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add the const operand to docs for inline assembly #1556

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Aug 14, 2024
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add the const operand to docs for inline assembly #1556

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8 changes: 6 additions & 2 deletions src/inline-assembly.md
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Original file line number Diff line number Diff line change
Expand Up @@ -54,7 +54,7 @@ format_string := STRING_LITERAL / RAW_STRING_LITERAL
dir_spec := "in" / "out" / "lateout" / "inout" / "inlateout"
reg_spec := <register class> / "\"" <explicit register> "\""
operand_expr := expr / "_" / expr "=>" expr / expr "=>" "_"
reg_operand := [ident "="] dir_spec "(" reg_spec ")" operand_expr
reg_operand := [ident "="] dir_spec "(" reg_spec ")" operand_expr / sym <path> / const <expr>
clobber_abi := "clobber_abi(" <abi> *("," <abi>) [","] ")"
option := "pure" / "nomem" / "readonly" / "preserves_flags" / "noreturn" / "nostack" / "att_syntax" / "raw"
options := "options(" option *("," option) [","] ")"
Expand Down Expand Up @@ -174,14 +174,18 @@ r[asm.operand-type.supported-operands.sym]
- A mangled symbol name referring to the item is substituted into the asm template string.
- The substituted string does not include any modifiers (e.g. GOT, PLT, relocations, etc).
- `<path>` is allowed to point to a `#[thread_local]` static, in which case the asm code can combine the symbol with relocations (e.g. `@plt`, `@TPOFF`) to read from thread-local data.
* `const <expr>`
- `<expr>` must be an integer constant expression. This expression follows the same rules as inline `const` blocks.
- The type of the expression may be any integer type, but defaults to `i32` just like integer literals.
- The value of the expression is formatted as a string and substituted directly into the asm template string.

r[asm.operand-type.left-to-right]
Operand expressions are evaluated from left to right, just like function call arguments.
After the `asm!` has executed, outputs are written to in left to right order.
This is significant if two outputs point to the same place: that place will contain the value of the rightmost output.

r[asm.operand-type.global_asm-restriction]
Since `global_asm!` exists outside a function, it can only use `sym` operands.
Since `global_asm!` exists outside a function, it can only use `sym` and `const` operands.

## Register operands

Expand Down