diff options
Diffstat (limited to 'compiler/rustc_mir_transform/src/instsimplify.rs')
| -rw-r--r-- | compiler/rustc_mir_transform/src/instsimplify.rs | 305 |
1 files changed, 305 insertions, 0 deletions
diff --git a/compiler/rustc_mir_transform/src/instsimplify.rs b/compiler/rustc_mir_transform/src/instsimplify.rs new file mode 100644 index 000000000..e4dc61762 --- /dev/null +++ b/compiler/rustc_mir_transform/src/instsimplify.rs @@ -0,0 +1,305 @@ +//! Performs various peephole optimizations. + +use crate::simplify::simplify_duplicate_switch_targets; +use crate::MirPass; +use rustc_hir::Mutability; +use rustc_middle::mir::*; +use rustc_middle::ty::layout::ValidityRequirement; +use rustc_middle::ty::{self, ParamEnv, SubstsRef, Ty, TyCtxt}; +use rustc_span::symbol::Symbol; +use rustc_target::abi::FieldIdx; + +pub struct InstSimplify; + +impl<'tcx> MirPass<'tcx> for InstSimplify { + fn is_enabled(&self, sess: &rustc_session::Session) -> bool { + sess.mir_opt_level() > 0 + } + + fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { + let ctx = InstSimplifyContext { + tcx, + local_decls: &body.local_decls, + param_env: tcx.param_env_reveal_all_normalized(body.source.def_id()), + }; + for block in body.basic_blocks.as_mut() { + for statement in block.statements.iter_mut() { + match statement.kind { + StatementKind::Assign(box (_place, ref mut rvalue)) => { + ctx.simplify_bool_cmp(&statement.source_info, rvalue); + ctx.simplify_ref_deref(&statement.source_info, rvalue); + ctx.simplify_len(&statement.source_info, rvalue); + ctx.simplify_cast(&statement.source_info, rvalue); + } + _ => {} + } + } + + ctx.simplify_primitive_clone( + &mut block.terminator.as_mut().unwrap(), + &mut block.statements, + ); + ctx.simplify_intrinsic_assert( + &mut block.terminator.as_mut().unwrap(), + &mut block.statements, + ); + simplify_duplicate_switch_targets(block.terminator.as_mut().unwrap()); + } + } +} + +struct InstSimplifyContext<'tcx, 'a> { + tcx: TyCtxt<'tcx>, + local_decls: &'a LocalDecls<'tcx>, + param_env: ParamEnv<'tcx>, +} + +impl<'tcx> InstSimplifyContext<'tcx, '_> { + fn should_simplify(&self, source_info: &SourceInfo, rvalue: &Rvalue<'tcx>) -> bool { + self.tcx.consider_optimizing(|| { + format!("InstSimplify - Rvalue: {:?} SourceInfo: {:?}", rvalue, source_info) + }) + } + + /// Transform boolean comparisons into logical operations. + fn simplify_bool_cmp(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) { + match rvalue { + Rvalue::BinaryOp(op @ (BinOp::Eq | BinOp::Ne), box (a, b)) => { + let new = match (op, self.try_eval_bool(a), self.try_eval_bool(b)) { + // Transform "Eq(a, true)" ==> "a" + (BinOp::Eq, _, Some(true)) => Some(Rvalue::Use(a.clone())), + + // Transform "Ne(a, false)" ==> "a" + (BinOp::Ne, _, Some(false)) => Some(Rvalue::Use(a.clone())), + + // Transform "Eq(true, b)" ==> "b" + (BinOp::Eq, Some(true), _) => Some(Rvalue::Use(b.clone())), + + // Transform "Ne(false, b)" ==> "b" + (BinOp::Ne, Some(false), _) => Some(Rvalue::Use(b.clone())), + + // Transform "Eq(false, b)" ==> "Not(b)" + (BinOp::Eq, Some(false), _) => Some(Rvalue::UnaryOp(UnOp::Not, b.clone())), + + // Transform "Ne(true, b)" ==> "Not(b)" + (BinOp::Ne, Some(true), _) => Some(Rvalue::UnaryOp(UnOp::Not, b.clone())), + + // Transform "Eq(a, false)" ==> "Not(a)" + (BinOp::Eq, _, Some(false)) => Some(Rvalue::UnaryOp(UnOp::Not, a.clone())), + + // Transform "Ne(a, true)" ==> "Not(a)" + (BinOp::Ne, _, Some(true)) => Some(Rvalue::UnaryOp(UnOp::Not, a.clone())), + + _ => None, + }; + + if let Some(new) = new && self.should_simplify(source_info, rvalue) { + *rvalue = new; + } + } + + _ => {} + } + } + + fn try_eval_bool(&self, a: &Operand<'_>) -> Option<bool> { + let a = a.constant()?; + if a.literal.ty().is_bool() { a.literal.try_to_bool() } else { None } + } + + /// Transform "&(*a)" ==> "a". + fn simplify_ref_deref(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) { + if let Rvalue::Ref(_, _, place) = rvalue { + if let Some((base, ProjectionElem::Deref)) = place.as_ref().last_projection() { + if rvalue.ty(self.local_decls, self.tcx) != base.ty(self.local_decls, self.tcx).ty { + return; + } + + if !self.should_simplify(source_info, rvalue) { + return; + } + + *rvalue = Rvalue::Use(Operand::Copy(Place { + local: base.local, + projection: self.tcx.mk_place_elems(base.projection), + })); + } + } + } + + /// Transform "Len([_; N])" ==> "N". + fn simplify_len(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) { + if let Rvalue::Len(ref place) = *rvalue { + let place_ty = place.ty(self.local_decls, self.tcx).ty; + if let ty::Array(_, len) = *place_ty.kind() { + if !self.should_simplify(source_info, rvalue) { + return; + } + + let literal = ConstantKind::from_const(len, self.tcx); + let constant = Constant { span: source_info.span, literal, user_ty: None }; + *rvalue = Rvalue::Use(Operand::Constant(Box::new(constant))); + } + } + } + + fn simplify_cast(&self, _source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) { + if