diff options
Diffstat (limited to 'compiler/rustc_mir_transform/src/const_prop.rs')
| -rw-r--r-- | compiler/rustc_mir_transform/src/const_prop.rs | 127 |
1 files changed, 66 insertions, 61 deletions
diff --git a/compiler/rustc_mir_transform/src/const_prop.rs b/compiler/rustc_mir_transform/src/const_prop.rs index fbc0a767f..7a2a15a84 100644 --- a/compiler/rustc_mir_transform/src/const_prop.rs +++ b/compiler/rustc_mir_transform/src/const_prop.rs @@ -28,7 +28,7 @@ use crate::MirPass; use rustc_const_eval::interpret::{ self, compile_time_machine, AllocId, ConstAllocation, ConstValue, CtfeValidationMode, Frame, ImmTy, Immediate, InterpCx, InterpResult, LocalState, LocalValue, MemoryKind, OpTy, PlaceTy, - Pointer, Scalar, ScalarMaybeUninit, StackPopCleanup, StackPopUnwind, + Pointer, Scalar, StackPopCleanup, StackPopUnwind, }; /// The maximum number of bytes that we'll allocate space for a local or the return value. @@ -131,7 +131,7 @@ impl<'tcx> MirPass<'tcx> for ConstProp { let dummy_body = &Body::new( body.source, - body.basic_blocks().clone(), + (*body.basic_blocks).clone(), body.source_scopes.clone(), body.local_decls.clone(), Default::default(), @@ -183,6 +183,18 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine<'mir, 'tcx> type MemoryKind = !; + #[inline(always)] + fn enforce_alignment(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool { + // We do not check for alignment to avoid having to carry an `Align` + // in `ConstValue::ByRef`. + false + } + + #[inline(always)] + fn enforce_validity(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool { + false // for now, we don't enforce validity + } + fn load_mir( _ecx: &InterpCx<'mir, 'tcx, Self>, _instance: ty::InstanceDef<'tcx>, @@ -231,24 +243,6 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine<'mir, 'tcx> throw_machine_stop_str!("pointer arithmetic or comparisons aren't supported in ConstProp") } - fn access_local<'a>( - frame: &'a Frame<'mir, 'tcx, Self::Provenance, Self::FrameExtra>, - local: Local, - ) -> InterpResult<'tcx, &'a interpret::Operand<Self::Provenance>> { - let l = &frame.locals[local]; - - if matches!( - l.value, - LocalValue::Live(interpret::Operand::Immediate(interpret::Immediate::Uninit)) - ) { - // For us "uninit" means "we don't know its value, might be initiailized or not". - // So stop here. - throw_machine_stop_str!("tried to access alocal with unknown value ") - } - - l.access() - } - fn access_local_mut<'a>( ecx: &'a mut InterpCx<'mir, 'tcx, Self>, frame: usize, @@ -419,7 +413,13 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { fn get_const(&self, place: Place<'tcx>) -> Option<OpTy<'tcx>> { let op = match self.ecx.eval_place_to_op(place, None) { - Ok(op) => op, + Ok(op) => { + if matches!(*op, interpret::Operand::Immediate(Immediate::Uninit)) { + // Make sure nobody accidentally uses this value. + return None; + } + op + } Err(e) => { trace!("get_const failed: {}", e); return None; @@ -428,7 +428,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { // Try to read the local as an immediate so that if it is representable as a scalar, we can // handle it as such, but otherwise, just return the value as is. - Some(match self.ecx.read_immediate_raw(&op, /*force*/ false) { + Some(match self.ecx.read_immediate_raw(&op) { Ok(Ok(imm)) => imm.into(), _ => op, }) @@ -520,8 +520,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { let left_ty = left.ty(self.local_decls, self.tcx); let left_size = self.ecx.layout_of(left_ty).ok()?.size; let right_size = r.layout.size; - let r_bits = r.to_scalar().ok(); - let r_bits = r_bits.and_then(|r| r.to_bits(right_size).ok()); + let r_bits = r.to_scalar().to_bits(right_size).ok(); if r_bits.map_or(false, |b| b >= left_size.bits() as u128) { return None; } @@ -550,7 +549,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { // and use it to do const-prop here and everywhere else // where it makes sense. if let interpret::Operand::Immediate(interpret::Immediate::Scalar( - ScalarMaybeUninit::Scalar(scalar), + scalar, )) = *value { *operand = self.operand_from_scalar( @@ -632,6 +631,14 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { if rvalue.needs_subst() { return None; } + if !rvalue + .ty(&self.ecx.frame().body.local_decls, *self.ecx.tcx) + .is_sized(self.ecx.tcx, self.param_env) + { + // the interpreter doesn't support unsized locals (only unsized arguments), + // but rustc does (in a kinda broken way), so we have to skip them here + return None; + } if self.tcx.sess.mir_opt_level() >= 4 { self.eval_rvalue_with_identities(rvalue, place) @@ -649,21 +656,23 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { self.use_ecx(|this| match rvalue { Rvalue::BinaryOp(op, box (left, right)) | Rvalue::CheckedBinaryOp(op, box (left, right)) => { - let l = this.ecx.eval_operand(left, None); - let r = this.ecx.eval_operand(right, None); + let l = this.ecx.eval_operand(left, None).and_then(|x| this.ecx.read_immediate(&x)); + let r = + this.ecx.eval_operand(right, None).and_then(|x| this.ecx.read_immediate(&x)); let const_arg = match (l, r) { - (Ok(ref x), Err(_)) | (Err(_), Ok(ref x)) => this.ecx.read_immediate(x)?, - (Err(e), Err(_)) => return Err(e), - (Ok(_), Ok(_)) => return this.ecx.eval_rvalue_into_place(rvalue, place), + (Ok(x), Err(_)) | (Err(_), Ok(x)) => x, // exactly one side is known + (Err(e), Err(_)) => return Err(e), // neither side is known + (Ok(_), Ok(_)) => return this.ecx.eval_rvalue_into_place(rvalue, place), // both sides are known }; if !matches!