 						case 0x0f:  // read asp reg
 							queue_r(0);
+							[[fallthrough]];
 						case 0x0e:  // write asp reg
 						case 0x02:  // get asp version
 						case 0x04:  // set asp mode register

src/devices/bus/nes/cony.cpp

@@ -237,6 +237,7 @@ void nes_cony_device::write_h(offs_t offset, uint8_t data)
 	{
 		case 0x0000:
 			m_latch1 = 1;
+			[[fallthrough]];
 		case 0x3000:
 		case 0x30ff:
 		case 0x31ff:
@@ -283,6 +284,7 @@ void nes_cony_device::write_h(offs_t offset, uint8_t data)
 		case 0x0314:
 		case 0x0315:
 			m_latch2 = 1;
+			[[fallthrough]];
 		case 0x0310:
 		case 0x0311:
 		case 0x0316:

src/devices/bus/nes/mmc3_clones.cpp

@@ -775,6 +775,7 @@ void nes_pikay2k_device::write_h(offs_t offset, uint8_t data)
 
 		case 0x2000:
 			m_reg[0] = 0;
+			[[fallthrough]];
 		default:
 			txrom_write(offset, data);
 			break;

src/devices/bus/nes/multigame.cpp

@@ -1770,6 +1770,7 @@ void nes_bmc_ball11_device::write_h(offs_t offset, uint8_t data)
 	{
 		case 0x4000:    // here we also update reg[0] upper bit
 			m_reg[0] = (m_reg[0] & 0x01) | ((data >> 3) & 0x02);
+			[[fallthrough]];
 		case 0x0000:
 		case 0x2000:
 		case 0x6000:

src/devices/bus/nes/namcot.cpp

@@ -454,10 +454,12 @@ uint8_t nes_namcot340_device::n340_loread(offs_t offset)
 	{
 		case 0x1000:
 			return m_irq_count & 0xff;
-			set_irq_line(CLEAR_LINE);
+			set_irq_line(CLEAR_LINE); // FIXME: unreachable
+			[[fallthrough]];
 		case 0x1800:
 			return (m_irq_count >> 8) & 0xff;
-			set_irq_line(CLEAR_LINE);
+			set_irq_line(CLEAR_LINE); // FIXME: unreachable
+			[[fallthrough]];
 		default:
 			return 0x00;
 	}

src/devices/bus/nes/nes_ines.hxx

@@ -372,6 +372,7 @@ void nes_cart_slot_device::call_load_ines()
 
 		case 0x8:   // it's iNES 2.0 format
 			ines20 = true;
+			[[fallthrough]];
 		case 0x0:
 		default:
 			mapper |= header[7] & 0xf0;
@@ -840,6 +841,7 @@ const char * nes_cart_slot_device::get_default_card_ines(get_default_card_softwa
 
 		case 0x8:   // it's iNES 2.0 format
 			ines20 = true;
+			[[fallthrough]];
 		case 0x0:
 		default:
 			mapper |= ROM[7] & 0xf0;

src/devices/bus/nes/pirate.cpp

@@ -1204,7 +1204,7 @@ void nes_cityfight_device::write_h(offs_t offset, uint8_t data)
 		case 0x4008:
 		case 0x400c:
 			m_prg_mode = data & 1;
-
+			[[fallthrough]];
 		case 0x7000:
 			m_irq_count = (m_irq_count & 0x1e0) | ((data & 0x0f) << 1);
 			break;

src/devices/bus/pce/pce_rom.cpp

@@ -214,6 +214,7 @@ void pce_tennokoe_device::write_cart(offs_t offset, uint8_t data)
 			// TODO: lock/unlock mechanism is a complete guess, needs real HW study
 			// (writes to ports $c0000, $d0000, $f0000)
 			m_bram_locked = (data == 0);
+			[[fallthrough]];
 		default:
 			logerror("tennokoe: ROM writing at %06x %02x\n",offset,data);
 			break;

src/devices/bus/sunmouse/hlemouse.cpp

@@ -229,6 +229,7 @@ void hle_device_base::tra_complete()
 					m_y_delta);
 			//break; uncommenting this causes problems with early versions of Solaris
 		}
+		[[fallthrough]];
 	case 1U:
 		LOG("Sent %s (B=%X->%x X=%d Y=%d) - sending X delta\n",
 				(1U == m_phase) ? "button state" : "Y delta",

src/devices/bus/vcs/dpc.cpp

@@ -128,6 +128,7 @@ uint8_t dpc_device::read(offs_t offset)
 				return m_shift_reg;
 			case 0x04:      // Sound value, MOVAMT value AND'd with Draw Line Carry; with Draw Line Add
 				m_latch_62 = m_latch_64;
+				[[fallthrough]];
 			case 0x06:      // Sound value, MOVAMT value AND'd with Draw Line Carry; without Draw Line Add
 				m_latch_64 = m_latch_62 + m_df[4].top;
 				m_dlc = (m_latch_62 + m_df[4].top > 0xff) ? 1 : 0;

src/devices/bus/wswan/rom.cpp

@@ -360,6 +360,7 @@ void ws_rom_sram_device::write_io(offs_t offset, uint8_t data)
 	{
 		case 0x01:  // SRAM bank to select
 			m_nvram_base = (data * 0x10000) & (m_nvram.size() -  1);
+			[[fallthrough]];
 		default:
 			ws_rom_device::write_io(offset, data);
 			break;

src/devices/cpu/bcp/dp8344.cpp

@@ -1831,7 +1831,7 @@ void dp8344_device::store_result()
 			write_register(m_latched_instr & 0x001f, m_source_data);
 			break;
 		}
-
+		[[fallthrough]]; // FIXME: really?
 	case 0xe000:
 		if (BIT(m_latched_instr, 11))
 			m_source_data = sub_nzcv(m_source_data, read_accumulator(), BIT(m_latched_instr, 10) && BIT(m_ccr, 1));

src/devices/cpu/ccpu/ccpu.cpp

@@ -599,6 +599,7 @@ void ccpu_cpu_device::execute_run()
 			/* CST */
 			case 0xf7:
 				m_watchdog = 0;
+				[[fallthrough]];
 			/* ADDP */
 			case 0xe7:
 				tempval = RDMEM(m_I);

src/devices/cpu/cosmac/cosmac.cpp

@@ -860,7 +860,7 @@ inline void cosmac_device::run_state()
 	{
 	case cosmac_state::STATE_0_FETCH:
 		m_op = 0;
-
+		[[fallthrough]];
 	case cosmac_state::STATE_0_FETCH_2ND:
 		fetch_instruction();
 		break;
@@ -872,7 +872,7 @@ inline void cosmac_device::run_state()
 
 	case cosmac_state::STATE_1_EXECUTE:
 		sample_ef_lines();
-
+		[[fallthrough]];
 	case cosmac_state::STATE_1_EXECUTE_2ND:
 		execute_instruction();
 		debug();

src/devices/cpu/dspp/dspp.cpp

@@ -613,10 +613,11 @@ inline void dspp_device::set_rbase(uint32_t base, uint32_t addr)
 		case 0:
 			m_core->m_rbase[0] = addr;
 			m_core->m_rbase[1] = addr + 4 - base;
+			[[fallthrough]];
 		// Intentional fall-through
 		case 8:
 			m_core->m_rbase[2] = addr + 8 - base;
-
+			[[fallthrough]];
 		case 12:
 			m_core->m_rbase[3] = addr + 12 - base;
 			break;

src/devices/cpu/dspp/dsppfe.cpp

@@ -86,11 +86,11 @@ bool dspp_frontend::describe(opcode_desc &desc, const opcode_desc *prev)
 		{
 			case 0:
 				describe_special(op, desc);
-
+				[[fallthrough]]; // FIXME: really?
 			case 1:
 			case 2:
 				describe_branch(op, desc);
-
+				[[fallthrough]]; // FIXME: really?
 			case 3:
 				describe_complex_branch(op, desc);
 		}

src/devices/cpu/i8089/i8089_dasm.cpp

@@ -362,7 +362,6 @@ std::string i8089_disassembler::do_disassemble()
 			else if (m_wb == 2)
 				return util::string_format("lcall %s, %05x", off, m_pc + (int16_t) i);
 		}
-		else
 		return invalid();
 
 	case 0x28: return inst_rm("addb", "add");

src/devices/cpu/i86/i286.cpp

@@ -850,6 +850,7 @@ void i80286_cpu_device::code_descriptor(uint16_t selector, uint16_t offset, int
 					if (SEGDESC(r) || (GATE(r) != TSSDESCIDLE))
 						throw TRAP(FAULT_GP,IDXTBL(selector));
 
