diff options
Diffstat (limited to 'compiler/rustc_mir_build')
| -rw-r--r-- | compiler/rustc_mir_build/src/build/expr/stmt.rs | 39 | ||||
| -rw-r--r-- | compiler/rustc_mir_build/src/build/scope.rs | 86 | ||||
| -rw-r--r-- | compiler/rustc_mir_build/src/lints.rs | 16 |
3 files changed, 139 insertions, 2 deletions
diff --git a/compiler/rustc_mir_build/src/build/expr/stmt.rs b/compiler/rustc_mir_build/src/build/expr/stmt.rs index 2bdeb579a02..88b76c46c90 100644 --- a/compiler/rustc_mir_build/src/build/expr/stmt.rs +++ b/compiler/rustc_mir_build/src/build/expr/stmt.rs @@ -2,7 +2,9 @@ use crate::build::scope::BreakableTarget; use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder}; use rustc_middle::middle::region; use rustc_middle::mir::*; +use rustc_middle::span_bug; use rustc_middle::thir::*; +use rustc_span::source_map::Spanned; use tracing::debug; impl<'a, 'tcx> Builder<'a, 'tcx> { @@ -91,9 +93,42 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { ExprKind::Return { value } => { this.break_scope(block, value, BreakableTarget::Return, source_info) } - // FIXME(explicit_tail_calls): properly lower tail calls here ExprKind::Become { value } => { - this.break_scope(block, Some(value), BreakableTarget::Return, source_info) + let v = &this.thir[value]; + let ExprKind::Scope { value, lint_level, region_scope } = v.kind else { + span_bug!(v.span, "`thir_check_tail_calls` should have disallowed this {v:?}") + }; + + let v = &this.thir[value]; + let ExprKind::Call { ref args, fun, fn_span, .. } = v.kind else { + span_bug!(v.span, "`thir_check_tail_calls` should have disallowed this {v:?}") + }; + + this.in_scope((region_scope, source_info), lint_level, |this| { + let fun = unpack!(block = this.as_local_operand(block, fun)); + let args: Box<[_]> = args + .into_iter() + .copied() + .map(|arg| Spanned { + node: unpack!(block = this.as_local_call_operand(block, arg)), + span: this.thir.exprs[arg].span, + }) + .collect(); + + this.record_operands_moved(&args); + + debug!("expr_into_dest: fn_span={:?}", fn_span); + + unpack!(block = this.break_for_tail_call(block, &args, source_info)); + + this.cfg.terminate( + block, + source_info, + TerminatorKind::TailCall { func: fun, args, fn_span }, + ); + + this.cfg.start_new_block().unit() + }) } _ => { assert!( diff --git a/compiler/rustc_mir_build/src/build/scope.rs b/compiler/rustc_mir_build/src/build/scope.rs index 5b6de39bb2e..948301e2ece 100644 --- a/compiler/rustc_mir_build/src/build/scope.rs +++ b/compiler/rustc_mir_build/src/build/scope.rs @@ -745,6 +745,91 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { self.cfg.terminate(block, source_info, TerminatorKind::UnwindResume); } + /// Sets up the drops for explict tail calls. + /// + /// Unlike other kinds of early exits, tail calls do not go through the drop tree. + /// Instead, all scheduled drops are immediately added to the CFG. + pub(crate) fn break_for_tail_call( + &mut self, + mut block: BasicBlock, + args: &[Spanned<Operand<'tcx>>], + source_info: SourceInfo, + ) -> BlockAnd<()> { + let arg_drops: Vec<_> = args + .iter() + .rev() + .filter_map(|arg| match &arg.node { + Operand::Copy(_) => bug!("copy op in tail call args"), + Operand::Move(place) => { + let local = + place.as_local().unwrap_or_else(|| bug!