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Add documentation for -Zverbose-asm

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This commit is contained in:
Trevor Gross 2024-06-21 14:17:47 -05:00
parent c15a698f56
commit 1a6893e14b
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src/doc/unstable-book/src/compiler-flags/verbose-asm.md Normal file
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# `verbose-asm`
The tracking issue for this feature is: [#126802](https://github.com/rust-lang/rust/issues/126802).
------------------------
This enables passing `-Zverbose-asm` to get contextual comments added by LLVM.
Sample code:
```rust
#[no_mangle]
pub fn foo(a: i32, b: i32) -> i32 {
a + b
}
```
Default output:
```asm
foo:
push rax
add edi, esi
mov dword ptr [rsp + 4], edi
seto al
jo .LBB0_2
mov eax, dword ptr [rsp + 4]
pop rcx
ret
.LBB0_2:
lea rdi, [rip + .L__unnamed_1]
mov rax, qword ptr [rip + core::panicking::panic_const::panic_const_add_overflow::h9c85248fe0d735b2@GOTPCREL]
call rax
.L__unnamed_2:
.ascii "/app/example.rs"
.L__unnamed_1:
.quad .L__unnamed_2
.asciz "\017\000\000\000\000\000\000\000\004\000\000\000\005\000\000"
```
With `-Zverbose-asm`:
```asm
foo: # @foo
# %bb.0:
push rax
add edi, esi
mov dword ptr [rsp + 4], edi # 4-byte Spill
seto al
jo .LBB0_2
# %bb.1:
mov eax, dword ptr [rsp + 4] # 4-byte Reload
pop rcx
ret
.LBB0_2:
lea rdi, [rip + .L__unnamed_1]
mov rax, qword ptr [rip + core::panicking::panic_const::panic_const_add_overflow::h9c85248fe0d735b2@GOTPCREL]
call rax
# -- End function
.L__unnamed_2:
.ascii "/app/example.rs"
.L__unnamed_1:
.quad .L__unnamed_2
.asciz "\017\000\000\000\000\000\000\000\004\000\000\000\005\000\000"
# DW_AT_external
```