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interpret: remove LocalValue::Unallocated, add Operand::Uninit

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Operand::Uninit is an *allocated* operand that is fully uninitialized.
This lets us lazily allocate the actual backing store of *all* locals (no matter their ABI).

I also reordered things in pop_stack_frame at the same time.
I should probably have made that a separate commit...
This commit is contained in:
Ralf Jung
2022-07-02 16:24:42 -04:00
parent 049308cf8b
commit 8ef0caa23c
8 changed files with 179 additions and 175 deletions
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33
compiler/rustc_mir_transform/src/const_prop_lint.rs
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@@ -31,8 +31,8 @@ use crate::MirLint;
use rustc_const_eval::const_eval::ConstEvalErr;
use rustc_const_eval::interpret::{
self, compile_time_machine, AllocId, ConstAllocation, Frame, ImmTy, InterpCx, InterpResult,
LocalState, LocalValue, MemPlace, MemoryKind, OpTy, Operand as InterpOperand, PlaceTy, Pointer,
Scalar, ScalarMaybeUninit, StackPopCleanup, StackPopUnwind,
LocalState, LocalValue, MemoryKind, OpTy, PlaceTy, Pointer, Scalar, ScalarMaybeUninit,
StackPopCleanup, StackPopUnwind,
};
/// The maximum number of bytes that we'll allocate space for a local or the return value.
@@ -229,15 +229,19 @@ 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(
_ecx: &InterpCx<'mir, 'tcx, Self>,
frame: &Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>,
fn access_local<'a>(
frame: &'a Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>,
local: Local,
) -> InterpResult<'tcx, InterpOperand<Self::PointerTag>> {
) -> InterpResult<'tcx, &'a interpret::Operand<Self::PointerTag>> {
let l = &frame.locals[local];
if l.value == LocalValue::Unallocated {
throw_machine_stop_str!("tried to access an uninitialized 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 a local with unknown value")
}
l.access()
@@ -247,8 +251,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine<'mir, 'tcx>
ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
frame: usize,
local: Local,
) -> InterpResult<'tcx, Result<&'a mut LocalValue<Self::PointerTag>, MemPlace<Self::PointerTag>>>
{
) -> InterpResult<'tcx, &'a mut interpret::Operand<Self::PointerTag>> {
if ecx.machine.can_const_prop[local] == ConstPropMode::NoPropagation {
throw_machine_stop_str!("tried to write to a local that is marked as not propagatable")
}
@@ -430,8 +433,10 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
/// Remove `local` from the pool of `Locals`. Allows writing to them,
/// but not reading from them anymore.
fn remove_const(ecx: &mut InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>, local: Local) {
ecx.frame_mut().locals[local] =
LocalState { value: LocalValue::Unallocated, layout: Cell::new(None) };
ecx.frame_mut().locals[local] = LocalState {
value: LocalValue::Live(interpret::Operand::Immediate(interpret::Immediate::Uninit)),
layout: Cell::new(None),
};
}
fn lint_root(&self, source_info: SourceInfo) -> Option<HirId> {
@@ -915,7 +920,9 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
let frame = self.ecx.frame_mut();
frame.locals[local].value =
if let StatementKind::StorageLive(_) = statement.kind {
LocalValue::Unallocated
LocalValue::Live(interpret::Operand::Immediate(
interpret::Immediate::Uninit,
))
} else {
LocalValue::Dead
};