("projection in tail call args")); + + Some(DropData { source_info, local, kind: DropKind::Value }) + } + Operand::Constant(_) => None, + }) + .collect(); + + let mut unwind_to = self.diverge_cleanup_target( + self.scopes.scopes.iter().rev().nth(1).unwrap().region_scope, + DUMMY_SP, + ); + let unwind_drops = &mut self.scopes.unwind_drops; + + // the innermost scope contains only the destructors for the tail call arguments + // we only want to drop these in case of a panic, so we skip it + for scope in self.scopes.scopes[1..].iter().rev().skip(1) { + // FIXME(explicit_tail_calls) code duplication with `build_scope_drops` + for drop_data in scope.drops.iter().rev() { + let source_info = drop_data.source_info; + let local = drop_data.local; + + match drop_data.kind { + DropKind::Value => { + // `unwind_to` should drop the value that we're about to + // schedule. If dropping this value panics, then we continue + // with the *next* value on the unwind path. + debug_assert_eq!(unwind_drops.drops[unwind_to].data.local, drop_data.local); + debug_assert_eq!(unwind_drops.drops[unwind_to].data.kind, drop_data.kind); + unwind_to = unwind_drops.drops[unwind_to].next; + + let mut unwind_entry_point = unwind_to; + + // the tail call arguments must be dropped if any of these drops panic + for drop in arg_drops.iter().copied() { + unwind_entry_point = unwind_drops.add_drop(drop, unwind_entry_point); + } + + unwind_drops.add_entry_point(block, unwind_entry_point); + + let next = self.cfg.start_new_block(); + self.cfg.terminate( + block, + source_info, + TerminatorKind::Drop { + place: local.into(), + target: next, + unwind: UnwindAction::Continue, + replace: false, + }, + ); + block = next; + } + DropKind::Storage => { + // Only temps and vars need their storage dead. + assert!(local.index() > self.arg_count); + self.cfg.push( + block, + Statement { source_info, kind: StatementKind::StorageDead(local) }, + ); + } + } + } + } + + block.unit() + } + fn leave_top_scope(&mut self, block: BasicBlock) -> BasicBlock { // If we are emitting a `drop` statement, we need to have the cached // diverge cleanup pads ready in case that drop panics. @@ -1523,6 +1608,7 @@ impl<'tcx> DropTreeBuilder<'tcx> for Unwind { | TerminatorKind::UnwindResume | TerminatorKind::UnwindTerminate(_) | TerminatorKind::Return + | TerminatorKind::TailCall { .. } | TerminatorKind::Unreachable | TerminatorKind::Yield { .. } | TerminatorKind::CoroutineDrop diff --git a/compiler/rustc_mir_build/src/lints.rs b/compiler/rustc_mir_build/src/lints.rs index 1c7aa9f9ed0..263e777d03a 100644 --- a/compiler/rustc_mir_build/src/lints.rs +++ b/compiler/rustc_mir_build/src/lints.rs @@ -217,12 +217,28 @@ impl<'mir, 'tcx, C: TerminatorClassifier<'tcx>> TriColorVisitor<BasicBlocks<'tcx | TerminatorKind::FalseUnwind { .. } | TerminatorKind::Goto { .. } | TerminatorKind::SwitchInt { .. } => ControlFlow::Continue(()), + + // Note that tail call terminator technically returns to the caller, + // but for purposes of this lint it makes sense to count it as possibly recursive, + // since it's still a call. + // + // If this'll be repurposed for something else, this might need to be changed. + TerminatorKind::TailCall { .. } => ControlFlow::Continue(()), } } fn node_settled(&mut self, bb: BasicBlock) -> ControlFlow<Self::BreakVal> { // When we examine a node for the last time, remember it if it is a recursive call. let terminator = self.body[bb].terminator(); + + // FIXME(explicit_tail_calls): highlight tail calls as "recursive call site" + // + // We don't want to lint functions that recurse only through tail calls + // (such as `fn g() { become () }`), so just adding `| TailCall { ... }` + // here won't work. + // + // But at the same time we would like to highlight both calls in a function like + // `fn f() { if false { become f() } else { f() } }`, so we need to figure something out. if self.classifier.is_recursive_terminator(self.tcx, self.body, terminator) { self.reachable_recursive_calls.push(terminator.source_info.span); } |