diff options
Diffstat (limited to 'compiler/rustc_codegen_ssa/src/mir/analyze.rs')
| -rw-r--r-- | compiler/rustc_codegen_ssa/src/mir/analyze.rs | 118 |
1 files changed, 63 insertions, 55 deletions
diff --git a/compiler/rustc_codegen_ssa/src/mir/analyze.rs b/compiler/rustc_codegen_ssa/src/mir/analyze.rs index 6d6465dd798..c2c023af090 100644 --- a/compiler/rustc_codegen_ssa/src/mir/analyze.rs +++ b/compiler/rustc_codegen_ssa/src/mir/analyze.rs @@ -1,12 +1,13 @@ //! An analysis to determine which locals require allocas and //! which do not. +use rustc_abi as abi; use rustc_data_structures::graph::dominators::Dominators; use rustc_index::bit_set::DenseBitSet; use rustc_index::{IndexSlice, IndexVec}; use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor}; use rustc_middle::mir::{self, DefLocation, Location, TerminatorKind, traversal}; -use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf}; +use rustc_middle::ty::layout::LayoutOf; use rustc_middle::{bug, span_bug}; use tracing::debug; @@ -99,63 +100,75 @@ impl<'a, 'b, 'tcx, Bx: BuilderMethods<'b, 'tcx>> LocalAnalyzer<'a, 'b, 'tcx, Bx> context: PlaceContext, location: Location, ) { - let cx = self.fx.cx; - - if let Some((place_base, elem)) = place_ref.last_projection() { - let mut base_context = if context.is_mutating_use() { - PlaceContext::MutatingUse(MutatingUseContext::Projection) - } else { - PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection) - }; - - // Allow uses of projections that are ZSTs or from scalar fields. - let is_consume = matches!( - context, - PlaceContext::NonMutatingUse( - NonMutatingUseContext::Copy | NonMutatingUseContext::Move, - ) - ); - if is_consume { - let base_ty = place_base.ty(self.fx.mir, cx.tcx()); - let base_ty = self.fx.monomorphize(base_ty); - - // ZSTs don't require any actual memory access. - let elem_ty = base_ty.projection_ty(cx.tcx(), self.fx.monomorphize(elem)).ty; - let span = self.fx.mir.local_decls[place_ref.local].source_info.span; - if cx.spanned_layout_of(elem_ty, span).is_zst() { - return; + if !place_ref.projection.is_empty() { + const COPY_CONTEXT: PlaceContext = + PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy); + + // `PlaceElem::Index` is the only variant that can mention other `Local`s, + // so check for those up-front before any potential short-circuits. + for elem in place_ref.projection { + if let mir::PlaceElem::Index(index_local) = *elem { + self.visit_local(index_local, COPY_CONTEXT, location); } + } - if let mir::ProjectionElem::Field(..) = elem { - let layout = cx.spanned_layout_of(base_ty.ty, span); - if cx.is_backend_immediate(layout) || cx.is_backend_scalar_pair(layout) { - // Recurse with the same context, instead of `Projection`, - // potentially stopping at non-operand projections, - // which would trigger `not_ssa` on locals. - base_context = context; - } - } + // If our local is already memory, nothing can make it *more* memory + // so we don't need to bother checking the projections further. + if self.locals[place_ref.local] == LocalKind::Memory { + return; } - if let mir::ProjectionElem::Deref = elem { - // Deref projections typically only read the pointer. - base_context = PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy); + if place_ref.is_indirect_first_projection() { + // If this starts with a `Deref`, we only need to record a read of the + // pointer being dereferenced, as all the subsequent projections are + // working on a place which is always supported. (And because we're + // looking at codegen MIR, it can only happen as the first projection.) + self.visit_local(place_ref.local, COPY_CONTEXT, location); + return; } - self.process_place(&place_base, base_context, location); - // HACK(eddyb) this emulates the old `visit_projection_elem`, this - // entire `visit_place`-like `process_place` method should be rewritten, - // now that we have moved to the "slice of projections" representation. - if let mir::ProjectionElem::Index(local) = elem { - self.visit_local( - local, - PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy), - location, - ); + if context.is_mutating_use() { + // If it's a mutating use it doesn't matter what the projections are, + // if there are *any* then we need a place to write. (For example, + // `_1 = Foo()` works in SSA but `_2.0 = Foo()` does not.) + let mut_projection = PlaceContext::MutatingUse(MutatingUseContext::Projection); + self.visit_local(place_ref.local, mut_projection, location); + return; } - } else { - self.visit_local(place_ref.local, context, location); + + // Scan through to ensure the only projections are those which + // `FunctionCx::maybe_codegen_consume_direct` can handle. + let base_ty = self.fx.monomorphized_place_ty(mir::PlaceRef::from(place_ref.local)); + let mut layout = self.fx.cx.layout_of(base_ty); + for elem in place_ref.projection { + layout = match *elem { + mir::PlaceElem::Field(fidx, ..) => layout.field(self.fx.cx, fidx.as_usize()), + mir::PlaceElem::Downcast(_, vidx) + if let abi::Variants::Single { index: single_variant } = + layout.variants + && vidx == single_variant => + { + layout.for_variant(self.fx.cx, vidx) + } + mir::PlaceElem::Subtype(subtype_ty) => { + let subtype_ty = self.fx.monomorphize(subtype_ty); + self.fx.cx.layout_of(subtype_ty) + } + _ => { + self.locals[place_ref.local] = LocalKind::Memory; + return; + } + } + } + debug_assert!( + !self.fx.cx.is_backend_ref(layout), + "Post-projection {place_ref:?} layout should be non-Ref, but it's {layout:?}", + ); } + + // Even with supported projections, we still need to have `visit_local` + // check for things that can't be done in SSA (like `SharedBorrow`). + self.visit_local(place_ref.local, context, location); } } @@ -170,11 +183,6 @@ impl<'a, 'b, 'tcx, Bx: BuilderMethods<'b, 'tcx>> Visitor<'tcx> for LocalAnalyzer if let Some(local) = place.as_local() { self.define(local, DefLocation::Assignment(location)); - if self.locals[local] != LocalKind::Memory { - if !self.fx.rvalue_creates_operand(rvalue) { - self.locals[local] = LocalKind::Memory; - } - } } else { self.visit_place(place, PlaceContext::MutatingUse(MutatingUseContext::Store), location); } |