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Rollup merge of #98337 - c410-f3r:assert-compiler, r=oli-obk

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[RFC 2011] Optimize non-consuming operators

Tracking issue: https://github.com/rust-lang/rust/issues/44838
Fifth step of https://github.com/rust-lang/rust/pull/96496

The most non-invasive approach that will probably have very little to no performance impact.

## Current behaviour

Captures are handled "on-the-fly", i.e., they are performed in the same place expressions are located.

```rust
// `let a = 1; let b = 2; assert!(a > 1 && b < 100);`

if !(
  { ***try capture `a` and then return `a`*** } > 1 && { ***try capture `b` and then return `b`*** } < 100
) {
  panic!( ... );
}
```

As such, some overhead is likely to occur (Specially with very large chains of conditions).

## New behaviour for non-consuming operators

When an operator is known to not take `self`, then it is possible to capture variables **AFTER** the condition.

```rust
// `let a = 1; let b = 2; assert!(a > 1 && b < 100);`

if !( a > 1 && b < 100 ) {
  { ***try capture `a`*** }
  { ***try capture `b`*** }
  panic!( ... );
}
```

So the possible impact on the runtime execution time will be diminished.

r? ````@oli-obk````
This commit is contained in:
Dylan DPC 2022-06-28 15:30:02 +05:30 • committed by GitHub
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5 changed files with 260 additions and 53 deletions
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96
compiler/rustc_builtin_macros/src/assert/context.rs
View file

