diff options
Diffstat (limited to 'compiler/rustc_mir_transform/src')
| -rw-r--r-- | compiler/rustc_mir_transform/src/abort_unwinding_calls.rs | 37 | ||||
| -rw-r--r-- | compiler/rustc_mir_transform/src/patch.rs | 30 | ||||
| -rw-r--r-- | compiler/rustc_mir_transform/src/simplify_branches.rs | 19 |
3 files changed, 66 insertions, 20 deletions
diff --git a/compiler/rustc_mir_transform/src/abort_unwinding_calls.rs b/compiler/rustc_mir_transform/src/abort_unwinding_calls.rs index 5bd6fdcf485..35a21a2a834 100644 --- a/compiler/rustc_mir_transform/src/abort_unwinding_calls.rs +++ b/compiler/rustc_mir_transform/src/abort_unwinding_calls.rs @@ -3,6 +3,7 @@ use rustc_ast::InlineAsmOptions; use rustc_middle::mir::*; use rustc_middle::span_bug; use rustc_middle::ty::{self, TyCtxt, layout}; +use rustc_span::sym; use rustc_target::spec::PanicStrategy; /// A pass that runs which is targeted at ensuring that codegen guarantees about @@ -33,6 +34,19 @@ impl<'tcx> crate::MirPass<'tcx> for AbortUnwindingCalls { return; } + // Represent whether this compilation target fundamentally doesn't + // support unwinding at all at an ABI level. If this the target has no + // support for unwinding then cleanup actions, for example, are all + // unnecessary and can be considered unreachable. + // + // Currently this is only true for wasm targets on panic=abort when the + // `exception-handling` target feature is disabled. In such a + // configuration it's illegal to emit exception-related instructions so + // it's not possible to unwind. + let target_supports_unwinding = !(tcx.sess.target.is_like_wasm + && tcx.sess.panic_strategy() == PanicStrategy::Abort + && !tcx.asm_target_features(def_id).contains(&sym::exception_handling)); + // Here we test for this function itself whether its ABI allows // unwinding or not. let body_ty = tcx.type_of(def_id).skip_binder(); @@ -54,12 +68,18 @@ impl<'tcx> crate::MirPass<'tcx> for AbortUnwindingCalls { let Some(terminator) = &mut block.terminator else { continue }; let span = terminator.source_info.span; - // If we see an `UnwindResume` terminator inside a function that cannot unwind, we need - // to replace it with `UnwindTerminate`. - if let TerminatorKind::UnwindResume = &terminator.kind - && !body_can_unwind - { - terminator.kind = TerminatorKind::UnwindTerminate(UnwindTerminateReason::Abi); + // If we see an `UnwindResume` terminator inside a function then: + // + // * If the target doesn't support unwinding at all, then this is an + // unreachable block. + // * If the body cannot unwind, we need to replace it with + // `UnwindTerminate`. + if let TerminatorKind::UnwindResume = &terminator.kind { + if !target_supports_unwinding { + terminator.kind = TerminatorKind::Unreachable; + } else if !body_can_unwind { + terminator.kind = TerminatorKind::UnwindTerminate(UnwindTerminateReason::Abi); + } } if block.is_cleanup { @@ -93,8 +113,9 @@ impl<'tcx> crate::MirPass<'tcx> for AbortUnwindingCalls { _ => continue, }; - if !call_can_unwind { - // If this function call can't unwind, then there's no need for it + if !call_can_unwind || !target_supports_unwinding { + // If this function call can't unwind, or if the target doesn't + // support unwinding at all, then there's no need for it // to have a landing pad. This means that we can remove any cleanup // registered for it (and turn it into `UnwindAction::Unreachable`). let cleanup = block.terminator_mut().unwind_mut().unwrap(); diff --git a/compiler/rustc_mir_transform/src/patch.rs b/compiler/rustc_mir_transform/src/patch.rs index d831ab50b1a..cc8ea76011b 100644 --- a/compiler/rustc_mir_transform/src/patch.rs +++ b/compiler/rustc_mir_transform/src/patch.rs @@ -11,6 +11,8 @@ use tracing::debug; /// once with `apply`. This is useful for MIR transformation passes. pub(crate) struct MirPatch<'tcx> { term_patch_map: FxHashMap<BasicBlock, TerminatorKind<'tcx>>, + /// Set of statements that should be replaced by `Nop`. + nop_statements: Vec<Location>, new_blocks: Vec<BasicBlockData<'tcx>>, new_statements: Vec<(Location, StatementKind<'tcx>)>, new_locals: