Bug in inline assembly for arm

[Sp00ph]

When trying to compile the gba crate(gba = { git = "https://github.com/rust-console/gba", rev = "127f31e" }) using the following target:

{
  "abi-blacklist": [
    "stdcall",
    "fastcall",
    "vectorcall",
    "thiscall",
    "win64",
    "sysv64"
  ],
  "arch": "arm",
  "atomic-cas": false,
  "cpu": "arm7tdmi",
  "data-layout": "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64",
  "emit-debug-gdb-scripts": false,
  "env": "agb",
  "executables": true,
  "features": "+soft-float,+strict-align",
  "linker": "arm-none-eabi-ld",
  "linker-flavor": "ld",
  "linker-is-gnu": true,
  "llvm-target": "thumbv4-none-agb",
  "os": "none",
  "panic-strategy": "abort",
  "pre-link-args-crt": {
        "ld": [
            "crt0.o"
        ]
    },
  "pre-link-args": {
    "ld": [
      "-Tlinker.ld"
    ]
  },
  "relocation-model": "static",
  "target-c-int-width": "32",
  "target-endian": "little",
  "target-pointer-width": "32",
  "vendor": "nintendo"
}

I get this compiler error:

error: invalid register `r9`: r9 is used internally by LLVM and cannot be used as an operand for inline asm
   --> C:\Users\anon\.cargo\git\checkouts\gba-4ba04b9d61fb788f\127f31e\src\sync\statics.rs:106:72
    |
106 |       out("r2") _, out("r3") _, out("r4") _, out("r5") _, out("r8") _, out("r9") _,
    |                                                                        ^^^^^^^^^^^

error: invalid register `r9`: r9 is used internally by LLVM and cannot be used as an operand for inline asm
   --> C:\Users\anon\.cargo\git\checkouts\gba-4ba04b9d61fb788f\127f31e\src\sync\statics.rs:113:72
    |
113 |       out("r2") _, out("r3") _, out("r4") _, out("r5") _, out("r8") _, out("r9") _,
    |                                                                        ^^^^^^^^^^^

error: invalid register `r9`: r9 is used internally by LLVM and cannot be used as an operand for inline asm
   --> C:\Users\anon\.cargo\git\checkouts\gba-4ba04b9d61fb788f\127f31e\src\sync\statics.rs:121:72
    |
121 |       out("r2") _, out("r3") _, out("r4") _, out("r5") _, out("r8") _, out("r9") _,
    |                                                                        ^^^^^^^^^^^

error: invalid register `r9`: r9 is used internally by LLVM and cannot be used as an operand for inline asm
   --> C:\Users\anon\.cargo\git\checkouts\gba-4ba04b9d61fb788f\127f31e\src\sync\statics.rs:129:72
    |
129 |       out("r2") _, out("r3") _, out("r4") _, out("r5") _, out("r8") _, out("r9") _,
    |                                                                        ^^^^^^^^^^^

error: aborting due to 4 previous errors

error: could not compile `gba`

This seems to be a bug in the asm! macro as this code used to compile just fine.

I'm using the latest nightly rustc release:

$ rustc --version --verbose
rustc 1.54.0-nightly (79e50bf77 2021-05-10)
binary: rustc
commit-hash: 79e50bf77928f374921a6bcafee3fcff1915f062
commit-date: 2021-05-10
host: x86_64-pc-windows-msvc
release: 1.54.0-nightly
LLVM version: 12.0.1

The same thing also happens when using the gnu toolchain:

$ rustc --version --verbose
rustc 1.54.0-nightly (79e50bf77 2021-05-10)
binary: rustc
commit-hash: 79e50bf77928f374921a6bcafee3fcff1915f062
commit-date: 2021-05-10
host: x86_64-pc-windows-gnu
release: 1.54.0-nightly
LLVM version: 12.0.1

[PatchMixolydic]

cc #85247, which has information about the commit that made r9 a reserved register

[Amanieu]

Closing as a duplicate of #85247