Create stable metric to measure long computation in Const Eval

This patch adds a `MirPass` that tracks the number of back-edges and
function calls in the CFG, adds a new MIR instruction to increment a
counter every time they are encountered during Const Eval, and emit a
warning if a configured limit is breached.

4 files changed, 6 insertions, 2 deletions

diff --git a/compiler/rustc_borrowck/src/dataflow.rs b/compiler/rustc_borrowck/src/dataflow.rs
index 8c4885770ad..2821677c537 100644
--- a/compiler/rustc_borrowck/src/dataflow.rs
+++ b/compiler/rustc_borrowck/src/dataflow.rs
@@ -393,6 +393,7 @@ impl<'tcx> rustc_mir_dataflow::GenKillAnalysis<'tcx> for Borrows<'_, 'tcx> {
             | mir::StatementKind::AscribeUserType(..)
             | mir::StatementKind::Coverage(..)
             | mir::StatementKind::Intrinsic(..)
+            | mir::StatementKind::ConstEvalCounter
             | mir::StatementKind::Nop => {}
         }
     }
diff --git a/compiler/rustc_borrowck/src/invalidation.rs b/compiler/rustc_borrowck/src/invalidation.rs
index 6fd9290058c..6217676d5c1 100644
--- a/compiler/rustc_borrowck/src/invalidation.rs
+++ b/compiler/rustc_borrowck/src/invalidation.rs
@@ -91,7 +91,8 @@ impl<'cx, 'tcx> Visitor<'tcx> for InvalidationGenerator<'cx, 'tcx> {
                     LocalMutationIsAllowed::Yes,
                 );
             }
-            StatementKind::Nop
+            StatementKind::ConstEvalCounter
+            | StatementKind::Nop
             | StatementKind::Retag { .. }
             | StatementKind::Deinit(..)
             | StatementKind::SetDiscriminant { .. } => {
diff --git a/compiler/rustc_borrowck/src/lib.rs b/compiler/rustc_borrowck/src/lib.rs
index 73ea7314b75..8f8fae2c630 100644
--- a/compiler/rustc_borrowck/src/lib.rs
+++ b/compiler/rustc_borrowck/src/lib.rs
@@ -620,7 +620,8 @@ impl<'cx, 'tcx> rustc_mir_dataflow::ResultsVisitor<'cx, 'tcx> for MirBorrowckCtx
                     flow_state,
                 );
             }
-            StatementKind::Nop
+            StatementKind::ConstEvalCounter
+            | StatementKind::Nop
             | StatementKind::Retag { .. }
             | StatementKind::Deinit(..)
             | StatementKind::SetDiscriminant { .. } => {
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index 81bd4c2a783..06087b0c579 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -1258,6 +1258,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             | StatementKind::StorageDead(..)
             | StatementKind::Retag { .. }
             | StatementKind::Coverage(..)
+            | StatementKind::ConstEvalCounter
             | StatementKind::Nop => {}
             StatementKind::Deinit(..) | StatementKind::SetDiscriminant { .. } => {
                 bug!("Statement not allowed in this MIR phase")