Const prop doesn't need a stack anymore

Author: oli-obk

compiler/rustc_mir_transform/src/const_prop.rs

@@ -49,24 +49,18 @@ pub(crate) macro throw_machine_stop_str($($tt:tt)*) {{
     throw_machine_stop!(Zst)
 }}
 
-pub(crate) struct ConstPropMachine<'mir, 'tcx> {
-    /// The virtual call stack.
-    stack: Vec<Frame<'mir, 'tcx>>,
+pub(crate) struct ConstPropMachine {
     pub written_only_inside_own_block_locals: FxHashSet<Local>,
     pub can_const_prop: IndexVec<Local, ConstPropMode>,
 }
 
-impl ConstPropMachine<'_, '_> {
+impl ConstPropMachine {
     pub fn new(can_const_prop: IndexVec<Local, ConstPropMode>) -> Self {
-        Self {
-            stack: Vec::new(),
-            written_only_inside_own_block_locals: Default::default(),
-            can_const_prop,
-        }
+        Self { written_only_inside_own_block_locals: Default::default(), can_const_prop }
     }
 }
 
-impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine<'mir, 'tcx> {
+impl<'mir, 'tcx: 'mir> interpret::Machine<'mir, 'tcx> for ConstPropMachine {
     compile_time_machine!(<'mir, 'tcx>);
 
     const PANIC_ON_ALLOC_FAIL: bool = true; // all allocations are small (see `MAX_ALLOC_LIMIT`)
@@ -192,16 +186,16 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine<'mir, 'tcx>
 
     #[inline(always)]
     fn stack<'a>(
-        ecx: &'a InterpCx<'mir, 'tcx, Self>,
+        _ecx: &'a InterpCx<'mir, 'tcx, Self>,
     ) -> &'a [Frame<'mir, 'tcx, Self::Provenance, Self::FrameExtra>] {
-        &ecx.machine.stack
+        &[]
     }
 
     #[inline(always)]
     fn stack_mut<'a>(
-        ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
+        _ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
     ) -> &'a mut Vec<Frame<'mir, 'tcx, Self::Provenance, Self::FrameExtra>> {
-        &mut ecx.machine.stack
+        unreachable!()
     }
 }
 

compiler/rustc_mir_transform/src/const_prop_lint.rs

@@ -3,19 +3,16 @@
 
 use std::fmt::Debug;
 
-use rustc_const_eval::interpret::{ImmTy, MPlaceTy, Projectable};
-use rustc_const_eval::interpret::{InterpCx, InterpResult, OpTy, Scalar, StackPopCleanup};
+use rustc_const_eval::interpret::{ImmTy, Projectable};
+use rustc_const_eval::interpret::{InterpCx, InterpResult, OpTy, Scalar};
 use rustc_hir::def::DefKind;
 use rustc_hir::HirId;
 use rustc_index::bit_set::BitSet;
 use rustc_index::{Idx, IndexVec};
 use rustc_middle::mir::visit::Visitor;
 use rustc_middle::mir::*;
 use rustc_middle::ty::layout::{LayoutError, LayoutOf, LayoutOfHelpers, TyAndLayout};
-use rustc_middle::ty::GenericArgs;
-use rustc_middle::ty::{
-    self, ConstInt, Instance, ParamEnv, ScalarInt, Ty, TyCtxt, TypeVisitableExt,
-};
+use rustc_middle::ty::{self, ConstInt, ParamEnv, ScalarInt, Ty, TyCtxt, TypeVisitableExt};
 use rustc_span::Span;
 use rustc_target::abi::{Abi, FieldIdx, HasDataLayout, Size, TargetDataLayout, VariantIdx};
 
@@ -72,12 +69,13 @@ impl<'tcx> MirLint<'tcx> for ConstPropLint {
 
 /// Finds optimization opportunities on the MIR.
 struct ConstPropagator<'mir, 'tcx> {
-    ecx: InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>,
+    ecx: InterpCx<'mir, 'tcx, ConstPropMachine>,
     tcx: TyCtxt<'tcx>,
     param_env: ParamEnv<'tcx>,
     worklist: Vec<BasicBlock>,
     visited_blocks: BitSet<BasicBlock>,
     locals: IndexVec<Local, Value<'tcx>>,
+    body: &'mir Body<'tcx>,
 }
 
