在机器代码方面，在GCC、clang和/或LLVM中实现的架构支持在哪里？

Question

我在看this

Architecture characteristic key
-----------------------------------------------------------------------
H       A hardware implementation does not exist.
M       A hardware implementation is not currently being manufactured.
S       A Free simulator does not exist.
L       Integer registers are narrower than 32 bits.
Q       Integer registers are at least 64 bits wide.
N       Memory is not byte addressable, and/or bytes are not eight bits.
F       Floating point arithmetic is not included in the instruction set
I       Architecture does not use IEEE format floating point numbers
C       Architecture does not have a single condition code register.
B       Architecture has delay slots.
D       Architecture has a stack that grows upward.

l       Port cannot use ILP32 mode integer arithmetic.
q       Port can use LP64 mode integer arithmetic.
r       Port can switch between ILP32 and LP64 at runtime.
        (Not necessarily supported by all subtargets.)
c       Port uses cc0.
p       Port uses define_peephole (as opposed to define_peephole2).
b       Port uses '"* ..."' notation for output template code.
f       Port does not define prologue and/or epilogue RTL expanders.
m       Port does not use define_constants.
g       Port does not define TARGET_ASM_FUNCTION_(PRO|EPI)LOGUE.
i       Port generates multiple inheritance thunks using
        TARGET_ASM_OUTPUT_MI(_VCALL)_THUNK.
a       Port uses LRA (by default, i.e. unless overridden by a switch).
t       All insns either produce exactly one assembly instruction, or
        trigger a define_split.
e       <arch>-elf is not a supported target.
s       <arch>-elf is the correct target to use with the simulator
        in /cvs/src.
          |      Characteristics
Target     | HMSLQNFICBD lqrcpbfmgiates
-----------+---------------------------
aarch64    |     Q        q   b  gia  s
alpha      |  ?  Q   C    q     mgi  e
arc        |          B       b  gia
arm        |                  b   ia  s
avr        |    L  FI    l  cp   g
bfin       |       F             gi
c6x        |   S     CB          gi
cr16       |    L  F C      c    g    s
cris       |       F  B          gi   s
csky       |                  b   ia
epiphany   |         C           gi   s
fr30       | ??    FI B      pb mg    s
frv        | ??       B       b   i   s
gcn        |   S     C D  q        a e
h8300      |       FI B          g    s
i386       |     Q        q   b   ia
ia64       |   ? Q   C    qr  b m i
iq2000     | ???   FICB       b  g  t
lm32       |       F             g
m32c       |    L  FI    l    b  g    s
m32r       |       FI         b       s
m68k       |                 pb   i
mcore      |  ?    FI        pb mg    s
mep        |       F C        b  g  t s
microblaze |         CB           i   s
mips       |     Q   CB   qr      ia  s
mmix       | HM  Q   C    q       i  e
mn10300    | ??                  gi   s
moxie      |       F             g  t s
msp430     |    L  FI    l    b  g    s
nds32      |       F C            ia  s
nios2      |         C            ia
nvptx      |   S Q   C    q     mg   e
pa         |     Q   CBD  qr  b   i  e
pdp11      |    L   IC    qr  b      e
powerpcspe |     Q   C    qr pb   ia
pru        |    L  F               a  s
riscv      |     Q   C    qr     gia
rl78       |    L  F     l       g    s
rs6000     |     Q   C    qr pb   ia
rx         |                          s
s390       |     Q        qr     gia e
sh         |     Q   CB   qr p    i
sparc      |     Q   CB   qr  b   ia
stormy16   | ???L  FIC D l    b   i
tilegx     |     Q   C    q      gi  e
tilepro    |   S   F C           gi  e
v850       |                     g a  s
vax        |  M     I         b   i  e
visium     |          B          g  t s
xtensa     |         C

这看起来像是大约50个架构。在GitHub上的源代码中实现的所有这些都在哪里？对于GCC、clang和/或LLVM (或在实现架构集成方面可能感兴趣的任何其他关键项目)。

Answer 1

对于LLVM (Clang是基于LLVM的前端)，您可以在llvm/lib/Target/目录中找到每个架构的后端代码。LLVM使用.td目标描述文件来描述目标(它是一种自己的语言)。比如指令、寄存器、调用约定等等。

在这些目录中还有实现某些功能的.cpp文件。例如，llvm/lib/Target/Mips/MipsDelaySlotFiller.cpp文件实现了一个通道，用Mips体系结构的有用指令填充延迟空位。

有用于添加RISC-V目标的git补丁的this存储库，这是一个很好的例子，如何逐步实现后端。is也有很多文档，但请记住，它已经相当过时了，但仍然有有用的信息。

Answer 2

非常简短地概述了一下GCC：

GCC的.md机器定义文件使用与GNU内联asm类似的约束语法，告诉它哪些指令是可用的，以及它们做了什么。(GCC不知道机器代码，只知道asm文本，这就是为什么它只能输出一个.s供as单独汇编。)还有一些C函数知道该体系结构的通用规则，我猜是寄存器名称之类的东西。

《GCC -内幕》手册中有一节6.3.9 Anatomy of a Target Back End，记录了相关文件在GCC源代码树中的位置。