+					[[fallthrough]];
 				case TSSDESCIDLE:
 					switch_task(selector, gate);
 					load_flags(CompressFlags(), CPL);
@@ -1888,7 +1889,7 @@ reg.base = BASE(desc); (void)(r); reg.limit = LIMIT(desc); }
 						break;
 					}
 				}
-
+				[[fallthrough]];
 				default:
 					if(!common_op(op))
 					{

src/devices/cpu/m68000/m68kfpu.cpp

@@ -1748,7 +1748,7 @@ void m68000_base_device::fmovem(u16 w2)
 			case 1: // Dynamic register list, postincrement or control addressing mode.
 				// FIXME: not really tested, but seems to work
 				reglist = REG_D()[(reglist >> 4) & 7];
-
+				[[fallthrough]];
 			case 0:     // Static register list, predecrement or control addressing mode
 			{
 				for (i=0; i < 8; i++)
@@ -1807,7 +1807,7 @@ void m68000_base_device::fmovem(u16 w2)
 			case 3: // Dynamic register list, predecrement addressing mode.
 				// FIXME: not really tested, but seems to work
 				reglist = REG_D()[(reglist >> 4) & 7];
-
+				[[fallthrough]];
 			case 2:     // Static register list, postincrement or control addressing mode
 			{
 				for (i=0; i < 8; i++)

src/devices/cpu/m68000/m68kmmu.h

@@ -1050,6 +1050,7 @@ void m68851_pmove_put(u32 ea, u16 modes)
 			pmmu_atc_flush();
 		}
 	}
+	[[fallthrough]];
 	case 1:
 		logerror("680x0: unknown PMOVE case 1, PC %x\n", m_pc);
 		break;

src/devices/cpu/mips/mips3.cpp

@@ -5211,6 +5211,7 @@ void mips3_device::execute_run()
 						machine().debug_break();
 					break;
 				}
+				[[fallthrough]];
 			case 0x31:  /* LWC1 */
 				if (!(SR & SR_COP1))
 				{
@@ -5233,6 +5234,7 @@ void mips3_device::execute_run()
 						machine().debug_break();
 					break;
 				}
+				[[fallthrough]];
 			case 0x35:  /* LDC1 */
 				if (!(SR & SR_COP1))
 				{

src/devices/cpu/mips/mips3fe.cpp

@@ -155,6 +155,7 @@ bool mips3_frontend::describe(opcode_desc &desc, const opcode_desc *prev)
 		case 0x22:  // LWL
 		case 0x26:  // LWR
 			desc.regin[0] |= REGFLAG_R(RTREG);
+			[[fallthrough]];
 		case 0x20:  // LB
 		case 0x21:  // LH
 		case 0x23:  // LW

src/devices/cpu/mips/r4000.cpp

@@ -978,7 +978,7 @@ void r4000_base_device::cpu_execute(u32 const op)
 				m_icache_tag[(ADDR(m_r[RSREG], s16(op)) & m_icache_mask_hi) >> m_icache_shift] &= ~ICACHE_V;
 				break;
 			}
-
+			[[fallthrough]];
 		case 0x04: // index load tag (I)
 			if (ICACHE)
 			{
@@ -989,7 +989,7 @@ void r4000_base_device::cpu_execute(u32 const op)
 
 				break;
 			}
-
+			[[fallthrough]];
 		case 0x08: // index store tag (I)
 			if (ICACHE)
 			{
@@ -999,7 +999,7 @@ void r4000_base_device::cpu_execute(u32 const op)
 
 				break;
 			}
-
+			[[fallthrough]];
 		case 0x01: // index writeback invalidate (D)
 		case 0x02: // index invalidate (SI)
 		case 0x03: // index writeback invalidate (SD)
@@ -1891,6 +1891,7 @@ void r5000_device::cp1_execute(u32 const op)
 				return;
 			}
 		}
+		[[fallthrough]];
 		case 0x11: // D
 			switch (op & 0x3f)
 			{

src/devices/cpu/pdp1/pdp1.cpp

@@ -551,6 +551,7 @@ void pdp1_device::device_start()
 	{
 	default:
 		m_extend_support = 0;
+		[[fallthrough]];
 	case 0:     /* no extension */
 		m_extended_address_mask = 07777;
 		m_address_extension_mask = 00000;

src/devices/cpu/powerpc/ppcfe.cpp

@@ -711,6 +711,7 @@ bool ppc_device::frontend::describe_1f(uint32_t op, opcode_desc &desc, const opc
 		case 0x136: // ECIWX
 			if (!(m_ppc.m_cap & PPCCAP_VEA))
 				return false;
+			[[fallthrough]];
 		case 0x014: // LWARX
 		case 0x017: // LWZX
 		case 0x057: // LBZX
@@ -920,6 +921,7 @@ bool ppc_device::frontend::describe_1f(uint32_t op, opcode_desc &desc, const opc
 		case 0x1b6: // ECOWX
 			if (!(m_ppc.m_cap & PPCCAP_VEA))
 				return false;
+			[[fallthrough]];
 		case 0x096: // STWCX.
 		case 0x097: // STWX
 		case 0x0d7: // STBX
@@ -1339,6 +1341,7 @@ bool ppc_device::frontend::describe_3f(uint32_t op, opcode_desc &desc, const opc
 			case 0x00e: // FCTIWx
 			case 0x00f: // FCTIWZx
 				FPSCR_MODIFIED(desc, 4);
+				[[fallthrough]];
 			case 0x028: // FNEGx
 			case 0x048: // FMRx
 			case 0x088: // FNABSx

src/devices/cpu/tlcs90/tlcs90.cpp

@@ -1022,6 +1022,7 @@ void tlcs90_device::decode()
 				if (b0 == 0xfe) {
 					OPCC( LDI+b1-0x58,14,18 )   NONE( 1 )       NONE( 2 )                   return;
 				}
+				[[fallthrough]]; // FIXME: really?
 
