From 16dedba1c80e96e7b0481191d4ae16e2d8cb0016 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jannis=20Christopher=20K=C3=B6hl?= <mail@koehl.dev>
Date: Fri, 2 Sep 2022 00:37:38 +0200
Subject: [PATCH] Ignore terminators explicitly

---
 .../rustc_mir_dataflow/src/value_analysis.rs  | 20 ++++++++++++++-----
 .../src/dataflow_const_prop.rs                |  1 -
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/compiler/rustc_mir_dataflow/src/value_analysis.rs b/compiler/rustc_mir_dataflow/src/value_analysis.rs
index 64e45083fc07..5fe768f83106 100644
--- a/compiler/rustc_mir_dataflow/src/value_analysis.rs
+++ b/compiler/rustc_mir_dataflow/src/value_analysis.rs
@@ -146,10 +146,7 @@ pub trait ValueAnalysis<'tcx> {
             Rvalue::CopyForDeref(place) => {
                 self.handle_operand(&Operand::Copy(*place), state).into()
             }
-            _ => {
-                // FIXME: Check that other Rvalues really have no side-effect.
-                ValueOrPlaceOrRef::Unknown
-            }
+            _ => ValueOrPlaceOrRef::Unknown,
         }
     }
 
@@ -200,7 +197,20 @@ pub trait ValueAnalysis<'tcx> {
         self.super_terminator(terminator, state)
     }
 
-    fn super_terminator(&self, _terminator: &Terminator<'tcx>, _state: &mut State<Self::Value>) {}
+    fn super_terminator(&self, terminator: &Terminator<'tcx>, _state: &mut State<Self::Value>) {
+        match &terminator.kind {
+            TerminatorKind::Call { .. } | TerminatorKind::InlineAsm { .. } => {
+                // Effect is applied by `handle_call_return`.
+            }
+            TerminatorKind::DropAndReplace { .. } | TerminatorKind::Yield { .. } => {
+                // They would have an effect, but are not allowed in this phase.
+                bug!("encountered disallowed terminator");
+            }
+            _ => {
+                // The other terminators can be ignored.
+            }
+        }
+    }
 
     fn handle_call_return(
         &self,
diff --git a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
index f461514716e6..c80ff3dd3ec7 100644
--- a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
+++ b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
@@ -35,7 +35,6 @@ impl<'tcx> MirPass<'tcx> for DataflowConstProp {
     }
 }
 
-// FIXME: Consider support for discriminants, mutable references, arrays and slices.
 struct ConstAnalysis<'tcx> {
     map: Map,
     tcx: TyCtxt<'tcx>,