asm_experimental_arch
The tracking issue for this feature is: #93335
This feature tracks asm! and global_asm! support for the following architectures:
- NVPTX
- PowerPC
- Hexagon
- MIPS32r2 and MIPS64r2
- wasm32
- BPF
- SPIR-V
- AVR
- MSP430
- M68k
- CSKY
- s390x
Register classes
| Architecture | Register class | Registers | LLVM constraint code |
|---|---|---|---|
| MIPS | reg | $[2-25] | r |
| MIPS | freg | $f[0-31] | f |
| NVPTX | reg16 | None* | h |
| NVPTX | reg32 | None* | r |
| NVPTX | reg64 | None* | l |
| Hexagon | reg | r[0-28] | r |
| PowerPC | reg | r[0-31] | r |
| PowerPC | reg_nonzero | r[1-31] | b |
| PowerPC | freg | f[0-31] | f |
| PowerPC | cr | cr[0-7], cr | Only clobbers |
| PowerPC | xer | xer | Only clobbers |
| wasm32 | local | None* | r |
| BPF | reg | r[0-10] | r |
| BPF | wreg | w[0-10] | w |
| AVR | reg | r[2-25], XH, XL, ZH, ZL | r |
| AVR | reg_upper | r[16-25], XH, XL, ZH, ZL | d |
| AVR | reg_pair | r3r2 .. r25r24, X, Z | r |
| AVR | reg_iw | r25r24, X, Z | w |
| AVR | reg_ptr | X, Z | e |
| MSP430 | reg | r[0-15] | r |
| M68k | reg | d[0-7], a[0-7] | r |
| M68k | reg_data | d[0-7] | d |
| M68k | reg_addr | a[0-3] | a |
| CSKY | reg | r[0-31] | r |
| CSKY | freg | f[0-31] | f |
| s390x | reg | r[0-10], r[12-14] | r |
| s390x | freg | f[0-15] | f |
Notes:
NVPTX doesn't have a fixed register set, so named registers are not supported.
WebAssembly doesn't have registers, so named registers are not supported.
Register class supported types
| Architecture | Register class | Target feature | Allowed types |
|---|---|---|---|
| MIPS32 | reg | None | i8, i16, i32, f32 |
| MIPS32 | freg | None | f32, f64 |
| MIPS64 | reg | None | i8, i16, i32, i64, f32, f64 |
| MIPS64 | freg | None | f32, f64 |
| NVPTX | reg16 | None | i8, i16 |
| NVPTX | reg32 | None | i8, i16, i32, f32 |
| NVPTX | reg64 | None | i8, i16, i32, f32, i64, f64 |
| Hexagon | reg | None | i8, i16, i32, f32 |
| PowerPC | reg | None | i8, i16, i32 |
| PowerPC | reg_nonzero | None | i8, i16, i32 |
| PowerPC | freg | None | f32, f64 |
| PowerPC | cr | N/A | Only clobbers |
| PowerPC | xer | N/A | Only clobbers |
| wasm32 | local | None | i8 i16 i32 i64 f32 f64 |
| BPF | reg | None | i8 i16 i32 i64 |
| BPF | wreg | alu32 | i8 i16 i32 |
| AVR | reg, reg_upper | None | i8 |
| AVR | reg_pair, reg_iw, reg_ptr | None | i16 |
| MSP430 | reg | None | i8, i16 |
| M68k | reg, reg_addr | None | i16, i32 |
| M68k | reg_data | None | i8, i16, i32 |
| CSKY | reg | None | i8, i16, i32 |
| CSKY | freg | None | f32, |
| s390x | reg, reg_addr | None | i8, i16, i32, i64 |
| s390x | freg | None | f32, f64 |
Register aliases
| Architecture | Base register | Aliases |
|---|---|---|
| Hexagon | r29 | sp |
| Hexagon | r30 | fr |
| Hexagon | r31 | lr |
| BPF | r[0-10] | w[0-10] |
| AVR | XH | r27 |
| AVR | XL | r26 |
| AVR | ZH | r31 |
| AVR | ZL | r30 |
| MSP430 | r0 | pc |
| MSP430 | r1 | sp |
| MSP430 | r2 | sr |
| MSP430 | r3 | cg |
| MSP430 | r4 | fp |
| M68k | a5 | bp |
| M68k | a6 | fp |
| M68k | a7 | sp, usp, ssp, isp |
| CSKY | r[0-3] | a[0-3] |
| CSKY | r[4-11] | l[0-7] |
| CSKY | r[12-13] | t[0-1] |
| CSKY | r14 | sp |
| CSKY | r15 | lr |
| CSKY | r[16-17] | l[8-9] |
| CSKY | r[18-25] | t[2-9] |
| CSKY | r28 | rgb |
| CSKY | r29 | rtb |
| CSKY | r30 | svbr |
| CSKY | r31 | tls |
Notes:
- TI does not mandate a frame pointer for MSP430, but toolchains are allowed to use one; LLVM uses
r4.
