Do not clone body for ConstProp.

Author: cjgillot

compiler/rustc_mir_transform/src/const_prop.rs

@@ -94,34 +94,21 @@ impl<'tcx> MirPass<'tcx> for ConstProp {
 
         trace!("ConstProp starting for {:?}", def_id);
 
-        let dummy_body = &Body::new(
-            body.source,
-            (*body.basic_blocks).to_owned(),
-            body.source_scopes.clone(),
-            body.local_decls.clone(),
-            Default::default(),
-            body.arg_count,
-            Default::default(),
-            body.span,
-            body.generator_kind(),
-            body.tainted_by_errors,
-        );
-
         // FIXME(oli-obk, eddyb) Optimize locals (or even local paths) to hold
         // constants, instead of just checking for const-folding succeeding.
         // That would require a uniform one-def no-mutation analysis
         // and RPO (or recursing when needing the value of a local).
-        let mut optimization_finder = ConstPropagator::new(body, dummy_body, tcx);
+        let mut optimization_finder = ConstPropagator::new(body, tcx);
 
         // Traverse the body in reverse post-order, to ensure that `FullConstProp` locals are
         // assigned before being read.
-        let rpo = body.basic_blocks.reverse_postorder().to_vec();
-        for bb in rpo {
-            let data = &mut body.basic_blocks.as_mut_preserves_cfg()[bb];
+        for &bb in body.basic_blocks.reverse_postorder() {
+            let data = &body.basic_blocks[bb];
             optimization_finder.visit_basic_block_data(bb, data);
         }
 
-        optimization_finder.patch.visit_body_preserves_cfg(body);
+        let mut patch = optimization_finder.patch;
+        patch.visit_body_preserves_cfg(body);
 
         trace!("ConstProp done for {:?}", def_id);
     }
@@ -339,11 +326,7 @@ impl<'tcx> ty::layout::HasParamEnv<'tcx> for ConstPropagator<'_, 'tcx> {
 }
 
 impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
-    fn new(
-        body: &Body<'tcx>,
-        dummy_body: &'mir Body<'tcx>,
-        tcx: TyCtxt<'tcx>,
-    ) -> ConstPropagator<'mir, 'tcx> {
+    fn new(body: &'mir Body<'tcx>, tcx: TyCtxt<'tcx>) -> ConstPropagator<'mir, 'tcx> {
         let def_id = body.source.def_id();
         let args = &GenericArgs::identity_for_item(tcx, def_id);
         let param_env = tcx.param_env_reveal_all_normalized(def_id);
@@ -374,7 +357,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
 
         ecx.push_stack_frame(
             Instance::new(def_id, args),
-            dummy_body,
+            body,
             &ret,
             StackPopCleanup::Root { cleanup: false },
         )
@@ -390,7 +373,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
         }
 
         let patch = Patch::new(tcx);
-        ConstPropagator { ecx, tcx, param_env, local_decls: &dummy_body.local_decls, patch }
+        ConstPropagator { ecx, tcx, param_env, local_decls: &body.local_decls, patch }
     }
 
     fn get_const(&self, place: Place<'tcx>) -> Option<OpTy<'tcx>> {