rust
/
reference
mirror of https://github.com/rust-lang/reference
1
0
Fork 0
Code Issues Releases Wiki Activity

nomem, readonly also means no fences

This commit is contained in:
Ralf Jung 2023-10-09 11:32:27 +02:00
parent 142b2ed77d
commit fae136ca7e
1 changed files with 2 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/inline-assembly.md
View File

@ -416,8 +416,10 @@ Currently the following options are defined:
This allows the compiler to execute the `asm!` block fewer times than specified in the program (e.g. by hoisting it out of a loop) or even eliminate it entirely if the outputs are not used.
- `nomem`: The `asm!` blocks does not read or write to any memory.
This allows the compiler to cache the values of modified global variables in registers across the `asm!` block since it knows that they are not read or written to by the `asm!`.
The compiler also assumes that this `asm!` block does not perform any kind of synchronization with other threads, e.g. via fences.
- `readonly`: The `asm!` block does not write to any memory.
This allows the compiler to cache the values of unmodified global variables in registers across the `asm!` block since it knows that they are not written to by the `asm!`.
The compiler also assumes that this `asm!` block does not perform any kind of synchronization with other threads, e.g. via fences.
- `preserves_flags`: The `asm!` block does not modify the flags register (defined in the rules below).
This allows the compiler to avoid recomputing the condition flags after the `asm!` block.
- `noreturn`: The `asm!` block never returns, and its return type is defined as `!` (never).