1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411
use crate::build::ForGuard::OutsideGuard;
use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder};
use rustc_middle::middle::region::Scope;
use rustc_middle::thir::*;
use rustc_middle::{mir::*, ty};
use rustc_span::Span;
impl<'a, 'tcx> Builder<'a, 'tcx> {
pub(crate) fn ast_block(
&mut self,
destination: Place<'tcx>,
block: BasicBlock,
ast_block: BlockId,
source_info: SourceInfo,
) -> BlockAnd<()> {
let Block {
region_scope,
opt_destruction_scope,
span,
ref stmts,
expr,
targeted_by_break,
safety_mode,
} = self.thir[ast_block];
let expr = expr.map(|expr| &self.thir[expr]);
self.in_opt_scope(opt_destruction_scope.map(|de| (de, source_info)), move |this| {
this.in_scope((region_scope, source_info), LintLevel::Inherited, move |this| {
if targeted_by_break {
this.in_breakable_scope(None, destination, span, |this| {
Some(this.ast_block_stmts(
destination,
block,
span,
&stmts,
expr,
safety_mode,
region_scope,
))
})
} else {
this.ast_block_stmts(
destination,
block,
span,
&stmts,
expr,
safety_mode,
region_scope,
)
}
})
})
}
fn ast_block_stmts(
&mut self,
destination: Place<'tcx>,
mut block: BasicBlock,
span: Span,
stmts: &[StmtId],
expr: Option<&Expr<'tcx>>,
safety_mode: BlockSafety,
region_scope: Scope,
) -> BlockAnd<()> {
let this = self;
// This convoluted structure is to avoid using recursion as we walk down a list
// of statements. Basically, the structure we get back is something like:
//
// let x = <init> in {
// expr1;
// let y = <init> in {
// expr2;
// expr3;
// ...
// }
// }
//
// The let bindings are valid till the end of block so all we have to do is to pop all
// the let-scopes at the end.
//
// First we build all the statements in the block.
let mut let_scope_stack = Vec::with_capacity(8);
let outer_source_scope = this.source_scope;
let outer_in_scope_unsafe = this.in_scope_unsafe;
// This scope information is kept for breaking out of the parent remainder scope in case
// one let-else pattern matching fails.
// By doing so, we can be sure that even temporaries that receive extended lifetime
// assignments are dropped, too.
let mut last_remainder_scope = region_scope;
this.update_source_scope_for_safety_mode(span, safety_mode);
let source_info = this.source_info(span);
for stmt in stmts {
let Stmt { ref kind, opt_destruction_scope } = this.thir[*stmt];
match kind {
StmtKind::Expr { scope, expr } => {
this.block_context.push(BlockFrame::Statement { ignores_expr_result: true });
unpack!(
block = this.in_opt_scope(
opt_destruction_scope.map(|de| (de, source_info)),
|this| {
let si = (*scope, source_info);
this.in_scope(si, LintLevel::Inherited, |this| {
this.stmt_expr(block, &this.thir[*expr], Some(*scope))
})
}
)
);
}
StmtKind::Let {
remainder_scope,
init_scope,
pattern,
initializer: Some(initializer),
lint_level,
else_block: Some(else_block),
span: _,
} => {
// When lowering the statement `let <pat> = <expr> else { <else> };`,
// the `<else>` block is nested in the parent scope enclosing this statement.
// That scope is usually either the enclosing block scope,
// or the remainder scope of the last statement.
// This is to make sure that temporaries instantiated in `<expr>` are dropped
// as well.
// In addition, even though bindings in `<pat>` only come into scope if
// the pattern matching passes, in the MIR building the storages for them
// are declared as live any way.
// This is similar to `let x;` statements without an initializer expression,
// where the value of `x` in this example may or may be assigned,
// because the storage for their values may not be live after all due to
// failure in pattern matching.
// For this reason, we declare those storages as live but we do not schedule
// any drop yet- they are scheduled later after the pattern matching.
// The generated MIR will have `StorageDead` whenever the control flow breaks out
// of the parent scope, regardless of the result of the pattern matching.
// However, the drops are inserted in MIR only when the control flow breaks out of
// the scope of the remainder scope associated with this `let .. else` statement.