Unsupported registers
| Architecture | Unsupported register | Reason |
|---|---|---|
| All | sp, r15 (s390x) | The stack pointer must be restored to its original value at the end of an asm code block. |
| All | fr (Hexagon), $fp (MIPS), Y (AVR), r4 (MSP430), a6 (M68k), r11 (s390x) | The frame pointer cannot be used as an input or output. |
| All | r19 (Hexagon) | This is used internally by LLVM as a "base pointer" for functions with complex stack frames. |
| MIPS | $0 or $zero | This is a constant zero register which can't be modified. |
| MIPS | $1 or $at | Reserved for assembler. |
| MIPS | $26/$k0, $27/$k1 | OS-reserved registers. |
| MIPS | $28/$gp | Global pointer cannot be used as inputs or outputs. |
| MIPS | $ra | Return address cannot be used as inputs or outputs. |
| Hexagon | lr | This is the link register which cannot be used as an input or output. |
| AVR | r0, r1, r1r0 | Due to an issue in LLVM, the r0 and r1 registers cannot be used as inputs or outputs. If modified, they must be restored to their original values before the end of the block. |
| MSP430 | r0, r2, r3 | These are the program counter, status register, and constant generator respectively. Neither the status register nor constant generator can be written to. |
| M68k | a4, a5 | Used internally by LLVM for the base pointer and global base pointer. |
| CSKY | r7, r28 | Used internally by LLVM for the base pointer and global base pointer. |
| CSKY | r8 | Used internally by LLVM for the frame pointer. |
| CSKY | r14 | Used internally by LLVM for the stack pointer. |
| CSKY | r15 | This is the link register. |
| CSKY | r[26-30] | Reserved by its ABI. |
| CSKY | r31 | This is the TLS register. |
Template modifiers
| Architecture | Register class | Modifier | Example output | LLVM modifier |
|---|---|---|---|---|
| MIPS | reg | None | $2 | None |
| MIPS | freg | None | $f0 | None |
| NVPTX | reg16 | None | rs0 | None |
| NVPTX | reg32 | None | r0 | None |
| NVPTX | reg64 | None | rd0 | None |
| Hexagon | reg | None | r0 | None |
| PowerPC | reg | None | 0 | None |
| PowerPC | reg_nonzero | None | 3 | None |
| PowerPC | freg | None | 0 | None |
| s390x | reg | None | %r0 | None |
| s390x | reg_addr | None | %r1 | None |
| s390x | freg | None | %f0 | None |
| CSKY | reg | None | r0 | None |
| CSKY | freg | None | f0 | None |
Flags covered by preserves_flags
These flags registers must be restored upon exiting the asm block if the preserves_flags option is set:
- AVR
- The status register
SREG.
- The status register
- MSP430
- The status register
r2.
- The status register
- M68k
- The condition code register
ccr.
- The condition code register
- s390x
- The condition code register
cc.
- The condition code register