(const_arg.layout.abi, abi::Abi::Scalar(..)) { // We cannot handle Scalar Pair stuff. - return this.ecx.eval_rvalue_into_place(rvalue, place); + // No point in calling `eval_rvalue_into_place`, since only one side is known + throw_machine_stop_str!("cannot optimize this") } - let arg_value = const_arg.to_scalar()?.to_bits(const_arg.layout.size)?; + let arg_value = const_arg.to_scalar().to_bits(const_arg.layout.size)?; let dest = this.ecx.eval_place(place)?; match op { @@ -677,7 +686,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { BinOp::Mul if const_arg.layout.ty.is_integral() && arg_value == 0 => { if let Rvalue::CheckedBinaryOp(_, _) = rvalue { let val = Immediate::ScalarPair( - const_arg.to_scalar()?.into(), + const_arg.to_scalar().into(), Scalar::from_bool(false).into(), ); this.ecx.write_immediate(val, &dest) @@ -685,7 +694,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { this.ecx.write_immediate(*const_arg, &dest) } } - _ => this.ecx.eval_rvalue_into_place(rvalue, place), + _ => throw_machine_stop_str!("cannot optimize this"), } } _ => this.ecx.eval_rvalue_into_place(rvalue, place), @@ -731,21 +740,18 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { } // FIXME> figure out what to do when read_immediate_raw fails - let imm = self.use_ecx(|this| this.ecx.read_immediate_raw(value, /*force*/ false)); + let imm = self.use_ecx(|this| this.ecx.read_immediate_raw(value)); if let Some(Ok(imm)) = imm { match *imm { - interpret::Immediate::Scalar(ScalarMaybeUninit::Scalar(scalar)) => { + interpret::Immediate::Scalar(scalar) => { *rval = Rvalue::Use(self.operand_from_scalar( scalar, value.layout.ty, source_info.span, )); } - Immediate::ScalarPair( - ScalarMaybeUninit::Scalar(_), - ScalarMaybeUninit::Scalar(_), - ) => { + Immediate::ScalarPair(..) => { // Found a value represented as a pair. For now only do const-prop if the type // of `rvalue` is also a tuple with two scalars. // FIXME: enable the general case stated above ^. @@ -800,13 +806,10 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { } match **op { - interpret::Operand::Immediate(Immediate::Scalar(ScalarMaybeUninit::Scalar(s))) => { - s.try_to_int().is_ok() + interpret::Operand::Immediate(Immediate::Scalar(s)) => s.try_to_int().is_ok(), + interpret::Operand::Immediate(Immediate::ScalarPair(l, r)) => { + l.try_to_int().is_ok() && r.try_to_int().is_ok() } - interpret::Operand::Immediate(Immediate::ScalarPair( - ScalarMaybeUninit::Scalar(l), - ScalarMaybeUninit::Scalar(r), - )) => l.try_to_int().is_ok() && r.try_to_int().is_ok(), _ => false, } } @@ -951,7 +954,7 @@ impl<'tcx> MutVisitor<'tcx> for ConstPropagator<'_, 'tcx> { } fn visit_body(&mut self, body: &mut Body<'tcx>) { - for (bb, data) in body.basic_blocks_mut().iter_enumerated_mut() { + for (bb, data) in body.basic_blocks.as_mut_preserves_cfg().iter_enumerated_mut() { self.visit_basic_block_data(bb, data); } } @@ -1063,26 +1066,28 @@ impl<'tcx> MutVisitor<'tcx> for ConstPropagator<'_, 'tcx> { let source_info = terminator.source_info; self.source_info = Some(source_info); self.super_terminator(terminator, location); + // Do NOT early return in this function, it does some crucial fixup of the state at the end! match &mut terminator.kind { TerminatorKind::Assert { expected, ref mut cond, .. } => { if let Some(ref value) = self.eval_operand(&cond) { trace!("assertion on {:?} should be {:?}", value, expected); - let expected = ScalarMaybeUninit::from(Scalar::from_bool(*expected)); - let value_const = self.ecx.read_scalar(&value).unwrap(); - if expected != value_const { - // Poison all places this operand references so that further code - // doesn't use the invalid value - match cond { - Operand::Move(ref place) | Operand::Copy(ref place) => { - Self::remove_const(&mut self.ecx, place.local); + let expected = Scalar::from_bool(*expected); + // FIXME should be used use_ecx rather than a local match... but we have + // quite a few of these read_scalar/read_immediate that need fixing. + if let Ok(value_const) = self.ecx.read_scalar(&value) { + if expected != value_const { + // Poison all places this operand references so that further code + // doesn't use the invalid value + match cond { + Operand::Move(ref place) | Operand::Copy(ref place) => { + Self::remove_const(&mut self.ecx, place.local); + } + Operand::Constant(_) => {} } - Operand::Constant(_) => {} - } - } else { - if self.should_const_prop(value) { - if let ScalarMaybeUninit::Scalar(scalar) = value_const { + } else { + if self.should_const_prop(value) { *cond = self.operand_from_scalar( - scalar, + value_const, self.tcx.types.bool, source_info.span, ); |