From f13faf58d92d2d6154acc8cf50bf5d237a3a4118 Mon Sep 17 00:00:00 2001
From: Wesley Wiser <wwiser@gmail.com>
Date: Mon, 5 Aug 2019 20:01:59 -0400
Subject: [PATCH] Remove eval_promoted const-prop hack

---
 src/librustc_mir/const_eval.rs             | 23 +++-------------------
 src/librustc_mir/interpret/eval_context.rs |  6 +++++-
 src/librustc_mir/transform/const_prop.rs   |  7 ++-----
 3 files changed, 10 insertions(+), 26 deletions(-)

diff --git a/src/librustc_mir/const_eval.rs b/src/librustc_mir/const_eval.rs
index 4ab5c9cc1c498..67d63e52b2bfa 100644
--- a/src/librustc_mir/const_eval.rs
+++ b/src/librustc_mir/const_eval.rs
@@ -49,17 +49,6 @@ pub(crate) fn mk_eval_cx<'mir, 'tcx>(
     InterpCx::new(tcx.at(span), param_env, CompileTimeInterpreter::new(), Default::default())
 }
 
-pub(crate) fn eval_promoted<'mir, 'tcx>(
-    tcx: TyCtxt<'tcx>,
-    cid: GlobalId<'tcx>,
-    body: &'mir mir::Body<'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
-) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
-    let span = tcx.def_span(cid.instance.def_id());
-    let mut ecx = mk_eval_cx(tcx, span, param_env);
-    eval_body_using_ecx(&mut ecx, cid, body, param_env)
-}
-
 fn op_to_const<'tcx>(
     ecx: &CompileTimeEvalContext<'_, 'tcx>,
     op: OpTy<'tcx>,
@@ -360,7 +349,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
             }
         }
         // This is a const fn. Call it.
-        Ok(Some(match ecx.load_mir(instance.def) {
+        Ok(Some(match ecx.load_mir(instance.def, None) {
             Ok(body) => body,
             Err(err) => {
                 if let err_unsup!(NoMirFor(ref path)) = err.kind {
@@ -664,14 +653,8 @@ pub fn const_eval_raw_provider<'tcx>(
         Default::default()
     );
 
-    let res = ecx.load_mir(cid.instance.def);
-    res.map(|body| {
-        if let Some(index) = cid.promoted {
-           &tcx.promoted_mir(def_id)[index]
-        } else {
-            body
-        }
-    }).and_then(
+    let res = ecx.load_mir(cid.instance.def, cid.promoted);
+    res.and_then(
         |body| eval_body_using_ecx(&mut ecx, cid, body, key.param_env)
     ).and_then(|place| {
         Ok(RawConst {
diff --git a/src/librustc_mir/interpret/eval_context.rs b/src/librustc_mir/interpret/eval_context.rs
index 6f48396cdd7cf..ac01d436bdc9b 100644
--- a/src/librustc_mir/interpret/eval_context.rs
+++ b/src/librustc_mir/interpret/eval_context.rs
@@ -294,6 +294,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     pub fn load_mir(
         &self,
         instance: ty::InstanceDef<'tcx>,
+        promoted: Option<mir::Promoted>,
     ) -> InterpResult<'tcx, &'tcx mir::Body<'tcx>> {
         // do not continue if typeck errors occurred (can only occur in local crate)
         let did = instance.def_id();
@@ -303,7 +304,10 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         {
             throw_inval!(TypeckError)
         }
-        trace!("load mir {:?}", instance);
+        trace!("load mir(instance={:?}, promoted={:?})", instance, promoted);
+        if let Some(promoted) = promoted {
+            return Ok(&self.tcx.promoted_mir(did)[promoted]);
+        }
         match instance {
             ty::InstanceDef::Item(def_id) => if self.tcx.is_mir_available(did) {
                 Ok(self.tcx.optimized_mir(did))
diff --git a/src/librustc_mir/transform/const_prop.rs b/src/librustc_mir/transform/const_prop.rs
index 790595b4feef9..9aeef16ba1e38 100644
--- a/src/librustc_mir/transform/const_prop.rs
+++ b/src/librustc_mir/transform/const_prop.rs
@@ -27,7 +27,7 @@ use crate::interpret::{
     ImmTy, MemoryKind, StackPopCleanup, LocalValue, LocalState,
 };
 use crate::const_eval::{
-    CompileTimeInterpreter, error_to_const_error, eval_promoted, mk_eval_cx,
+    CompileTimeInterpreter, error_to_const_error, mk_eval_cx,
 };
 use crate::transform::{MirPass, MirSource};
 
@@ -297,11 +297,8 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                         instance,
                         promoted: Some(*promoted),
                     };
-                    // cannot use `const_eval` here, because that would require having the MIR
-                    // for the current function available, but we're producing said MIR right now
                     let res = self.use_ecx(source_info, |this| {
-                        let body = &this.tcx.promoted_mir(this.source.def_id())[*promoted];
-                        eval_promoted(this.tcx, cid, body, this.param_env)
+                        this.ecx.const_eval_raw(cid)
                     })?;
                     trace!("evaluated promoted {:?} to {:?}", promoted, res);
                     res.into()