From a10ac7d083d07a71c15d3c786cf2bd569f415b78 Mon Sep 17 00:00:00 2001
From: Oliver Scherer <github35764891676564198441@oli-obk.de>
Date: Wed, 3 Jun 2020 13:45:56 +0200
Subject: [PATCH] Don't intern memory in const prop.

This isn't sound without validation. We don't want to report errors in case of failure to intern and validate, we just don't want to const prop. Interning and const prop is not built for this, let's not do it until we have a clearer picture on aggregate propagation.
---
 src/librustc_mir/interpret/intern.rs     | 12 ++++++------
 src/librustc_mir/transform/const_prop.rs | 12 ++++--------
 2 files changed, 10 insertions(+), 14 deletions(-)

diff --git a/src/librustc_mir/interpret/intern.rs b/src/librustc_mir/interpret/intern.rs
index 02a7f24a1e351..4c1cf1b56ae66 100644
--- a/src/librustc_mir/interpret/intern.rs
+++ b/src/librustc_mir/interpret/intern.rs
@@ -294,7 +294,6 @@ pub enum InternKind {
     Static(hir::Mutability),
     Constant,
     Promoted,
-    ConstProp,
 }
 
 /// Intern `ret` and everything it references.
@@ -315,9 +314,7 @@ pub fn intern_const_alloc_recursive<M: CompileTimeMachine<'mir, 'tcx>>(
     let base_intern_mode = match intern_kind {
         InternKind::Static(mutbl) => InternMode::Static(mutbl),
         // FIXME: what about array lengths, array initializers?
-        InternKind::Constant | InternKind::ConstProp | InternKind::Promoted => {
-            InternMode::ConstBase
-        }
+        InternKind::Constant | InternKind::Promoted => InternMode::ConstBase,
     };
 
     // Type based interning.
@@ -359,7 +356,10 @@ pub fn intern_const_alloc_recursive<M: CompileTimeMachine<'mir, 'tcx>>(
             Err(error) => {
                 ecx.tcx.sess.delay_span_bug(
                     ecx.tcx.span,
-                    "error during interning should later cause validation failure",
+                    &format!(
+                        "error during interning should later cause validation failure: {}",
+                        error
+                    ),
                 );
                 // Some errors shouldn't come up because creating them causes
                 // an allocation, which we should avoid. When that happens,
@@ -400,7 +400,7 @@ pub fn intern_const_alloc_recursive<M: CompileTimeMachine<'mir, 'tcx>>(
                     // immutability is so important.
                     alloc.mutability = Mutability::Not;
                 }
-                InternKind::Constant | InternKind::ConstProp => {
+                InternKind::Constant => {
                     // If it's a constant, we should not have any "leftovers" as everything
                     // is tracked by const-checking.
                     // FIXME: downgrade this to a warning? It rejects some legitimate consts,
diff --git a/src/librustc_mir/transform/const_prop.rs b/src/librustc_mir/transform/const_prop.rs
index d6a27ae2e2684..cb5914b06c3c5 100644
--- a/src/librustc_mir/transform/const_prop.rs
+++ b/src/librustc_mir/transform/const_prop.rs
@@ -27,9 +27,9 @@ use rustc_trait_selection::traits;
 
 use crate::const_eval::error_to_const_error;
 use crate::interpret::{
-    self, compile_time_machine, intern_const_alloc_recursive, AllocId, Allocation, Frame, ImmTy,
-    Immediate, InternKind, InterpCx, LocalState, LocalValue, Memory, MemoryKind, OpTy,
-    Operand as InterpOperand, PlaceTy, Pointer, ScalarMaybeUninit, StackPopCleanup,
+    self, compile_time_machine, AllocId, Allocation, Frame, ImmTy, Immediate, InterpCx, LocalState,
+    LocalValue, Memory, MemoryKind, OpTy, Operand as InterpOperand, PlaceTy, Pointer,
+    ScalarMaybeUninit, StackPopCleanup,
 };
 use crate::transform::{MirPass, MirSource};
 
@@ -707,11 +707,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                 ScalarMaybeUninit::Scalar(l),
                 ScalarMaybeUninit::Scalar(r),
             )) => l.is_bits() && r.is_bits(),
-            interpret::Operand::Indirect(_) if mir_opt_level >= 2 => {
-                let mplace = op.assert_mem_place(&self.ecx);
-                intern_const_alloc_recursive(&mut self.ecx, InternKind::ConstProp, mplace, false);
-                true
-            }
+            interpret::Operand::Indirect(_) if mir_opt_level >= 2 => true,
             _ => false,
         }
     }