// Pictorial explanation of the scope structure:
// ┌─────────────────────────────────┐
// │ Scope of the enclosing block, │
// │ or the last remainder scope │
// │ ┌───────────────────────────┐ │
// │ │ Scope for <else> block │ │
// │ └───────────────────────────┘ │
// │ ┌───────────────────────────┐ │
// │ │ Remainder scope of │ │
// │ │ this let-else statement │ │
// │ │ ┌─────────────────────┐ │ │
// │ │ │ <expr> scope │ │ │
// │ │ └─────────────────────┘ │ │
// │ │ extended temporaries in │ │
// │ │ <expr> lives in this │ │
// │ │ scope │ │
// │ │ ┌─────────────────────┐ │ │
// │ │ │ Scopes for the rest │ │ │
// │ │ └─────────────────────┘ │ │
// │ └───────────────────────────┘ │
// └─────────────────────────────────┘
// Generated control flow:
// │ let Some(x) = y() else { return; }
// │
// ┌────────▼───────┐
// │ evaluate y() │
// └────────┬───────┘
// │ ┌────────────────┐
// ┌────────▼───────┐ │Drop temporaries│
// │Test the pattern├──────►in y() │
// └────────┬───────┘ │because breaking│
// │ │out of <expr> │
// ┌────────▼───────┐ │scope │
// │Move value into │ └───────┬────────┘
// │binding x │ │
// └────────┬───────┘ ┌───────▼────────┐
// │ │Drop extended │
// ┌────────▼───────┐ │temporaries in │
// │Drop temporaries│ │<expr> because │
// │in y() │ │breaking out of │
// │because breaking│ │remainder scope │
// │out of <expr> │ └───────┬────────┘
// │scope │ │
// └────────┬───────┘ ┌───────▼────────┐
// │ │Enter <else> ├────────►
// ┌────────▼───────┐ │block │ return;
// │Continue... │ └────────────────┘
// └────────────────┘
let ignores_expr_result = matches!(pattern.kind, PatKind::Wild);
this.block_context.push(BlockFrame::Statement { ignores_expr_result });
// Lower the `else` block first because its parent scope is actually
// enclosing the rest of the `let .. else ..` parts.
let else_block_span = this.thir[*else_block].span;
// This place is not really used because this destination place
// should never be used to take values at the end of the failure
// block.
let dummy_place = this.temp(this.tcx.types.never, else_block_span);
let failure_entry = this.cfg.start_new_block();
let failure_block;
unpack!(
failure_block = this.ast_block(
dummy_place,
failure_entry,
*else_block,
this.source_info(else_block_span),
)
);
this.cfg.terminate(
failure_block,
this.source_info(else_block_span),
TerminatorKind::Unreachable,
);
// Declare the bindings, which may create a source scope.
let remainder_span = remainder_scope.span(this.tcx, this.region_scope_tree);
this.push_scope((*remainder_scope, source_info));
let_scope_stack.push(remainder_scope);
let visibility_scope =
Some(this.new_source_scope(remainder_span, LintLevel::Inherited, None));
let init = &this.thir[*initializer];
let initializer_span = init.span;
let failure = unpack!(
block = this.in_opt_scope(
opt_destruction_scope.map(|de| (de, source_info)),
|this| {
let scope = (*init_scope, source_info);
this.in_scope(scope, *lint_level, |this| {
this.declare_bindings(
visibility_scope,
remainder_span,
pattern,
None,
Some((Some(&destination), initializer_span)),
);
this.visit_primary_bindings(
pattern,
UserTypeProjections::none(),
&mut |this, _, _, _, node, span, _, _| {
this.storage_live_binding(
block,
node,
span,
OutsideGuard,
true,
);
},
);
this.ast_let_else(
block,
init,
initializer_span,
*else_block,
&last_remainder_scope,
pattern,
)
})
}
)
);
this.cfg.goto(failure, source_info, failure_entry);
if let Some(source_scope) = visibility_scope {
this.source_scope = source_scope;
}
last_remainder_scope = *remainder_scope;
}
StmtKind::Let { init_scope, initializer: None, else_block: Some(_), .. } => {
span_bug!(
init_scope.span(this.tcx, this.region_scope_tree),
"initializer is missing, but else block is present in this let binding",
)
}
StmtKind::Let {
remainder_scope,
init_scope,
ref pattern,
initializer,
lint_level,
else_block: None,
span: _,
} => {
let ignores_expr_result = matches!(pattern.kind, PatKind::Wild);
this.block_context.push(BlockFrame::Statement { ignores_expr_result });
// Enter the remainder scope, i.e., the bindings' destruction scope.
