Fix inline asm register allocator corrupting rbx

[CathalMullan]

The register allocator can assign overlapping registers of rbx, corrupting the pointer used by the inline asm wrapper.

This fix marks bx as in-use to prevent this.

Encountered this while trying to run the Graviola test suite.

> cargo clif test --package graviola --lib -- low::tests::ct_equal

running 1 test
test low::tests::ct_equal ... FAILED

---- low::tests::ct_equal stderr ----

thread 'main' (210353) panicked at graviola/src/low/tests.rs:49:5:
assertion `left == right` failed
  left: false
 right: true

With this fix (and #1628, ctz/graviola#150), the entire Graviola test suite passes on x86_64, though 4 tests fail on AVX-512 hosts due to missing intrinsics.

[bjorn3]

I picked rbx as that isn't allowed as input or output register due to being reserved by LLVM, so I'm surprised bx even gets returned as allocatable register. https://github.com/rust-lang/rust/blob/ba1567989ee7774a1fb53aa680a8e4e8daa0f519/compiler/rustc_target/src/asm/x86.rs#L203-L217

[CathalMullan]

It's bl which doesn't seem to get filtered: https://github.com/rust-lang/rust/blob/main/compiler/rustc_target/src/asm/x86.rs#L253

Here's the full build logs for Graviola where it gets corrupted:

Details

warning: unsupported x86 llvm intrinsic llvm.x86.avx512.pternlog.d.128; replacing with trap

warning: unsupported x86 llvm intrinsic llvm.x86.avx512.pternlog.d.512; replacing with trap

warning: unsupported x86 llvm intrinsic llvm.x86.avx512.pternlog.q.512; replacing with trap

warning: unsupported x86 llvm intrinsic llvm.x86.avx512.pshuf.b.512; replacing with trap

warning: unsupported x86 llvm intrinsic llvm.x86.aesni.aesenc.512; replacing with trap

warning: unsupported x86 llvm intrinsic llvm.x86.aesni.aesenclast.512; replacing with trap

warning: unsupported x86 llvm intrinsic llvm.x86.pclmulqdq.512; replacing with trap

warning: `graviola` (lib test) generated 7 warnings
error: invalid operand for instruction
   |
note: instantiated into assembly here
  --> <inline asm>:14:8
   |
14 |        vpxor   y0, y0, y0
   |        ^

error: invalid operand for instruction
   |
note: instantiated into assembly here
  --> <inline asm>:17:8
   |
17 |        vmovdqu [rax], y0
   |        ^

error: aborting due to 2 previous errors

error: Failed to assemble `.globl _RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu11__zero_bytes__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0
       .type _RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu11__zero_bytes__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0,@function
       .section .text._RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu11__zero_bytes__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0,"ax",@progbits
       _RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu11__zero_bytes__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0:
       .intel_syntax noprefix
           push rbp
           mov rbp,rsp
           push rbx
           mov rbx,rdi
           mov rax, [rbx+0x0]
           mov rcx, [rbx+0x8]
              vpxor   y0, y0, y0
          2:  cmp rcx, 32
              jl  3f
              vmovdqu [rax], y0
              add rax, 32
              sub rcx, 32
              jmp 2b
          3:  sub rcx, 1
              jl  4f
              mov byte ptr [rax], 0
              add rax, 1
              jmp 3b
          4:
           pop rbx
           pop rbp
           ret
       .att_syntax
       .size _RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu11__zero_bytes__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0, .-_RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu11__zero_bytes__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0
       .text


       .globl _RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu15leave_cpu_state__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0
       .type _RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu15leave_cpu_state__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0,@function
       .section .text._RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu15leave_cpu_state__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0,"ax",@progbits
       _RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu15leave_cpu_state__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0:
       .intel_syntax noprefix
           push rbp
           mov rbp,rsp
           push rbx
           mov rbx,rdi
          vzeroall
           pop rbx
           pop rbp
           ret
       .att_syntax
       .size _RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu15leave_cpu_state__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0, .-_RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu15leave_cpu_state__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0
       .text


       .globl _RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu16ct_compare_bytes__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0
       .type _RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu16ct_compare_bytes__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0,@function
       .section .text._RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu16ct_compare_bytes__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0,"ax",@progbits
       _RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu16ct_compare_bytes__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0:
       .intel_syntax noprefix
           push rbp
           mov rbp,rsp
           push rbx
           mov rbx,rdi
           mov [rbx+0x0], bl
           mov rax, [rbx+0x8]
           mov rcx, [rbx+0x10]
           mov rdx, [rbx+0x18]
           mov bl, [rbx+0x20]
           mov sil, [rbx+0x1]
          2: cmp rdx, 0
             je  3f
             mov bl, [rax]
             xor bl, [rcx]
             or  sil, bl
             add rax, 1
             add rcx, 1
             sub rdx, 1
             jmp 2b
          3:
           mov [rbx+0x1], sil
           mov bl, [rbx+0x0]
           pop rbx
           pop rbp
           ret
       .att_syntax
       .size _RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu16ct_compare_bytes__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0, .-_RNvNtNtNtCs1fs6YDMng9x_8graviola3low6x86_643cpu16ct_compare_bytes__inline_asm_9p5s6xwqy0njxb3man23ssxa5_n0
       .text


       `

warning: `graviola` (lib) generated 7 warnings (7 duplicates)
error: could not compile `graviola` (lib) due to 1 previous error; 7 warnings emitted

[bjorn3]

I think the issue is that bl and bh are missing % rbx_reserved at https://github.com/rust-lang/rust/blob/8ddf4ef064fb702fed0f3d239ec8d0bac607484e/compiler/rustc_target/src/asm/x86.rs#L253-L254 This would need to be fixed on the rustc side.