 				case 0x60:                                                                              // ADD A,g
 				case 0x61:                                                                              // ADC A,g
@@ -2776,6 +2777,7 @@ TIMER_CALLBACK_MEMBER( tlcs90_device::t90_timer_callback )
 	case 0x03: // 8bit PWM
 		logerror("CPU Timer %d expired with unhandled mode %d\n", i, mode);
 		// TODO: hmm...
+		[[fallthrough]]; // FIXME: really?
 	case 0x00: // 8bit
 		m_timer_value[i]++;
 		if ( m_timer_value[i] == m_treg_8bit[i] )

src/devices/cpu/tlcs90/tlcs90d.cpp

@@ -877,7 +877,7 @@ void tlcs90_disassembler::decode()
 				if (b0 == 0xfe) {
 					OPCC( LDI+b1-0x58,14,18 )   NONE( 1 )       NONE( 2 )                   return;
 				}
-
+				[[fallthrough]]; // FIXME: really?
 				case 0x60:                                                                              // ADD A,g
 				case 0x61:                                                                              // ADC A,g
 				case 0x62:                                                                              // SUB A,g

src/devices/cpu/tms7000/tms7000.cpp

@@ -585,6 +585,7 @@ void tms7000_device::tms7000_pf_w(offs_t offset, uint8_t data)
 					logerror("%s: CMOS low-power halt mode enabled\n", tag());
 			}
 			data &= ~0x20;
+			[[fallthrough]];
 		case 0x13:
 			// d0-d4: prescaler reload value
 			// d5: t2: cascade from t1

src/devices/cpu/z8/z8.cpp

@@ -702,7 +702,7 @@ void z8_device::t1_trigger()
 	case Z8_TMR_TIN_TRIGGER:
 		if (m_internal_timer[1]->enabled())
 			break;
-
+		[[fallthrough]];
 	case Z8_TMR_TIN_RETRIGGER:
 		if ((m_tmr & Z8_TMR_ENABLE_T1) != 0)
 		{

src/devices/machine/cdp1879.cpp

@@ -140,6 +140,7 @@ void cdp1879_device::write(offs_t offset, uint8_t data)
 				m_regs[offset + 6] = data;
 				break;
 			}
+			[[fallthrough]];
 		case R_CNT_DAYOFMONTH:
 		case R_CNT_MONTH:
 			m_regs[offset] = data;

src/devices/machine/ds1994.cpp

@@ -235,6 +235,7 @@ void ds1994_device::ds1994_rom_cmd(void)
 			case ROMCMD_SEARCHINT:
 				verboselog(0, "timer_main rom_command not implemented %02x\n", m_shift);
 				m_state[m_state_ptr] = STATE_COMMAND;
+				break;
 			default:
 				verboselog(0, "timer_main rom_command not found %02x\n", m_shift);
 				m_state[m_state_ptr] = STATE_IDLE;

src/devices/machine/fga002.cpp

@@ -682,7 +682,7 @@ void fga002_device::write(offs_t offset, uint8_t data){
 	case FGA_DMA_GENERAL    : LOG("FGA_DMA_GENERAL - not implemented\n"); m_fga002[FGA_DMA_GENERAL] = data; break;
 	case FGA_CTL12          : LOG("FGA_CTL12 - not implemented\n"); m_fga002[FGA_CTL12] = data; break;
 	case FGA_LIOTIMING      : LOG("FGA_LIOTIMING - not implemented\n"); m_fga002[FGA_LIOTIMING] = data; break;
-	case FGA_LOCALIACK      : do_fga002reg_localiack_w(data);
+	case FGA_LOCALIACK      : do_fga002reg_localiack_w(data); break;
 	case FGA_FMBCTL         : LOG("FGA_FMBCTL - not implemented\n"); m_fga002[FGA_FMBCTL] = data; break;
 	case FGA_FMBAREA        : LOG("FGA_FMBAREA - not implemented\n"); m_fga002[FGA_FMBAREA] = data; break;
 	case FGA_AUXSRCSTART    : LOG("FGA_AUXSRCSTART - not implemented\n"); m_fga002[FGA_AUXSRCSTART] = data; break;

src/devices/machine/i8271.cpp

@@ -754,12 +754,14 @@ void i8271_device::start_command(int cmd)
 	switch(cmd) {
 	case C_READ_DATA_SINGLE:
 		command[3] = 1;
+		[[fallthrough]];
 	case C_READ_DATA_MULTI:
 		read_data_start(flopi[BIT(command[0], 7)]);
 		break;
 
 	case C_VERIFY_DATA_SINGLE:
 		command[3] = 1;
+		[[fallthrough]];
 	case C_VERIFY_DATA_MULTI:
 		verify_data_start(flopi[BIT(command[0], 7)]);
 		break;
@@ -817,6 +819,7 @@ void i8271_device::start_command(int cmd)
 
 	case C_WRITE_DATA_SINGLE:
 		command[3] = 1;
+		[[fallthrough]];
 	case C_WRITE_DATA_MULTI:
 		write_data_start(flopi[BIT(command[0], 7)]);
 		break;

src/devices/machine/i8279.cpp

@@ -487,8 +487,9 @@ u8 i8279_device::data_r()
 				case 0x10: // underrun
 					if (!fifo_size)
 						break;
+					[[fallthrough]];
 				default:
-					printf("Invalid status: %X\n", m_status);
+					logerror("Invalid status: %X\n", m_status);
 			}
 		}
 		m_status = (m_status & 0xd0) | fifo_size; // turn off overrun & full

src/devices/machine/mb89374.cpp

@@ -326,6 +326,7 @@ void mb89374_device::write(offs_t offset, uint8_t data)
 
 		case REGISTER_RXIER:
 			m_rxier = data;
+			break;
 
 		case REGISTER_TXSR:
 			m_txsr = data | TXSR_MASK;

src/devices/machine/s3520cf.cpp

@@ -268,8 +268,8 @@ inline void s3520cf_device::rtc_write(u8 offset,u8 data)
 			case 0xa: m_rtc.month = (m_cntrl1 & 2) ? 1 : m_rtc.month + 0x10; check_overflow(); break;
 			case 0xb: m_rtc.year = (m_cntrl1 & 2) ? m_rtc.year & 0xf0 : m_rtc.year + 1; check_overflow(); break;
 			case 0xc: m_rtc.year = (m_cntrl1 & 2) ? m_rtc.year & 0x0f : m_rtc.year + 0x10; check_overflow(); break;
-			case 0xd: m_cntrl1 = data & 0xf;
+			case 0xd: m_cntrl1 = data & 0xf; break;
-			case 0xe: m_cntrl2 = data & 0xf;
+			case 0xe: m_cntrl2 = data & 0xf; break;
 			}
 	}
 }

src/devices/machine/strata.cpp

@@ -500,6 +500,7 @@ void strataflash_device::write8_16(offs_t offset, uint16_t data, bus_width_t bus
 		else
 			m_wrbuf_base = offset;
 		memset(m_wrbuf, 0xff, m_wrbuf_len); /* right??? */
+		[[fallthrough]];
 	case FM_WRBUFPART3:
 		if ((offset < m_wrbuf_base) || (offset >= (m_wrbuf_base + m_wrbuf_len)))
 			m_status |= 0x30;

src/devices/machine/vrc5074.cpp

@@ -883,6 +883,7 @@ void vrc5074_device::cpu_reg_w(offs_t offset, uint32_t data, uint32_t mem_mask)
 	case NREG_CPUSTAT + 0:    /* CPU status */
 		if (data & 0x1) logerror("cpu_reg_w: System Cold Reset\n");
 		if (data & 0x2) logerror("cpu_reg_w: CPU Warm Reset\n");
+		[[fallthrough]];
 	case NREG_CPUSTAT + 1:    /* CPU status */
 		if (LOG_NILE) logerror("%s NILE WRITE: CPU status(%03X) = %08X & %08X\n", machine().describe_context(), offset * 4, data, mem_mask);
 		logit = 0;

src/devices/sound/namco.cpp

@@ -522,6 +522,7 @@ void namco_15xx_device::namco_15xx_w(offs_t offset, uint8_t data)
 
 	case 0x06:
 		voice->waveform_select = (data >> 4) & 7;
+		[[fallthrough]];
 	case 0x04:
 	case 0x05:
 		/* the frequency has 20 bits */
@@ -598,6 +599,7 @@ void namco_cus30_device::namcos1_sound_w(offs_t offset, uint8_t data)
 
 	case 0x01:
 		voice->waveform_select = (data >> 4) & 15;
+		[[fallthrough]];
 	case 0x02:
 	case 0x03:
 		/* the frequency has 20 bits */

src/devices/sound/tms5220.cpp

@@ -1770,6 +1770,7 @@ void tms5220_device::device_timer(emu_timer &timer, device_timer_id id, int para
 			case 0x03:
 				/* High Impedance */
 				m_io_ready = param;
+				break;
 			case 0x00:
 				/* illegal */
 				m_io_ready = param;

src/devices/video/mos6566.cpp

@@ -1152,6 +1152,8 @@ void mos6566_device::execute_run()
 			// Third sample of border state
 			m_border_on_sample[2] = m_border_on;
 