this.push_scope((*remainder_scope, source_info));
let_scope_stack.push(remainder_scope);
// Declare the bindings, which may create a source scope.
let remainder_span = remainder_scope.span(this.tcx, this.region_scope_tree);
let visibility_scope =
Some(this.new_source_scope(remainder_span, LintLevel::Inherited, None));
// Evaluate the initializer, if present.
if let Some(init) = initializer {
let init = &this.thir[*init];
let initializer_span = init.span;
unpack!(
block = this.in_opt_scope(
opt_destruction_scope.map(|de| (de, source_info)),
|this| {
let scope = (*init_scope, source_info);
this.in_scope(scope, *lint_level, |this| {
this.declare_bindings(
visibility_scope,
remainder_span,
pattern,
None,
Some((None, initializer_span)),
);
this.expr_into_pattern(block, &pattern, init)
// irrefutable pattern
})
},
)
)
} else {
let scope = (*init_scope, source_info);
unpack!(this.in_scope(scope, *lint_level, |this| {
this.declare_bindings(
visibility_scope,
remainder_span,
pattern,
None,
None,
);
block.unit()
}));
debug!("ast_block_stmts: pattern={:?}", pattern);
this.visit_primary_bindings(
pattern,
UserTypeProjections::none(),
&mut |this, _, _, _, node, span, _, _| {
this.storage_live_binding(block, node, span, OutsideGuard, true);
this.schedule_drop_for_binding(node, span, OutsideGuard);
},
)
}
// Enter the visibility scope, after evaluating the initializer.
if let Some(source_scope) = visibility_scope {
this.source_scope = source_scope;
}
last_remainder_scope = *remainder_scope;
}
}
let popped = this.block_context.pop();
assert!(popped.is_some_and(|bf| bf.is_statement()));
}
// Then, the block may have an optional trailing expression which is a “return” value
// of the block, which is stored into `destination`.
let tcx = this.tcx;
let destination_ty = destination.ty(&this.local_decls, tcx).ty;
if let Some(expr) = expr {
let tail_result_is_ignored =
destination_ty.is_unit() || this.block_context.currently_ignores_tail_results();
this.block_context
.push(BlockFrame::TailExpr { tail_result_is_ignored, span: expr.span });
unpack!(block = this.expr_into_dest(destination, block, expr));
let popped = this.block_context.pop();
assert!(popped.is_some_and(|bf| bf.is_tail_expr()));
} else {
// If a block has no trailing expression, then it is given an implicit return type.
// This return type is usually `()`, unless the block is diverging, in which case the
// return type is `!`. For the unit type, we need to actually return the unit, but in
// the case of `!`, no return value is required, as the block will never return.
// Opaque types of empty bodies also need this unit assignment, in order to infer that their
// type is actually unit. Otherwise there will be no defining use found in the MIR.
if destination_ty.is_unit()
|| matches!(destination_ty.kind(), ty::Alias(ty::Opaque, ..))
{
// We only want to assign an implicit `()` as the return value of the block if the
// block does not diverge. (Otherwise, we may try to assign a unit to a `!`-type.)
this.cfg.push_assign_unit(block, source_info, destination, this.tcx);
}
}
// Finally, we pop all the let scopes before exiting out from the scope of block
// itself.
for scope in let_scope_stack.into_iter().rev() {
unpack!(block = this.pop_scope((*scope, source_info), block));
}
// Restore the original source scope.
this.source_scope = outer_source_scope;
this.in_scope_unsafe = outer_in_scope_unsafe;
block.unit()
}
/// If we are entering an unsafe block, create a new source scope
fn update_source_scope_for_safety_mode(&mut self, span: Span, safety_mode: BlockSafety) {
debug!("update_source_scope_for({:?}, {:?})", span, safety_mode);
let new_unsafety = match safety_mode {
BlockSafety::Safe => return,
BlockSafety::BuiltinUnsafe => Safety::BuiltinUnsafe,
BlockSafety::ExplicitUnsafe(hir_id) => {
self.in_scope_unsafe = Safety::ExplicitUnsafe(hir_id);
Safety::ExplicitUnsafe(hir_id)
}
};
self.source_scope = self.new_source_scope(span, LintLevel::Inherited, Some(new_unsafety));
}
}