Implement new asm! syntax from RFC 2850
This PR implements the new `asm!` syntax proposed in https://github.com/rust-lang/rfcs/pull/2850.
# Design
A large part of this PR revolves around taking an `asm!` macro invocation and plumbing it through all of the compiler layers down to LLVM codegen. Throughout the various stages, an `InlineAsm` generally consists of 3 components:
- The template string, which is stored as an array of `InlineAsmTemplatePiece`. Each piece represents either a literal or a placeholder for an operand (just like format strings).
```rust
pub enum InlineAsmTemplatePiece {
String(String),
Placeholder { operand_idx: usize, modifier: Option<char>, span: Span },
}
```
- The list of operands to the `asm!` (`in`, `[late]out`, `in[late]out`, `sym`, `const`). These are represented differently at each stage of lowering, but follow a common pattern:
- `in`, `out` and `inout` all have an associated register class (`reg`) or explicit register (`"eax"`).
- `inout` has 2 forms: one with a single expression that is both read from and written to, and one with two separate expressions for the input and output parts.
- `out` and `inout` have a `late` flag (`lateout` / `inlateout`) to indicate that the register allocator is allowed to reuse an input register for this output.
- `out` and the split variant of `inout` allow `_` to be specified for an output, which means that the output is discarded. This is used to allocate scratch registers for assembly code.
- `sym` is a bit special since it only accepts a path expression, which must point to a `static` or a `fn`.
- The options set at the end of the `asm!` macro. The only one that is particularly of interest to rustc is `NORETURN` which makes `asm!` return `!` instead of `()`.
```rust
bitflags::bitflags! {
pub struct InlineAsmOptions: u8 {
const PURE = 1 << 0;
const NOMEM = 1 << 1;
const READONLY = 1 << 2;
const PRESERVES_FLAGS = 1 << 3;
const NORETURN = 1 << 4;
const NOSTACK = 1 << 5;
}
}
```
## AST
`InlineAsm` is represented as an expression in the AST:
```rust
pub struct InlineAsm {
pub template: Vec<InlineAsmTemplatePiece>,
pub operands: Vec<(InlineAsmOperand, Span)>,
pub options: InlineAsmOptions,
}
pub enum InlineAsmRegOrRegClass {
Reg(Symbol),
RegClass(Symbol),
}
pub enum InlineAsmOperand {
In {
reg: InlineAsmRegOrRegClass,
expr: P<Expr>,
},
Out {
reg: InlineAsmRegOrRegClass,
late: bool,
expr: Option<P<Expr>>,
},
InOut {
reg: InlineAsmRegOrRegClass,
late: bool,
expr: P<Expr>,
},
SplitInOut {
reg: InlineAsmRegOrRegClass,
late: bool,
in_expr: P<Expr>,
out_expr: Option<P<Expr>>,
},
Const {
expr: P<Expr>,
},
Sym {
expr: P<Expr>,
},
}
```
The `asm!` macro is implemented in librustc_builtin_macros and outputs an `InlineAsm` AST node. The template string is parsed using libfmt_macros, positional and named operands are resolved to explicit operand indicies. Since target information is not available to macro invocations, validation of the registers and register classes is deferred to AST lowering.
## HIR
`InlineAsm` is represented as an expression in the HIR:
```rust
pub struct InlineAsm<'hir> {
pub template: &'hir [InlineAsmTemplatePiece],
pub operands: &'hir [InlineAsmOperand<'hir>],
pub options: InlineAsmOptions,
}
pub enum InlineAsmRegOrRegClass {
Reg(InlineAsmReg),
RegClass(InlineAsmRegClass),
}
pub enum InlineAsmOperand<'hir> {
In {
reg: InlineAsmRegOrRegClass,
expr: Expr<'hir>,
},
Out {
reg: InlineAsmRegOrRegClass,
late: bool,
expr: Option<Expr<'hir>>,
},
InOut {
reg: InlineAsmRegOrRegClass,
late: bool,
expr: Expr<'hir>,
},
SplitInOut {
reg: InlineAsmRegOrRegClass,
late: bool,
in_expr: Expr<'hir>,
out_expr: Option<Expr<'hir>>,
},
Const {
expr: Expr<'hir>,
},
Sym {
expr: Expr<'hir>,
},
}
```
AST lowering is where `InlineAsmRegOrRegClass` is converted from `Symbol`s to an actual register or register class. If any modifiers are specified for a template string placeholder, these are validated against the set allowed for that operand type. Finally, explicit registers for inputs and outputs are checked for conflicts (same register used for different operands).