Vec<LocalDecl<'tcx>>, @@ -33,6 +35,7 @@ impl<'tcx> MirPatch<'tcx> { pub(crate) fn new(body: &Body<'tcx>) -> Self { let mut result = MirPatch { term_patch_map: Default::default(), + nop_statements: vec![], new_blocks: vec![], new_statements: vec![], new_locals: vec![], @@ -212,6 +215,15 @@ impl<'tcx> MirPatch<'tcx> { self.term_patch_map.insert(block, new); } + /// Mark given statement to be replaced by a `Nop`. + /// + /// This method only works on statements from the initial body, and cannot be used to remove + /// statements from `add_statement` or `add_assign`. + #[tracing::instrument(level = "debug", skip(self))] + pub(crate) fn nop_statement(&mut self, loc: Location) { + self.nop_statements.push(loc); + } + /// Queues the insertion of a statement at a given location. The statement /// currently at that location, and all statements that follow, are shifted /// down. If multiple statements are queued for addition at the same @@ -257,11 +269,8 @@ impl<'tcx> MirPatch<'tcx> { bbs.extend(self.new_blocks); body.local_decls.extend(self.new_locals); - // The order in which we patch terminators does not change the result. - #[allow(rustc::potential_query_instability)] - for (src, patch) in self.term_patch_map { - debug!("MirPatch: patching block {:?}", src); - bbs[src].terminator_mut().kind = patch; + for loc in self.nop_statements { + bbs[loc.block].statements[loc.statement_index].make_nop(); } let mut new_statements = self.new_statements; @@ -285,6 +294,17 @@ impl<'tcx> MirPatch<'tcx> { .insert(loc.statement_index, Statement::new(source_info, stmt)); delta += 1; } + + // The order in which we patch terminators does not change the result. + #[allow(rustc::potential_query_instability)] + for (src, patch) in self.term_patch_map { + debug!("MirPatch: patching block {:?}", src); + let bb = &mut bbs[src]; + if let TerminatorKind::Unreachable = patch { + bb.statements.clear(); + } + bb.terminator_mut().kind = patch; + } } fn source_info_for_index(data: &BasicBlockData<'_>, loc: Location) -> SourceInfo { diff --git a/compiler/rustc_mir_transform/src/simplify_branches.rs b/compiler/rustc_mir_transform/src/simplify_branches.rs index 886f4d6e509..ed94a058ec6 100644 --- a/compiler/rustc_mir_transform/src/simplify_branches.rs +++ b/compiler/rustc_mir_transform/src/simplify_branches.rs @@ -2,6 +2,8 @@ use rustc_middle::mir::*; use rustc_middle::ty::TyCtxt; use tracing::trace; +use crate::patch::MirPatch; + pub(super) enum SimplifyConstCondition { AfterConstProp, Final, @@ -19,8 +21,10 @@ impl<'tcx> crate::MirPass<'tcx> for SimplifyConstCondition { fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { trace!("Running SimplifyConstCondition on {:?}", body.source); let typing_env = body.typing_env(tcx); - 'blocks: for block in body.basic_blocks_mut() { - for stmt in block.statements.iter_mut() { + let mut patch = MirPatch::new(body); + + 'blocks: for (bb, block) in body.basic_blocks.iter_enumerated() { + for (statement_index, stmt) in block.statements.iter().enumerate() { // Simplify `assume` of a known value: either a NOP or unreachable. if let StatementKind::Intrinsic(box ref intrinsic) = stmt.kind && let NonDivergingIntrinsic::Assume(discr) = intrinsic @@ -28,17 +32,16 @@ impl<'tcx> crate::MirPass<'tcx> for SimplifyConstCondition { && let Some(constant) = c.const_.try_eval_bool(tcx, typing_env) { if constant { - stmt.make_nop(); + patch.nop_statement(Location { block: bb, statement_index }); } else { - block.statements.clear(); - block.terminator_mut().kind = TerminatorKind::Unreachable; + patch.patch_terminator(bb, TerminatorKind::Unreachable); continue 'blocks; } } } - let terminator = block.terminator_mut(); - terminator.kind = match terminator.kind { + let terminator = block.terminator(); + let terminator = match terminator.kind { TerminatorKind::SwitchInt { discr: Operand::Constant(ref c), ref targets, .. } => { @@ -58,7 +61,9 @@ impl<'tcx> crate::MirPass<'tcx> for SimplifyConstCondition { }, _ => continue, }; + patch.patch_terminator(bb, terminator); } + patch.apply(body); } fn is_required(&self) -> bool { |