Remove control_flow_destroyed and properly lower && and ||

Author: ecstatic-morse

src/librustc_middle/mir/mod.rs

@@ -148,14 +148,6 @@ pub struct Body<'tcx> {
     /// Debug information pertaining to user variables, including captures.
     pub var_debug_info: Vec<VarDebugInfo<'tcx>>,
 
-    /// Mark this MIR of a const context other than const functions as having converted a `&&` or
-    /// `||` expression into `&` or `|` respectively. This is problematic because if we ever stop
-    /// this conversion from happening and use short circuiting, we will cause the following code
-    /// to change the value of `x`: `let mut x = 42; false && { x = 55; true };`
-    ///
-    /// List of places where control flow was destroyed. Used for error reporting.
-    pub control_flow_destroyed: Vec<(Span, String)>,
-
     /// A span representing this MIR, for error reporting.
     pub span: Span,
 
@@ -185,7 +177,6 @@ impl<'tcx> Body<'tcx> {
         arg_count: usize,
         var_debug_info: Vec<VarDebugInfo<'tcx>>,
         span: Span,
-        control_flow_destroyed: Vec<(Span, String)>,
         generator_kind: Option<GeneratorKind>,
     ) -> Self {
         // We need `arg_count` locals, and one for the return place.
@@ -212,7 +203,6 @@ impl<'tcx> Body<'tcx> {
             span,
             required_consts: Vec::new(),
             ignore_interior_mut_in_const_validation: false,
-            control_flow_destroyed,
             predecessor_cache: PredecessorCache::new(),
         }
     }
@@ -236,7 +226,6 @@ impl<'tcx> Body<'tcx> {
             spread_arg: None,
             span: DUMMY_SP,
             required_consts: Vec::new(),
-            control_flow_destroyed: Vec::new(),
             generator_kind: None,
             var_debug_info: Vec::new(),
             ignore_interior_mut_in_const_validation: false,

src/librustc_mir/shim.rs

@@ -251,7 +251,6 @@ fn new_body<'tcx>(
         arg_count,
         vec![],
         span,
-        vec![],
         None,
     )
 }

src/librustc_mir/transform/check_consts/validation.rs

@@ -207,8 +207,6 @@ impl Validator<'mir, 'tcx> {
             }
         }
 
-        check_short_circuiting_in_const_local(self.ccx);
-
         if body.is_cfg_cyclic() {
             // We can't provide a good span for the error here, but this should be caught by the
             // HIR const-checker anyways.
@@ -626,44 +624,6 @@ fn error_min_const_fn_violation(tcx: TyCtxt<'_>, span: Span, msg: Cow<'_, str>)
         .emit();
 }
 
-fn check_short_circuiting_in_const_local(ccx: &ConstCx<'_, 'tcx>) {
-    let body = ccx.body;
-
-    if body.control_flow_destroyed.is_empty() {
-        return;
-    }
-
-    let mut locals = body.vars_iter();
-    if let Some(local) = locals.next() {
-        let span = body.local_decls[local].source_info.span;
-        let mut error = ccx.tcx.sess.struct_span_err(
-            span,
-            &format!(
-                "new features like let bindings are not permitted in {}s \
-                which also use short circuiting operators",
-                ccx.const_kind(),
-            ),
-        );
-        for (span, kind) in body.control_flow_destroyed.iter() {
-            error.span_note(
-                *span,
-                &format!(
-                    "use of {} here does not actually short circuit due to \
-                     the const evaluator presently not being able to do control flow. \
-                     See issue #49146 <https://github.com/rust-lang/rust/issues/49146> \
-                     for more information.",
-                    kind
-                ),
-            );
-        }
-        for local in locals {
-            let span = body.local_decls[local].source_info.span;
-            error.span_note(span, "more locals are defined here");
-        }
-        error.emit();
-    }
-}
-
 fn check_return_ty_is_sync(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, hir_id: HirId) {
     let ty = body.return_ty();
     tcx.infer_ctxt().enter(|infcx| {

src/librustc_mir/transform/const_prop.rs

@@ -133,7 +133,6 @@ impl<'tcx> MirPass<'tcx> for ConstProp {
             body.arg_count,
             Default::default(),
             tcx.def_span(source.def_id()),
-            Default::default(),
             body.generator_kind,
         );
 

src/librustc_mir/transform/promote_consts.rs

@@ -1142,7 +1142,6 @@ pub fn promote_candidates<'tcx>(
             0,
             vec![],
             body.span,
-            vec![],
             body.generator_kind,
         );
         promoted.ignore_interior_mut_in_const_validation = true;

src/librustc_mir_build/build/mod.rs

@@ -778,7 +778,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             self.arg_count,
             self.var_debug_info,
             self.fn_span,
-            self.hir.control_flow_destroyed(),
             self.generator_kind,
         )
     }

src/librustc_mir_build/hair/cx/expr.rs

@@ -255,20 +255,6 @@ fn make_mirror_unadjusted<'a, 'tcx>(
             } else {
                 // FIXME overflow
                 match (op.node, cx.constness) {
-                    // Destroy control flow if `#![feature(const_if_match)]` is not enabled.
-                    (hir::BinOpKind::And, hir::Constness::Const)
-                        if !cx.tcx.features().const_if_match =>
-                    {
-                        cx.control_flow_destroyed.push((op.span, "`&&` operator".into()));
-                        ExprKind::Binary { op: BinOp::BitAnd, lhs: lhs.to_ref(), rhs: rhs.to_ref() }
-                    }
-                    (hir::BinOpKind::Or, hir::Constness::Const)
-                        if !cx.tcx.features().const_if_match =>
-                    {
-                        cx.control_flow_destroyed.push((op.span, "`||` operator".into()));
-                        ExprKind::Binary { op: BinOp::BitOr, lhs: lhs.to_ref(), rhs: rhs.to_ref() }
-                    }
-
                     (hir::BinOpKind::And, _) => ExprKind::LogicalOp {
                         op: LogicalOp::And,
                         lhs: lhs.to_ref(),

src/librustc_mir_build/hair/cx/mod.rs

@@ -47,9 +47,6 @@ crate struct Cx<'a, 'tcx> {
 
     /// Whether this constant/function needs overflow checks.
     check_overflow: bool,
-
-    /// See field with the same name on `mir::Body`.
-    control_flow_destroyed: Vec<(Span, String)>,
 }
 
 impl<'a, 'tcx> Cx<'a, 'tcx> {
@@ -89,13 +86,8 @@ impl<'a, 'tcx> Cx<'a, 'tcx> {
             body_owner: src_def_id.to_def_id(),
             body_owner_kind,
             check_overflow,
-            control_flow_destroyed: Vec::new(),
         }
     }
-
-    crate fn control_flow_destroyed(self) -> Vec<(Span, String)> {
-        self.control_flow_destroyed
-    }
 }
 
 impl<'a, 'tcx> Cx<'a, 'tcx> {