## Type checking
Each register class has a whitelist of types that it may be used with. After the types of all operands have been determined, the `intrinsicck` pass will check that these types are in the whitelist. It also checks that split `inout` operands have compatible types and that `const` operands are integers or floats. Suggestions are emitted where needed if a template modifier should be used for an operand based on the type that was passed into it.
## HAIR
`InlineAsm` is represented as an expression in the HAIR:
```rust
crate enum ExprKind<'tcx> {
// [..]
InlineAsm {
template: &'tcx [InlineAsmTemplatePiece],
operands: Vec<InlineAsmOperand<'tcx>>,
options: InlineAsmOptions,
},
}
crate enum InlineAsmOperand<'tcx> {
In {
reg: InlineAsmRegOrRegClass,
expr: ExprRef<'tcx>,
},
Out {
reg: InlineAsmRegOrRegClass,
late: bool,
expr: Option<ExprRef<'tcx>>,
},
InOut {
reg: InlineAsmRegOrRegClass,
late: bool,
expr: ExprRef<'tcx>,
},
SplitInOut {
reg: InlineAsmRegOrRegClass,
late: bool,
in_expr: ExprRef<'tcx>,
out_expr: Option<ExprRef<'tcx>>,
},
Const {
expr: ExprRef<'tcx>,
},
SymFn {
expr: ExprRef<'tcx>,
},
SymStatic {
expr: ExprRef<'tcx>,
},
}
```
The only significant change compared to HIR is that `Sym` has been lowered to either a `SymFn` whose `expr` is a `Literal` ZST of the `fn`, or a `SymStatic` whose `expr` is a `StaticRef`.
## MIR
`InlineAsm` is represented as a `Terminator` in the MIR:
```rust
pub enum TerminatorKind<'tcx> {
// [..]
/// Block ends with an inline assembly block. This is a terminator since
/// inline assembly is allowed to diverge.
InlineAsm {
/// The template for the inline assembly, with placeholders.
template: &'tcx [InlineAsmTemplatePiece],
/// The operands for the inline assembly, as `Operand`s or `Place`s.
operands: Vec<InlineAsmOperand<'tcx>>,
/// Miscellaneous options for the inline assembly.
options: InlineAsmOptions,
/// Destination block after the inline assembly returns, unless it is
/// diverging (InlineAsmOptions::NORETURN).
destination: Option<BasicBlock>,
},
}
pub enum InlineAsmOperand<'tcx> {
In {
reg: InlineAsmRegOrRegClass,
value: Operand<'tcx>,
},
Out {
reg: InlineAsmRegOrRegClass,
late: bool,
place: Option<Place<'tcx>>,
},
InOut {
reg: InlineAsmRegOrRegClass,
late: bool,
in_value: Operand<'tcx>,
out_place: Option<Place<'tcx>>,
},
Const {
value: Operand<'tcx>,
},
SymFn {
value: Box<Constant<'tcx>>,
},
SymStatic {
value: Box<Constant<'tcx>>,
},
}
```
As part of HAIR lowering, `InOut` and `SplitInOut` operands are lowered to a split form with a separate `in_value` and `out_place`.
Semantically, the `InlineAsm` terminator is similar to the `Call` terminator except that it has multiple output places where a `Call` only has a single return place output.