 #[derive(Debug, Clone)]
@@ -180,43 +178,29 @@ impl<'tcx> ty::layout::HasParamEnv<'tcx> for ConstPropagator<'_, 'tcx> {
 impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
     fn new(body: &'mir Body<'tcx>, tcx: TyCtxt<'tcx>) -> ConstPropagator<'mir, 'tcx> {
         let def_id = body.source.def_id();
-        let args = &GenericArgs::identity_for_item(tcx, def_id);
         let param_env = tcx.param_env_reveal_all_normalized(def_id);
 
         let can_const_prop = CanConstProp::check(tcx, param_env, body);
-        let mut ecx = InterpCx::new(
+        let ecx = InterpCx::new(
             tcx,
             tcx.def_span(def_id),
             param_env,
             ConstPropMachine::new(can_const_prop),
         );
 
-        let ret = MPlaceTy::fake_alloc_zst(ecx.layout_of(tcx.types.unit).unwrap()).into();
-
-        ecx.push_stack_frame(
-            Instance::new(def_id, args),
-            body,
-            &ret,
-            StackPopCleanup::Root { cleanup: false },
-        )
-        .expect("failed to push initial stack frame");
-
         ConstPropagator {
             ecx,
             tcx,
             param_env,
             worklist: vec![START_BLOCK],
             visited_blocks: BitSet::new_empty(body.basic_blocks.len()),
             locals: IndexVec::from_elem_n(Value::Uninit, body.local_decls.len()),
+            body,
         }
     }
 
-    fn body(&self) -> &'mir Body<'tcx> {
-        self.ecx.frame().body
-    }
-
     fn local_decls(&self) -> &'mir LocalDecls<'tcx> {
-        &self.body().local_decls
+        &self.body.local_decls
     }
 
     fn get_const(&self, place: Place<'tcx>) -> Option<&Value<'tcx>> {
@@ -243,7 +227,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
     }
 
     fn lint_root(&self, source_info: SourceInfo) -> Option<HirId> {
-        source_info.scope.lint_root(&self.body().source_scopes)
+        source_info.scope.lint_root(&self.body.source_scopes)
     }
 
     fn use_ecx<F, T>(&mut self, f: F) -> Option<T>
@@ -332,7 +316,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             // `AssertKind` only has an `OverflowNeg` variant, so make sure that is
             // appropriate to use.
             assert_eq!(op, UnOp::Neg, "Neg is the only UnOp that can overflow");
-            let source_info = self.body().source_info(location);
+            let source_info = self.body.source_info(location);
             self.report_assert_as_lint(
                 source_info,
                 AssertLint::ArithmeticOverflow(
@@ -370,7 +354,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             let r_bits = r.to_scalar().to_bits(right_size).ok();
             if r_bits.is_some_and(|b| b >= left_size.bits() as u128) {
                 debug!("check_binary_op: reporting assert for {:?}", location);
-                let source_info = self.body().source_info(location);
+                let source_info = self.body.source_info(location);
                 let panic = AssertKind::Overflow(
                     op,
                     match l {
@@ -398,7 +382,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                 let (_res, overflow) = this.ecx.overflowing_binary_op(op, &l, &r)?;
                 Ok(overflow)
             })? {
-                let source_info = self.body().source_info(location);
+                let source_info = self.body.source_info(location);
                 self.report_assert_as_lint(
                     source_info,
                     AssertLint::ArithmeticOverflow(
@@ -545,7 +529,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                 // Need proper const propagator for these.
                 _ => return None,
             };
-            let source_info = self.body().source_info(location);
+            let source_info = self.body.source_info(location);
             self.report_assert_as_lint(
                 source_info,
                 AssertLint::UnconditionalPanic(source_info.span, msg),
@@ -564,7 +548,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                         .layout_of(self.local_decls()[local].ty)
                         .map_or(true, |layout| layout.is_zst()),
                 "failed to remove values for `{local:?}`, value={val:?}: {:#?}",
-                self.body(),
+                self.body,
             )
         }
     }
@@ -580,7 +564,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             return None;
         }
         use rustc_middle::mir::Rvalue::*;
-        let layout = self.use_ecx(|this| this.ecx.eval_place(*dest))?.layout;
+        let layout = self.ecx.layout_of(dest.ty(self.body, self.tcx).ty).ok()?;
         trace!(?layout);
 
         let val: Value<'_> = match *rvalue {