+			[[fallthrough]]; // FIXME: really?
+
 		// Graphics
 
 		case 19:
@@ -1739,6 +1741,8 @@ void mos6569_device::execute_run()
 			// Third sample of border state
 			m_border_on_sample[2] = m_border_on;
 
+			[[fallthrough]]; // FIXME: really?
+
 		// Graphics
 
 		case 19:

src/devices/video/pc_vga.cpp

@@ -2444,6 +2444,7 @@ uint8_t tseng_vga_device::port_03c0_r(offs_t offset)
 			break;
 		case 0x08:
 			et4k.dac_state = 0;
+			[[fallthrough]];
 		default:
 			res = vga_device::port_03c0_r(offset);
 			break;
@@ -2481,6 +2482,7 @@ void tseng_vga_device::port_03c0_w(offs_t offset, uint8_t data)
 				et4k.dac_ctrl = data;
 				break;
 			}
+			[[fallthrough]];
 		default:
 			vga_device::port_03c0_w(offset,data);
 			break;
@@ -4434,6 +4436,7 @@ bit   0-2  (911-928) READ-REG-SEL. Read Register Select. Selects the register
 	case 0xf000:
 		ibm8514.multifunc_sel = data & 0x000f;
 		if(LOG_8514) logerror("S3: Multifunction select write %04x\n",data);
+		break;
 	default:
 		if(LOG_8514) logerror("S3: Unimplemented multifunction register %i write %03x\n",data >> 12,data & 0x0fff);
 	}

src/devices/video/voodoo.cpp

@@ -1630,7 +1630,7 @@ void voodoo_device::recompute_video_memory()
 	{
 		case 3: /* reserved */
 			logerror("VOODOO.ERROR:Unexpected memory configuration in recompute_video_memory!\n");
-
+			[[fallthrough]];
 		case 0: /* 2 color buffers, 1 aux buffer */
 			fbi.rgboffs[2] = ~0;
 			fbi.auxoffs = 2 * buffer_pages * 0x1000;
@@ -4591,6 +4591,7 @@ uint32_t voodoo_device::register_r(voodoo_device *vd, offs_t offset)
 		case fbiAfuncFail:
 		case fbiPixelsOut:
 			vd->update_statistics(true);
+			[[fallthrough]];
 		case fbiTrianglesOut:
 			result = vd->reg[regnum].u & 0xffffff;
 			break;

src/devices/video/zeus2.cpp

@@ -1222,7 +1222,7 @@ bool zeus2_device::zeus2_fifo_process(const uint32_t *data, int numwords)
 				return false;
 			zeus_trans[3] = convert_float(data[1]);
 			dataoffs = 1;
-
+			[[fallthrough]];
 		/* 0x07: set matrix and point (crusnexo) */
 		case 0x07:
 			if (numwords < 13)
@@ -1294,6 +1294,7 @@ bool zeus2_device::zeus2_fifo_process(const uint32_t *data, int numwords)
 				}
 				break;
 			}
+			[[fallthrough]];
 		// 0x1b: thegrid
 		// 0x1c: crusnexo (4 words)
 		case 0x1b:
@@ -1471,6 +1472,7 @@ void zeus2_device::zeus2_draw_model(uint32_t baseaddr, uint16_t count, int logit
 					case 0x00: // crusnexo
 						if (logit && curoffs == count)
 							logerror(" end cmd 00\n");
+						[[fallthrough]];
 					case 0x21:  /* thegrid */
 					case 0x22:  /* crusnexo */
 						// Sets 0x68 (uv float offset) and texture line and mode

src/frontend/mame/luaengine.cpp

@@ -88,18 +88,24 @@ namespace sol
 	};
 	template<>
 	struct is_container<core_options> : std::false_type {}; // don't convert core_optons to a table directly
-	namespace stack
+	sol::buffer *sol_lua_get(sol::types<buffer *>, lua_State *L, int index, sol::stack::record &tracking)
 	{
-		template <>
+		return new sol::buffer(stack::get<int>(L, index), L);
-		struct pusher<osd_file::error>
+	}
-		{
+	int sol_lua_push(sol::types<buffer *>, lua_State *L, buffer *value)
-			static int push(lua_State *L, osd_file::error error)
 	{
+		delete value;
+		return 1;
+	}
+}
+
+int sol_lua_push(sol::types<osd_file::error>, lua_State *L, osd_file::error &&value)
+{
 	const char *strerror;
-				switch(error)
+	switch(value)
 	{
 		case osd_file::error::NONE:
-						return stack::push(L, sol::nil);
+			return sol::stack::push(L, sol::nil);
 		case osd_file::error::FAILURE:
 			strerror = "failure";
 			break;
@@ -128,42 +134,19 @@ namespace sol
 			strerror = "unknown_error";
 			break;
 	}
-				return stack::push(L, strerror);
+	return sol::stack::push(L, strerror);
-			}
+}
-		};
+
-		template <>
+template <typename Handler>
-		struct checker<sol::buffer *>
+bool sol_lua_check(sol::types<osd_file::error>, lua_State *L, int index, Handler &&handler, sol::stack::record &tracking)
-		{
+{
-			template <typename Handler>
+	return sol::stack::check<int>(L, index, std::forward<Handler>(handler));
-			static bool check (lua_State* L, int index, Handler&& handler, record& tracking)
+}
-			{
+
-				return stack::check<int>(L, index, handler);
+int sol_lua_push(sol::types<map_handler_type>, lua_State *L, map_handler_type &&value)
-			}
+{
-		};
-		template <>
-		struct getter<sol::buffer *>
-		{
-			static sol::buffer *get(lua_State* L, int index, record& tracking)
-			{
-				return new sol::buffer(stack::get<int>(L, index), L);
-			}
-		};
-		template <>
-		struct pusher<sol::buffer *>
-		{
-			static int push(lua_State* L, sol::buffer *buff)
-			{
-				delete buff;
-				return 1;
-			}
-		};
-		template <>
-		struct pusher<map_handler_type>
-		{
-			static int push(lua_State *L, map_handler_type type)
-			{
 	const char *typestr;
-				switch(type)
+	switch(value)
 	{
 		case AMH_NONE:
 			typestr = "none";
@@ -201,13 +184,9 @@ namespace sol
 			typestr = "unknown";
 			break;
 	}
-				return stack::push(L, typestr);
+	return sol::stack::push(L, typestr);
-			}
-		};
-	}
 }
 