The constant promotion pass is used to ensure that `const` operands are actually constants (using the same logic as `#[rustc_args_required_const]`).
## Codegen
Operands are lowered one more time before being passed to LLVM codegen:
```rust
pub enum InlineAsmOperandRef<'tcx, B: BackendTypes + ?Sized> {
In {
reg: InlineAsmRegOrRegClass,
value: OperandRef<'tcx, B::Value>,
},
Out {
reg: InlineAsmRegOrRegClass,
late: bool,
place: Option<PlaceRef<'tcx, B::Value>>,
},
InOut {
reg: InlineAsmRegOrRegClass,
late: bool,
in_value: OperandRef<'tcx, B::Value>,
out_place: Option<PlaceRef<'tcx, B::Value>>,
},
Const {
string: String,
},
SymFn {
instance: Instance<'tcx>,
},
SymStatic {
def_id: DefId,
},
}
```
The operands are lowered to LLVM operands and constraint codes as follow:
- `out` and the output part of `inout` operands are added first, as required by LLVM. Late output operands have a `=` prefix added to their constraint code, non-late output operands have a `=&` prefix added to their constraint code.
- `in` operands are added normally.
- `inout` operands are tied to the matching output operand.
- `sym` operands are passed as function pointers or pointers, using the `"s"` constraint.
- `const` operands are formatted to a string and directly inserted in the template string.
The template string is converted to LLVM form:
- `$` characters are escaped as `$$`.
- `const` operands are converted to strings and inserted directly.
- Placeholders are formatted as `${X:M}` where `X` is the operand index and `M` is the modifier character. Modifiers are converted from the Rust form to the LLVM form.
The various options are converted to clobber constraints or LLVM attributes, refer to the [RFC](https://github.com/Amanieu/rfcs/blob/inline-asm/text/0000-inline-asm.md#mapping-to-llvm-ir) for more details.
Note that LLVM is sometimes rather picky about what types it accepts for certain constraint codes so we sometimes need to insert conversions to/from a supported type. See the target-specific ISelLowering.cpp files in LLVM for details.
# Adding support for new architectures
Adding inline assembly support to an architecture is mostly a matter of defining the registers and register classes for that architecture. All the definitions for register classes are located in `src/librustc_target/asm/`.
Additionally you will need to implement lowering of these register classes to LLVM constraint codes in `src/librustc_codegen_llvm/asm.rs`.
Rename lint `identity_conversion` to `useless_conversion`
Lint name `identity_conversion` was misleading, so this PR renames it to `useless_conversion`.
As decision has not really came up in the issue comments, this PR will probably need discussion.
fixes#3106
changelog: Rename lint `identity_conversion` to `useless_conversion`
Rustup with git subtree
The commits from the last rustup #5587, are again included in this rustup, since I rebased the rustup. Lesson learned: never rebase, only merge when working with git subtree.
changelog: none
Merge some lints together
This PR merges following lints:
- `block_in_if_condition_expr` and `block_in_if_condition_stmt` → `blocks_in_if_conditions`
- `option_map_unwrap_or`, `option_map_unwrap_or_else` and `result_map_unwrap_or_else` → `map_unwrap`
- `option_unwrap_used` and `result_unwrap_used` → `unwrap_used`
- `option_expect_used` and `result_expect_used` → `expect_used`
- `wrong_pub_self_convention` into `wrong_self_convention`
- `for_loop_over_option` and `for_loop_over_result` → `for_loops_over_fallibles`
Lints that have already been merged since the issue was created:
- [x] `new_without_default` and `new_without_default_derive` → `new_without_default`
Need more discussion:
- `string_add` and `string_add_assign`: do we agree to merge them or not? Is there something more to do? → **not merge finally**
- `identity_op` and `modulo_one` → `useless_arithmetic`: seems outdated, since `modulo_arithmetic` has been created.
fixes#1078
changelog: Merging some lints together:
- `block_in_if_condition_expr` and `block_in_if_condition_stmt` → `blocks_in_if_conditions`
- `option_map_unwrap_or`, `option_map_unwrap_or_else` and `result_map_unwrap_or_else` → `map_unwrap_or`
- `option_unwrap_used` and `result_unwrap_used` → `unwrap_used`
- `option_expect_used` and `result_expect_used` → `expect_used`
- `for_loop_over_option` and `for_loop_over_result` → `for_loops_over_fallibles`
Literal error reporting cleanup
While doing some performance work, I noticed some code duplication in `librustc_parser/lexer/mod.rs`, so I cleaned it up.
