X-Git-Url: https://git.lizzy.rs/?a=blobdiff_plain;f=compiler%2Frustc_middle%2Fsrc%2Fmir%2Fsyntax.rs;h=faf903a59490164f42733f41a91289eaf9aecf8d;hb=360db516ccf358bd4b35c483ae44634a74c66c0b;hp=6b4489026d3d379dee958125b73ced3eb3d40fb1;hpb=2dd2fb728e61a6e7912e1e2818407625ad806bb9;p=rust.git

diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
index 6b4489026d3..faf903a5949 100644
--- a/compiler/rustc_middle/src/mir/syntax.rs
+++ b/compiler/rustc_middle/src/mir/syntax.rs
@@ -286,7 +286,10 @@ pub enum StatementKind<'tcx> {
     /// This is permitted for both generators and ADTs. This does not necessarily write to the
     /// entire place; instead, it writes to the minimum set of bytes as required by the layout for
     /// the type.
-    SetDiscriminant { place: Box<Place<'tcx>>, variant_index: VariantIdx },
+    SetDiscriminant {
+        place: Box<Place<'tcx>>,
+        variant_index: VariantIdx,
+    },
 
     /// Deinitializes the place.
     ///
@@ -355,6 +358,8 @@ pub enum StatementKind<'tcx> {
     /// This avoids adding a new block and a terminator for simple intrinsics.
     Intrinsic(Box<NonDivergingIntrinsic<'tcx>>),
 
+    ConstEvalCounter,
+
     /// No-op. Useful for deleting instructions without affecting statement indices.
     Nop,
 }
@@ -512,6 +517,16 @@ pub struct CopyNonOverlapping<'tcx> {
 ///     must also be `cleanup`. This is a part of the type system and checked statically, so it is
 ///     still an error to have such an edge in the CFG even if it's known that it won't be taken at
 ///     runtime.
+///  4. The control flow between cleanup blocks must look like an upside down tree. Roughly
+///     speaking, this means that control flow that looks like a V is allowed, while control flow
+///     that looks like a W is not. This is necessary to ensure that landing pad information can be
+///     correctly codegened on MSVC. More precisely:
+///
+///     Begin with the standard control flow graph `G`. Modify `G` as follows: for any two cleanup
+///     vertices `u` and `v` such that `u` dominates `v`, contract `u` and `v` into a single vertex,
+///     deleting self edges and duplicate edges in the process. Now remove all vertices from `G`
+///     that are not cleanup vertices or are not reachable. The resulting graph must be an inverted
+///     tree, that is each vertex may have at most one successor and there may be no cycles.
 #[derive(Clone, TyEncodable, TyDecodable, Hash, HashStable, PartialEq, TypeFoldable, TypeVisitable)]
 pub enum TerminatorKind<'tcx> {
     /// Block has one successor; we continue execution there.