-
 namespace
 {
 	// ======================> enum_parser
@@ -1966,7 +1945,7 @@ void lua_engine::initialize()
 			return port_table;
 		}));
 	ioport_manager_type.set("type_seq", [](ioport_manager &m, ioport_type type, int player, input_seq_type seqtype) {
-			return sol::make_user(m.type_seq(type, player, seqtype));
+			return sol::make_user(input_seq(m.type_seq(type, player, seqtype)));
 		});
 	sol().registry().set("ioport", ioport_manager_type);
 
@@ -2080,7 +2059,7 @@ void lua_engine::initialize()
 
 	auto ioport_field_type = sol().registry().new_usertype<ioport_field>("new", sol::no_constructor);
 	ioport_field_type.set("set_value", &ioport_field::set_value);
-	ioport_field_type.set("set_input_seq", [](ioport_field &f, const std::string &seq_type_string, sol::user<input_seq> seq) {
+	ioport_field_type.set("set_input_seq", [](ioport_field &f, const std::string &seq_type_string, const input_seq &seq) {
 			input_seq_type seq_type = s_seq_type_parser(seq_type_string);
 			ioport_field::user_settings settings;
 			f.get_user_settings(settings);
@@ -2089,15 +2068,15 @@ void lua_engine::initialize()
 		});
 	ioport_field_type.set("input_seq", [](ioport_field &f, const std::string &seq_type_string) {
 			input_seq_type seq_type = s_seq_type_parser(seq_type_string);
-			return sol::make_user(f.seq(seq_type));
+			return sol::make_user(input_seq(f.seq(seq_type)));
 		});
-	ioport_field_type.set("set_default_input_seq", [](ioport_field &f, const std::string &seq_type_string, sol::user<input_seq> seq) {
+	ioport_field_type.set("set_default_input_seq", [](ioport_field &f, const std::string &seq_type_string, const input_seq &seq) {
 			input_seq_type seq_type = s_seq_type_parser(seq_type_string);
 			f.set_defseq(seq_type, seq);
 		});
 	ioport_field_type.set("default_input_seq", [](ioport_field &f, const std::string &seq_type_string) {
 			input_seq_type seq_type = s_seq_type_parser(seq_type_string);
-			return sol::make_user(f.defseq(seq_type));
+			return sol::make_user(input_seq(f.defseq(seq_type)));
 		});
 	ioport_field_type.set("keyboard_codes", [this](ioport_field &f, int which) {
 			sol::table result = sol().create_table();
@@ -2316,14 +2295,14 @@ void lua_engine::initialize()
 
 	auto input_type = sol().registry().new_usertype<input_manager>("new", sol::no_constructor);
 	input_type.set("code_from_token", [](input_manager &input, const char *token) { return sol::make_user(input.code_from_token(token)); });
-	input_type.set("code_pressed", [](input_manager &input, sol::user<input_code> code) { return input.code_pressed(code); });
+	input_type.set("code_pressed", [](input_manager &input, const input_code &code) { return input.code_pressed(code); });
-	input_type.set("code_to_token", [](input_manager &input, sol::user<input_code> code) { return input.code_to_token(code); });
+	input_type.set("code_to_token", [](input_manager &input, const input_code &code) { return input.code_to_token(code); });
-	input_type.set("code_name", [](input_manager &input, sol::user<input_code> code) { return input.code_name(code); });
+	input_type.set("code_name", [](input_manager &input, const input_code &code) { return input.code_name(code); });
-	input_type.set("seq_from_tokens", [](input_manager &input, const char *tokens) { input_seq seq; input.seq_from_tokens(seq, tokens); return sol::make_user(seq); });
+	input_type.set("seq_from_tokens", [](input_manager &input, const char *tokens) { input_seq seq; input.seq_from_tokens(seq, tokens); return sol::make_user(std::move(seq)); });
-	input_type.set("seq_pressed", [](input_manager &input, sol::user<input_seq> seq) { return input.seq_pressed(seq); });
+	input_type.set("seq_pressed", [](input_manager &input, const input_seq &seq) { return input.seq_pressed(seq); });
-	input_type.set("seq_to_tokens", [](input_manager &input, sol::user<input_seq> seq) { return input.seq_to_tokens(seq); });
+	input_type.set("seq_to_tokens", [](input_manager &input, const input_seq &seq) { return input.seq_to_tokens(seq); });
-	input_type.set("seq_name", [](input_manager &input, sol::user<input_seq> seq) { return input.seq_name(seq); });
+	input_type.set("seq_name", [](input_manager &input, const input_seq &seq) { return input.seq_name(seq); });
-	input_type.set("seq_clean", [](input_manager &input, sol::user<input_seq> seq) { input_seq cleaned_seq = input.seq_clean(seq); return sol::make_user(cleaned_seq); });
+	input_type.set("seq_clean", [](input_manager &input, const input_seq &seq) { return sol::make_user(input.seq_clean(seq)); });
 	input_type.set("seq_poll_start", [this](input_manager &input, const char *cls_string, sol::object seq) {
 			if (!m_seq_poll)
 				m_seq_poll.reset(new input_sequence_poller(input));
@@ -2353,7 +2332,7 @@ void lua_engine::initialize()
 	input_type.set("seq_poll_final", [this](input_manager &input) -> sol::object {
 			if (!m_seq_poll)
 				return sol::make_object(sol(), sol::nil);
-			return sol::make_object(sol(), sol::make_user(m_seq_poll->valid() ? m_seq_poll->sequence() : input_seq()));
+			return sol::make_object(sol(), sol::make_user(m_seq_poll->valid() ? input_seq(m_seq_poll->sequence()) : input_seq()));
 		});
 	input_type.set("seq_poll_modified", [this](input_manager &input) -> sol::object {
 			if (!m_seq_poll)
@@ -2368,7 +2347,7 @@ void lua_engine::initialize()
 	input_type.set("seq_poll_sequence", [this](input_manager &input) -> sol::object {
 			if (!m_seq_poll)
 				return sol::make_object(sol(), sol::nil);
-			return sol::make_object(sol(), sol::make_user(m_seq_poll->sequence()));
+			return sol::make_object(sol(), sol::make_user(input_seq(m_seq_poll->sequence())));
 	});
 	input_type.set("device_classes", sol::property([this](input_manager &input) {
 			sol::table result = sol().create_table();
@@ -2449,7 +2428,7 @@ void lua_engine::initialize()
 	input_device_item_type.set("token", sol::property(&input_device_item::token));
 	input_device_item_type.set("code", [](input_device_item &item) {
 			input_code code(item.device().devclass(), item.device().devindex(), item.itemclass(), ITEM_MODIFIER_NONE, item.itemid());
-			return sol::make_user(code);
+			return sol::make_user(std::move(code));
 		});
 	sol().registry().set("input_device_item", input_device_item_type);
 