let Rvalue::Cast(kind, operand, cast_ty) = rvalue { + let operand_ty = operand.ty(self.local_decls, self.tcx); + if operand_ty == *cast_ty { + *rvalue = Rvalue::Use(operand.clone()); + } else if *kind == CastKind::Transmute { + // Transmuting an integer to another integer is just a signedness cast + if let (ty::Int(int), ty::Uint(uint)) | (ty::Uint(uint), ty::Int(int)) = (operand_ty.kind(), cast_ty.kind()) + && int.bit_width() == uint.bit_width() + { + // The width check isn't strictly necessary, as different widths + // are UB and thus we'd be allowed to turn it into a cast anyway. + // But let's keep the UB around for codegen to exploit later. + // (If `CastKind::Transmute` ever becomes *not* UB for mismatched sizes, + // then the width check is necessary for big-endian correctness.) + *kind = CastKind::IntToInt; + return; + } + + // Transmuting a transparent struct/union to a field's type is a projection + if let ty::Adt(adt_def, substs) = operand_ty.kind() + && adt_def.repr().transparent() + && (adt_def.is_struct() || adt_def.is_union()) + && let Some(place) = operand.place() + { + let variant = adt_def.non_enum_variant(); + for (i, field) in variant.fields.iter().enumerate() { + let field_ty = field.ty(self.tcx, substs); + if field_ty == *cast_ty { + let place = place.project_deeper(&[ProjectionElem::Field(FieldIdx::from_usize(i), *cast_ty)], self.tcx); + let operand = if operand.is_move() { Operand::Move(place) } else { Operand::Copy(place) }; + *rvalue = Rvalue::Use(operand); + return; + } + } + } + } + } + } + + fn simplify_primitive_clone( + &self, + terminator: &mut Terminator<'tcx>, + statements: &mut Vec<Statement<'tcx>>, + ) { + let TerminatorKind::Call { func, args, destination, target, .. } = &mut terminator.kind + else { return }; + + // It's definitely not a clone if there are multiple arguments + if args.len() != 1 { + return; + } + + let Some(destination_block) = *target + else { return }; + + // Only bother looking more if it's easy to know what we're calling + let Some((fn_def_id, fn_substs)) = func.const_fn_def() + else { return }; + + // Clone needs one subst, so we can cheaply rule out other stuff + if fn_substs.len() != 1 { + return; + } + + // These types are easily available from locals, so check that before + // doing DefId lookups to figure out what we're actually calling. + let arg_ty = args[0].ty(self.local_decls, self.tcx); + + let ty::Ref(_region, inner_ty, Mutability::Not) = *arg_ty.kind() + else { return }; + + if !inner_ty.is_trivially_pure_clone_copy() { + return; + } + + let trait_def_id = self.tcx.trait_of_item(fn_def_id); + if trait_def_id.is_none() || trait_def_id != self.tcx.lang_items().clone_trait() { + return; + } + + if !self.tcx.consider_optimizing(|| { + format!( + "InstSimplify - Call: {:?} SourceInfo: {:?}", + (fn_def_id, fn_substs), + terminator.source_info + ) + }) { + return; + } + + let Some(arg_place) = args.pop().unwrap().place() + else { return }; + + statements.push(Statement { + source_info: terminator.source_info, + kind: StatementKind::Assign(Box::new(( + *destination, + Rvalue::Use(Operand::Copy( + arg_place.project_deeper(&[ProjectionElem::Deref], self.tcx), + )), + ))), + }); + terminator.kind = TerminatorKind::Goto { target: destination_block }; + } + + fn simplify_intrinsic_assert( + &self, + terminator: &mut Terminator<'tcx>, + _statements: &mut Vec<Statement<'tcx>>, + ) { + let TerminatorKind::Call { func, target, .. } = &mut terminator.kind else { return; }; + let Some(target_block) = target else { return; }; + let func_ty = func.ty(self.local_decls, self.tcx); + let Some((intrinsic_name, substs)) = resolve_rust_intrinsic(self.tcx, func_ty) else { + return; + }; + // The intrinsics we are interested in have one generic parameter + if substs.is_empty() { + return; + } + let ty = substs.type_at(0); + + let known_is_valid = intrinsic_assert_panics(self.tcx, self.param_env, ty, intrinsic_name); + match known_is_valid { + // We don't know the layout or it's not validity assertion at all, don't touch it + None => {} + Some(true) => { + // If we know the assert panics, indicate to later opts that the call diverges + *target = None; + } + Some(false) => { + // If we know the assert does not panic, turn the call into a Goto + terminator.kind = TerminatorKind::Goto { target: *target_block }; + } + } + } +} + +fn intrinsic_assert_panics<'tcx>( + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + ty: Ty<'tcx>, + intrinsic_name: Symbol, +) -> Option<bool> { + let requirement = ValidityRequirement::from_intrinsic(intrinsic_name)?; + Some(!tcx.check_validity_requirement((requirement, param_env.and(ty))).ok()?) +} + +fn resolve_rust_intrinsic<'tcx>( + tcx: TyCtxt<'tcx>, + func_ty: Ty<'tcx>, +) -> Option<(Symbol, SubstsRef<'tcx>)> { + if let ty::FnDef(def_id, substs) = *func_ty.kind() { + if tcx.is_intrinsic(def_id) { + return Some((tcx.item_name(def_id), substs)); + } + } + None +} |