This PR is probably best reviewed commit by commit.
I'm not sure what the API stability practices for `librustc_lexer` are. Four public methods in `unescape.rs` can be removed, but two are used by clippy, so I left them in for now.
I could open a PR for Rust-Analyzer when this one lands.
But how do I open a PR for clippy? (Git submodules are frustrating to work with)
identity_op: allow `1 << 0`
I went for accepting `1 << 0` verbatim instead of something more general as it seems to be what everyone in the issue thread needed.
changelog: identity_op: allow `1 << 0` as it's a common pattern in bit manipulation code.
Fixes#3430
rustc_driver: factor out computing the exit code
In a recent Miri PR I [added a convenience wrapper](https://github.com/rust-lang/miri/pull/1405/files#diff-c3d602c5c8035a16699ce9c015bfeceaR125) around `catch_fatal_errors` and `run_compiler` that @oli-obk suggested I could upstream. However, after seeing what could be shared between `rustc_driver::main`, clippy and Miri, really the only thing I found is computing the exit code -- so that's what this PR does.
What prevents using the Miri convenience function in `rustc_driver::main` and clippy is that they do extra work inside `catch_fatal_errors`, and while I could abstract that away, clippy actually *computes the callbacks* inside there, and I fond no good way to abstract that and thus gave up. Maybe the clippy thing could be moved out, I am not sure if it ever can actually raise a `FatalErrorMarker` -- someone more knowledgeable in clippy would have to do that.
Downgrade useless_let_if_seq to nursery
I feel that this lint has the wrong balance of incorrect suggestions for a default-enabled lint.
The immediate code I faced was something like:
```rust
fn main() {
let mut good = do1();
if !do2() {
good = false;
}
if good {
println!("good");
}
}
fn do1() -> bool { println!("1"); false }
fn do2() -> bool { println!("2"); false }
```
On this code Clippy calls it unidiomatic and suggests the following diff, which has different behavior in a way that I don't necessarily want.
```diff
- let mut good = do1();
- if !do2() {
- good = false;
- }
+ let good = if !do2() {
+ false
+ } else {
+ do1()
+ };
```
On exploring issues filed about this lint, I have found that other users have also struggled with inappropriate suggestions (https://github.com/rust-lang/rust-clippy/issues/4124, https://github.com/rust-lang/rust-clippy/issues/3043, https://github.com/rust-lang/rust-clippy/issues/2918, https://github.com/rust-lang/rust-clippy/issues/2176) and suggestions that make the code worse (https://github.com/rust-lang/rust-clippy/issues/3769, https://github.com/rust-lang/rust-clippy/issues/2749). Overall I believe that this lint is still at nursery quality for now and should not be enabled.
---
changelog: Remove useless_let_if_seq from default set of enabled lints
Reversed empty ranges
This lint checks range expressions with inverted limits which result in empty ranges. This includes also the ranges used to index slices.
The lint reverse_range_loop was covering iteration of reversed ranges in a for loop, which is a subset of what this new lint covers, so it has been removed. I'm not sure if that's the best choice. It would be doable to check in the new lint that we are not in the arguments of a for loop; I went for removing it because the logic was too similar to keep them separated.
changelog: Added reversed_empty_ranges lint that checks for ranges where the limits have been inverted, resulting in empty ranges. Removed reverse_range_loop which was covering a subset of the new lint.
Closes#4192Closes#96