@@ -2974,7 +2953,8 @@ void lua_engine::initialize()
 	image_type.set("create", [](device_image_interface &di, const std::string &filename) { return di.create(filename); });
 	image_type.set("crc", &device_image_interface::crc);
 	image_type.set("display", [](device_image_interface &di) { return di.call_display(); });
-	image_type.set("device", sol::property(static_cast<const device_t &(device_image_interface::*)() const>(&device_image_interface::device)));
+	// FIXME: the next line is causing sol3 to try instantiating device_t for some reason
+	//image_type.set("device", sol::property(static_cast<const device_t & (device_image_interface::*)() const>(&device_image_interface::device));
 	image_type.set("instance_name", sol::property(&device_image_interface::instance_name));
 	image_type.set("brief_instance_name", sol::property(&device_image_interface::brief_instance_name));
 	image_type.set("is_readable", sol::property(&device_image_interface::is_readable));

src/lib/formats/cqm_dsk.cpp

@@ -308,6 +308,7 @@ bool cqm_format::load(io_generic *io, uint32_t form_factor, floppy_image *image)
 			if (heads == 1)
 				return false; // single side ED ?
 			image->set_variant(floppy_image::DSED);
+			[[fallthrough]]; // FIXME: really?
 		default:
 			return false;
 	}

src/mame/audio/vboy.cpp

@@ -442,6 +442,7 @@ void vboysnd_device::write(offs_t offset, uint8_t data)
 					break;
 				}
 			}
+			[[fallthrough]]; // FIXME: really?
 		case SxINT:
 			if (channel < 5)
 			{

src/mame/drivers/altos8600.cpp

@@ -323,6 +323,7 @@ void altos8600_state::hd_w(offs_t offset, u8 data)
 						m_stat |= 0xa;
 						break;
 					}
+					[[fallthrough]];
 				case 0x4:
 					m_secoff = 0;
 					m_stat |= 1;

src/mame/drivers/barata.cpp

@@ -213,6 +213,7 @@ void barata_state::fpga_send(unsigned char cmd)
 				{
 					m_lamps[lamp_index] = state ? 0 : 1;
 				}
+				[[fallthrough]]; // FIXME: really?
 			default:
 				mode = FPGA_WAITING_FOR_NEW_CMD;
 				break;
@@ -248,6 +249,7 @@ void barata_state::fpga_send(unsigned char cmd)
 					m_digits[2*counter_bank] = dec_7seg(counter_data/10);
 					m_digits[2*counter_bank+1] = dec_7seg(counter_data%10);
 				}
+				[[fallthrough]]; // FIXME: really?
 			default:
 				mode = FPGA_WAITING_FOR_NEW_CMD;
 				break;
@@ -265,6 +267,7 @@ void barata_state::fpga_send(unsigned char cmd)
 			case 2:
 				sample_index = (sample_index << 3) | cmd;
 				logerror("PLAY_SAMPLE #%d.\n", sample_index);
+				[[fallthrough]]; // FIXME: really?
 			default:
 				mode = FPGA_WAITING_FOR_NEW_CMD;
 				break;

src/mame/drivers/besta.cpp

@@ -70,6 +70,7 @@ void besta_state::mpcc_reg_w(offs_t offset, uint8_t data)
 			break;
 		case 10:
 			m_terminal->write(data);
+			[[fallthrough]]; // FIXME: really?
 		default:
 			m_mpcc_regs[offset] = data;
 			break;

src/mame/drivers/bfm_swp.cpp

@@ -145,15 +145,15 @@ uint32_t bfm_swp_state::bfm_swp_mem_r(offs_t offset, uint32_t mem_mask)
 	switch ( cs )
 	{
 		case 1:
-			if (offset<0x100000/4) return m_cpuregion[offset];
+			if (offset<0x100000/4)
-
+				return m_cpuregion[offset];
+			[[fallthrough]]; // FIXME: really?
 		case 2:
 			offset&=0x3fff;
 			return m_mainram[offset];
 
 		default:
 			logerror("%08x maincpu read access offset %08x mem_mask %08x cs %d\n", pc, offset*4, mem_mask, cs);
-
 	}
 
 	return 0x0000;

src/mame/drivers/cops.cpp

@@ -430,7 +430,6 @@ void cops_state::dacia_w(offs_t offset, uint8_t data)
 	switch(offset & 0x07)
 	{
 		case 0: /* IRQ enable Register 1 */
-		{
 			m_dacia_irq1_reg &= ~0x80;
 
 			if (data & 0x80) //enable bits
@@ -444,10 +443,8 @@ void cops_state::dacia_w(offs_t offset, uint8_t data)
 			if (LOG_DACIA) logerror("DACIA IRQ 1 Register: %02x\n", m_dacia_irq1_reg);
 			update_dacia_irq();
 			break;
-		}
 
 		case 1: /* Control / Format Register 1 */
-		{
 			if (data & 0x80) //Format Register
 			{
 				m_dacia_rts1 = (data & 0x01);
@@ -478,13 +475,12 @@ void cops_state::dacia_w(offs_t offset, uint8_t data)
 
 			}
 			break;
-		}
+
 		case 2: /* Compare / Aux Ctrl Register 1 */
-		{
 			if (m_dacia_reg1 == CMP_REGISTER)
 			{
-				m_dacia_cmp1 =1;
+				m_dacia_cmp1 = 1;
-				m_dacia_cmpval1=data;
+				m_dacia_cmpval1 = data;
 				if (LOG_DACIA) logerror("DACIA Compare mode: %02x \n", data);
 //              update_dacia_irq();
 			}
@@ -492,15 +488,13 @@ void cops_state::dacia_w(offs_t offset, uint8_t data)
 			{
 				if (LOG_DACIA) logerror("DACIA Aux ctrl: %02x \n", data);
 			}
-		}
+			[[fallthrough]]; // FIXME: really?
 		case 3: /* Transmit Data Register 1 */
-		{
 			if (LOG_DACIA) logerror("DACIA Transmit: %02x %c\n", data, (char)data);
 			m_ld->command_w(data);
 			break;
-		}
+
 		case 4: /* IRQ enable Register 2 */
-		{
 			m_dacia_irq2_reg &= ~0x80;
 
 			if (data & 0x80) //enable bits
@@ -514,10 +508,8 @@ void cops_state::dacia_w(offs_t offset, uint8_t data)
 			if (LOG_DACIA) logerror("DACIA IRQ 2 Register: %02x\n", m_dacia_irq2_reg);
 			update_dacia_irq();
 			break;
-		}
 
 		case 5: /* Control / Format Register 2 */
-		{
 			if (data & 0x80) //Format Register
 			{
 				m_dacia_rts2 = (data & 0x01);
@@ -548,9 +540,8 @@ void cops_state::dacia_w(offs_t offset, uint8_t data)
 
 			}
 			break;
-		}
+
 		case 6: /* Compare / Aux Ctrl Register 2 */
-		{
 			if (m_dacia_reg2 == CMP_REGISTER)
 			{
 				m_dacia_cmp2 =1;
@@ -562,9 +553,8 @@ void cops_state::dacia_w(offs_t offset, uint8_t data)
 			{
 				if (LOG_DACIA) logerror("DACIA Aux ctrl 2: %02x \n", data);
 			}
-		}
+			[[fallthrough]]; // FIXME: really?
 		case 7: /* Transmit Data Register 2 */
-		{
 			if (LOG_DACIA) logerror("DACIA Transmit 2: %02x %c\n", data, (char)data);
 
 		//  for (int i=0; i <8; i++)
@@ -574,7 +564,6 @@ void cops_state::dacia_w(offs_t offset, uint8_t data)
 //          m_ld->command_w(data);
 			break;
 	}
-	}
 }
 /*************************************
  *

src/mame/drivers/cosmic.cpp

@@ -280,6 +280,7 @@ void cosmic_state::cosmica_sound_output_w(offs_t offset, uint8_t data)
 					break;
 				}
 			}
+			[[fallthrough]]; // FIXME: really?
 