@ -1,11 +1,10 @@
use crate::assert::expr_if_not;
use rustc_ast::{
attr,
ptr::P,
token,
tokenstream::{DelimSpan, TokenStream, TokenTree},
BorrowKind, Expr, ExprKind, ItemKind, MacArgs, MacCall, MacDelimiter, Mutability, Path,
PathSegment, Stmt, StructRest, UseTree, UseTreeKind, DUMMY_NODE_ID,
BinOpKind, BorrowKind, Expr, ExprKind, ItemKind, MacArgs, MacCall, MacDelimiter, Mutability,
Path, PathSegment, Stmt, StructRest, UnOp, UseTree, UseTreeKind, DUMMY_NODE_ID,
};
use rustc_ast_pretty::pprust;
use rustc_data_structures::fx::FxHashSet;
@ -16,11 +15,19 @@ use rustc_span::{
};
pub(super) struct Context<'cx, 'a> {
// An optimization.
//
// Elements that aren't consumed (PartialEq, PartialOrd, ...) can be copied **after** the
// `assert!` expression fails rather than copied on-the-fly.
best_case_captures: Vec<Stmt>,
// Top-level `let captureN = Capture::new()` statements
capture_decls: Vec<Capture>,
cx: &'cx ExtCtxt<'a>,
// Formatting string used for debugging
fmt_string: String,
// If the current expression being visited consumes itself. Used to construct
// `best_case_captures`.
is_consumed: bool,
// Top-level `let __local_bindN = &expr` statements
local_bind_decls: Vec<Stmt>,
// Used to avoid capturing duplicated paths
@ -36,9 +43,11 @@ pub(super) struct Context<'cx, 'a> {
impl<'cx, 'a> Context<'cx, 'a> {
pub(super) fn new(cx: &'cx ExtCtxt<'a>, span: Span) -> Self {
Self {
best_case_captures: <_>::default(),
capture_decls: <_>::default(),
cx,
fmt_string: <_>::default(),
is_consumed: true,
local_bind_decls: <_>::default(),
paths: <_>::default(),
span,
@ -69,14 +78,22 @@ impl<'cx, 'a> Context<'cx, 'a> {
self.manage_cond_expr(&mut cond_expr);
let initial_imports = self.build_initial_imports();
let panic = self.build_panic(&expr_str, panic_path);
let cond_expr_with_unlikely = self.build_unlikely(cond_expr);
let Self { capture_decls, cx, local_bind_decls, span, .. } = self;
let Self { best_case_captures, capture_decls, cx, local_bind_decls, span, .. } = self;
let mut assert_then_stmts = Vec::with_capacity(2);
assert_then_stmts.extend(best_case_captures);
assert_then_stmts.push(self.cx.stmt_expr(panic));
let assert_then = self.cx.block(span, assert_then_stmts);
let mut stmts = Vec::with_capacity(4);
stmts.push(initial_imports);
stmts.extend(capture_decls.into_iter().map(|c| c.decl));
stmts.extend(local_bind_decls);
stmts.push(cx.stmt_expr(expr_if_not(cx, span, cond_expr, panic, None)));
stmts.push(
cx.stmt_expr(cx.expr(span, ExprKind::If(cond_expr_with_unlikely, assert_then, None))),
);
cx.expr_block(cx.block(span, stmts))
}
@ -115,6 +132,16 @@ impl<'cx, 'a> Context<'cx, 'a> {
)
}
/// Takes the conditional expression of `assert!` and then wraps it inside `unlikely`
fn build_unlikely(&self, cond_expr: P<Expr>) -> P<Expr> {
let unlikely_path = self.cx.std_path(&[sym::intrinsics, sym::unlikely]);
self.cx.expr_call(
self.span,
self.cx.expr_path(self.cx.path(self.span, unlikely_path)),
vec![self.cx.expr(self.span, ExprKind::Unary(UnOp::Not, cond_expr))],
)
}
/// The necessary custom `panic!(...)` expression.
///
/// panic!(
@ -167,17 +194,39 @@ impl<'cx, 'a> Context<'cx, 'a> {
/// See [Self::manage_initial_capture] and [Self::manage_try_capture]
fn manage_cond_expr(&mut self, expr: &mut P<Expr>) {
match (*expr).kind {
ExprKind::AddrOf(_, _, ref mut local_expr) => {
self.manage_cond_expr(local_expr);
ExprKind::AddrOf(_, mutability, ref mut local_expr) => {
self.with_is_consumed_management(
matches!(mutability, Mutability::Mut),
|this| this.manage_cond_expr(local_expr)
);
}
ExprKind::Array(ref mut local_exprs) => {
for local_expr in local_exprs {
self.manage_cond_expr(local_expr);
}
}
ExprKind::Binary(_, ref mut lhs, ref mut rhs) => {
self.manage_cond_expr(lhs);
self.manage_cond_expr(rhs);
ExprKind::Binary(ref op, ref mut lhs, ref mut rhs) => {
self.with_is_consumed_management(
matches!(
op.node,
BinOpKind::Add
| BinOpKind::And
| BinOpKind::BitAnd
| BinOpKind::BitOr
| BinOpKind::BitXor
| BinOpKind::Div
| BinOpKind::Mul
| BinOpKind::Or
| BinOpKind::Rem
| BinOpKind::Shl
| BinOpKind::Shr
| BinOpKind::Sub
),
|this| {
this.manage_cond_expr(lhs);
this.manage_cond_expr(rhs);
}
);
}
ExprKind::Call(_, ref mut local_exprs) => {
for local_expr in local_exprs {
@ -228,8 +277,11 @@ impl<'cx, 'a> Context<'cx, 'a> {
self.manage_cond_expr(local_expr);
}
}
ExprKind::Unary(_, ref mut local_expr) => {
self.manage_cond_expr(local_expr);
ExprKind::Unary(un_op, ref mut local_expr) => {
self.with_is_consumed_management(
matches!(un_op, UnOp::Neg | UnOp::Not),
|this| this.manage_cond_expr(local_expr)
);
}
// Expressions that are not worth or can not be captured.
//
@ -337,9 +389,23 @@ impl<'cx, 'a> Context<'cx, 'a> {
))
.add_trailing_semicolon();
let local_bind_path = self.cx.expr_path(Path::from_ident(local_bind));
let ret = self.cx.stmt_expr(local_bind_path);
let block = self.cx.expr_block(self.cx.block(self.span, vec![try_capture_call, ret]));
*expr = self.cx.expr_deref(self.span, block);
let rslt = if self.is_consumed {
let ret = self.cx.stmt_expr(local_bind_path);
self.cx.expr_block(self.cx.block(self.span, vec![try_capture_call, ret]))
} else {
self.best_case_captures.push(try_capture_call);
local_bind_path
};
*expr = self.cx.expr_deref(self.span, rslt);
}
// Calls `f` with the internal `is_consumed` set to `curr_is_consumed` and then
// sets the internal `is_consumed` back to its original value.
fn with_is_consumed_management(&mut self, curr_is_consumed: bool, f: impl FnOnce(&mut Self)) {
let prev_is_consumed = self.is_consumed;
self.is_consumed = curr_is_consumed;
f(self);
self.is_consumed = prev_is_consumed;
}
}