 		case 3: /*Dive Bombing Type B (G.S.B)*/
 			if (data)

src/mame/drivers/cxhumax.cpp

@@ -427,6 +427,7 @@ void cxhumax_state::cx_uart2_w(offs_t offset, uint32_t data, uint32_t mem_mask)
 					}
 				}
 			}
+			[[fallthrough]];
 		default:
 			COMBINE_DATA(&m_uart2_regs[offset]); break;
 	}

src/mame/drivers/fcrash.cpp

@@ -255,6 +255,7 @@ void fcrash_state::sf2m1_layer_w(offs_t offset, uint16_t data)
 			data = 0x0b4e;
 			break;
 		}
+		[[fallthrough]];
 	case 0xb3:
 		m_cps_b_regs[m_layer_enable_reg / 2] = data;
 		break;

src/mame/drivers/model3.cpp

@@ -790,6 +790,7 @@ uint32_t model3_state::pci_device_get_reg()
 					logerror("pci_device_get_reg: Device 11, unknown reg %02X", reg);
 					break;
 			}
+			[[fallthrough]]; // FIXME: really?
 
 		case 13:        /* Real3D Controller chip */
 			switch(reg)

src/mame/drivers/mpu4vid.cpp

@@ -1997,9 +1997,14 @@ void mpu4vid_state::mpu4_vid_bt_a00002_w(offs_t offset, uint8_t data)
 {
 	switch (m_bt_which)
 	{
-	case 0: m_btpal_r[m_bt_palbase] = data;
+	case 0:
-	case 1: m_btpal_g[m_bt_palbase] = data;
+		m_btpal_r[m_bt_palbase] = data;
-	case 2: m_btpal_b[m_bt_palbase] = data;
+		[[fallthrough]]; // FIXME: really?
+	case 1:
+		m_btpal_g[m_bt_palbase] = data;
+		[[fallthrough]]; // FIXME: really?
+	case 2:
+		m_btpal_b[m_bt_palbase] = data;
 	}
 
 	m_bt_which++;

src/mame/drivers/mpu5.cpp

@@ -275,12 +275,11 @@ void mpu5_state::asic_w8(offs_t offset, uint8_t data)
 			break;
 
 		case 0x09:
-		{
 			//Assume SEC fitted for now
 			m_sec->data_w(~data&0x01);
 			m_sec->clk_w(~data&0x02);
 			m_sec->cs_w(~data&0x04);
-		}
+			[[fallthrough]];
 		case 0x0b:
 			output().set_value("statuslamp1", BIT(data, 4));
 			output().set_value("statuslamp2", BIT(data, 5));

src/mame/drivers/psion5.cpp

@@ -652,6 +652,7 @@ void psion5mx_state::periphs_w(offs_t offset, uint32_t data, uint32_t mem_mask)
 		case REG_PADR:
 			LOGMASKED(LOG_GPIO_WRITES, "%s: peripheral write, PADR = %08x & %08x\n", machine().describe_context(), data, mem_mask);
 			m_ports[PORTA] = data;
+			break;
 		case REG_PBDR:
 		{
 			LOGMASKED(LOG_GPIO_WRITES, "%s: peripheral write, PBDR = %08x & %08x\n", machine().describe_context(), data, mem_mask);

src/mame/drivers/rainbow.cpp

@@ -1601,7 +1601,7 @@ uint8_t rainbow_modelb_state::rtc_r(offs_t offset)
 		case 0x2004:  // 0xFE004 (MIRROR)
 			if (m_rtc->chip_enable())
 				return (m_rtc->read_data() & 0x01);
-
+			[[fallthrough]]; // FIXME: really?
 		// (RTC ACTIVATION) read magic pattern 0
 		case 0x0100:  // 0xFC100
 		case 0x2100:  // 0xFE100 (MIRROR)

src/mame/drivers/ti89.cpp

@@ -79,6 +79,7 @@ void ti68k_state::ti68k_io_w(offs_t offset, uint16_t data)
 			break;
 		case 0x0b:
 			m_timer_val = data & 0xff;
+			[[fallthrough]]; // FIXME: really?
 		case 0x0c:
 			m_kb_mask = data & 0x03ff;
 			break;

src/mame/drivers/tx0.cpp

@@ -899,7 +899,7 @@ void tx0_state::magtape_callback()
 	{
 	case MTS_UNSELECTING:
 		m_magtape.state = MTS_UNSELECTED;
-
+		[[fallthrough]];
 	case MTS_UNSELECTED:
 		if (m_magtape.sel_pending)
 		{
@@ -960,7 +960,7 @@ void tx0_state::magtape_callback()
 			}
 			break;
 		}
-
+		[[fallthrough]];
 	case MTS_SELECTED:
 		switch (m_magtape.command)
 		{
@@ -1254,7 +1254,7 @@ void tx0_state::magtape_callback()
 				{
 					m_magtape.u.write.state = MTWTS_STATE1;
 				}
-
+				[[fallthrough]];
 			case MTWTS_STATE1:
 				if (m_magtape.u.write.counter)
 				{
@@ -1282,7 +1282,7 @@ void tx0_state::magtape_callback()
 						m_magtape.u.write.counter = 3;
 					}
 				}
-
+				[[fallthrough]];
 			case MTWTS_STATE2:
 				if (m_magtape.u.write.counter != 0)
 				{

src/mame/machine/3do.cpp

@@ -637,6 +637,7 @@ void _3do_state::madam_w(offs_t offset, uint32_t data, uint32_t mem_mask){
 	case 0x0680/4: case 0x0684/4: case 0x0688/4: case 0x068c/4:
 	case 0x0690/4: case 0x0694/4: case 0x0698/4: case 0x069c/4:
 		m_madam.mult[offset & 0x3f] = data;
+		[[fallthrough]];
 	case 0x07f0/4:
 		m_madam.mult_control |= data;
 		break;

src/mame/machine/amiga.cpp

@@ -1176,11 +1176,11 @@ uint16_t amiga_state::custom_chip_r(offs_t offset)
 		case REG_JOY0DAT:
 			if (m_joy0dat_port.found())
 				return joy0dat_r();
-
+			[[fallthrough]]; // FIXME: Really?  Fall through to potentially reading the other joystick?
 		case REG_JOY1DAT:
 			if (m_joy1dat_port.found())
 				return joy1dat_r();
-
+			[[fallthrough]]; // TODO: check that this is correct
 		case REG_POTGOR:
 			return m_potgo_port.read_safe(0x5500);
 

src/mame/machine/arkanoid.cpp

@@ -383,6 +383,7 @@ void arkanoid_state::arkanoid_bootleg_d018_w(uint8_t data)
 						m_bootleg_cmd = 0x00;
 					if (m_maincpu->pc() == 0x7c47)
 						m_bootleg_cmd = 0x00;
+					[[fallthrough]]; // FIXME: really?
 				case 0x89:  /* unneeded value : no read back */
 					if (m_maincpu->pc() == 0x67e5)
 						m_bootleg_cmd = 0x00;
@@ -433,6 +434,7 @@ void arkanoid_state::arkanoid_bootleg_d018_w(uint8_t data)
 						m_bootleg_cmd = 0x00;
 					if (m_maincpu->pc() == 0x7c47)
 						m_bootleg_cmd = 0x00;
+					[[fallthrough]]; // FIXME: really?
 				case 0x89:  /* unneeded value : no read back */
 					if (m_maincpu->pc() == 0x67e5)
 						m_bootleg_cmd = 0x00;

src/mame/machine/isbc_215g.cpp

@@ -192,6 +192,7 @@ void isbc_215g_device::io_w(offs_t offset, uint16_t data)
 				find_sector();
 			else if(m_amsrch)
 				logerror("isbc_215g: address search without read gate\n");
+			[[fallthrough]];
 		case 0x01:
 			m_stepdir = (data & 0x80) ? 1 : 0;
 			break;

src/mame/machine/lynx.cpp

@@ -1111,14 +1111,18 @@ void lynx_state::suzy_write(offs_t offset, uint8_t data)
 			break;
 		case HPOSSTRTL:
 			m_blitter.x_pos = data;
+			[[fallthrough]]; // FIXME: really?
 		case HPOSSTRTH:
 			m_blitter.x_pos &= 0xff;
 			m_blitter.x_pos |= data<<8;
+			[[fallthrough]]; // FIXME: really?
 		case VPOSSTRTL:
 			m_blitter.y_pos = data;
+			[[fallthrough]]; // FIXME: really?
 		case VPOSSTRTH:
 			m_blitter.y_pos &= 0xff;
 			m_blitter.y_pos |= data<<8;
+			[[fallthrough]]; // FIXME: really?
 		case SPRHSIZL:
 			m_blitter.width = data;
 			break;

src/mame/machine/mpu4.cpp

@@ -963,6 +963,7 @@ void mpu4_state::pia_ic5_porta_w(uint8_t data)
 					m_aux1_input|= 0xd0;
 					break;
 				}
+				break;
 
 			case 0x01: //Middle row - note switches don't match pattern
 				switch (machine().rand() & 0x3)
@@ -987,6 +988,7 @@ void mpu4_state::pia_ic5_porta_w(uint8_t data)
 					m_aux1_input|= 0x90;
 					break;
 				}
+				break;
 
 			case 0x02: //Bottom row
 				switch (machine().rand() & 0x3)
@@ -1011,6 +1013,7 @@ void mpu4_state::pia_ic5_porta_w(uint8_t data)
 					m_aux1_input|= 0x30;
 					break;
 				}
+				break;
 			}
 		}
 	}

src/mame/machine/n64.cpp

@@ -1754,6 +1754,7 @@ int n64_periphs::pif_channel_handle_command(int channel, int slength, uint8_t *s
 							rdata[2] = 0x01;
 							return 0;
 					}
+					[[fallthrough]]; // FIXME: really?
 				}
 				case 4:
 				{

src/mame/machine/twincobr.cpp

@@ -75,6 +75,7 @@ void twincobr_state::twincobr_dsp_w(u16 data)
 	switch (m_main_ram_seg)
 	{
 	case 0x30000:   if ((m_dsp_addr_w < 3) && (data == 0)) m_dsp_execute = 1;
+		[[fallthrough]];
 	case 0x40000:
 	case 0x50000:  {address_space &mainspace = m_maincpu->space(AS_PROGRAM);
 					mainspace.write_word(m_main_ram_seg + m_dsp_addr_w, data);
@@ -125,6 +126,7 @@ void twincobr_state::wardner_dsp_w(u16 data)
 	switch (m_main_ram_seg)
 	{
 	case 0x7000:    if ((m_dsp_addr_w < 3) && (data == 0)) m_dsp_execute = 1;
+		[[fallthrough]];
 	case 0x8000:
 	case 0xa000:   {address_space &mainspace = m_maincpu->space(AS_PROGRAM);
 					mainspace.write_byte(m_main_ram_seg + (m_dsp_addr_w + 0), (data & 0xff));

src/mame/video/dynax.cpp

@@ -946,6 +946,7 @@ uint32_t dynax_state::screen_update_hanamai(screen_device &screen, bitmap_ind16
 	switch (m_hanamai_priority)
 	{
 		default:    popmessage("unknown priority %02x", m_hanamai_priority);
+		[[fallthrough]]; // FIXME: really?
 		case 0x10:  lay[0] = 0; lay[1] = 1; lay[2] = 2; lay[3] = 3; break;
 		case 0x11:  lay[0] = 0; lay[1] = 3; lay[2] = 2; lay[3] = 1; break;
 		case 0x12:  lay[0] = 0; lay[1] = 1; lay[2] = 3; lay[3] = 2; break;

src/mame/video/k007342.cpp

@@ -153,6 +153,7 @@ void k007342_device::vreg_w(offs_t offset, uint8_t data)
 		case 0x01:  /* used for banking in Rock'n'Rage */
 			if (data != m_regs[1])
 				machine().tilemap().mark_all_dirty();
+			[[fallthrough]];
 		case 0x02:
 			m_scrollx[0] = (m_scrollx[0] & 0xff) | ((data & 0x01) << 8);
 			m_scrollx[1] = (m_scrollx[1] & 0xff) | ((data & 0x02) << 7);

src/mame/video/konamigx.cpp

@@ -587,6 +587,7 @@ void konamigx_state::konamigx_mixer(screen_device &screen, bitmap_rgb32 &bitmap,
 			// Daisukiss bad shadow filter
 			case  4:
 				if (k & 0x3000 || k == 0x0800) continue;
+				[[fallthrough]];
 
 			// Tokkae shadow masking (INACCURATE)
 			case  5:

src/mame/video/psychic5.cpp

@@ -310,6 +310,7 @@ void psychic5_state::draw_background(screen_device &screen, bitmap_rgb32 &bitmap
 		case  3: case  7: if (m_sy2 == 0xf0) m_bg_clip_mode++; break;
 		case  9: case 11: if (m_sx1 == 0xf0) m_bg_clip_mode++; break;
 		case 13: case 15: if (sx1_old == 0xf0) m_bg_clip_mode++;
+			[[fallthrough]];
 		case 16: if (m_sy1 != 0x00) m_bg_clip_mode = 0; break;
 		}
 

src/mame/video/vc4000.cpp

@@ -426,7 +426,7 @@ void vc4000_state::vc4000_sprite_update(bitmap_ind16 &bitmap, uint8_t *collision
 	case 0:
 		if (m_video.line != This->y + 2) break;
 		This->state++;
-
+		[[fallthrough]];
 	case 1: case 2: case 3: case 4: case 5: case 6: case 7: case 8:case 9:case 10:
 
 		vc4000_collision_plot(collision+This->data->x1, This->data->bitmap[This->state-1],This->mask,This->size);
@@ -471,7 +471,7 @@ void vc4000_state::vc4000_sprite_update(bitmap_ind16 &bitmap, uint8_t *collision
 
 		This->delay=0;
 		This->state++;
-
+		[[fallthrough]];
 	case 12:
 		if (This->y!=0)
 		{
@@ -479,7 +479,7 @@ void vc4000_state::vc4000_sprite_update(bitmap_ind16 &bitmap, uint8_t *collision
 			break;
 		}
 		This->state++;
-
+		[[fallthrough]];
 	case 13: case 14: case 15: case 16: case 17: case 18: case 19:case 20:case 21:case 22:
 
 		vc4000_collision_plot(collision+This->data->x2,This->data->bitmap[This->state-13],This->mask,This->size);

src/osd/modules/render/d3d/d3dhlsl.cpp

@@ -2599,6 +2599,7 @@ void uniform::update()
 			break;
 		case CU_CHROMA_CONVERSION_GAIN:
 			m_shader->set_vector("ConversionGain", 3, &options->chroma_conversion_gain[0]);
+			break;
 		case CU_CHROMA_Y_GAIN:
 			m_shader->set_vector("YGain", 3, &options->chroma_y_gain[0]);
 			break;

src/tools/imgtool/modules/psion.cpp

@@ -245,6 +245,7 @@ char *stream_getline(imgtool::stream &source, uint16_t max_len)
 				source.read(&data, 1);
 				if (data != '\n')
 					source.seek(-1, SEEK_CUR);
+				[[fallthrough]];
 			case '\n':
 				return line;
 			default: