Remove a clone in mir/transform/add_validation.

Author: ljedrz

src/librustc_mir/transform/add_validation.rs

@@ -196,12 +196,13 @@ impl MirPass for AddValidation {
             return;
         }
         let restricted_validation = emit_validate == 1 && fn_contains_unsafe(tcx, src);
-        let local_decls = mir.local_decls.clone(); // FIXME: Find a way to get rid of this clone.
+        let (span, arg_count) = (mir.span, mir.arg_count);
+        let (basic_blocks, local_decls) = mir.basic_blocks_and_local_decls_mut();
 
         // Convert a place to a validation operand.
         let place_to_operand = |place: Place<'tcx>| -> ValidationOperand<'tcx, Place<'tcx>> {
-            let (re, mutbl) = place_context(&place, &local_decls, tcx);
-            let ty = place.ty(&local_decls, tcx).to_ty(tcx);
+            let (re, mutbl) = place_context(&place, local_decls, tcx);
+            let ty = place.ty(local_decls, tcx).to_ty(tcx);
             ValidationOperand { place, ty, re, mutbl }
         };
 
@@ -232,20 +233,20 @@ impl MirPass for AddValidation {
         {
             let source_info = SourceInfo {
                 scope: OUTERMOST_SOURCE_SCOPE,
-                span: mir.span, // FIXME: Consider using just the span covering the function
-                                // argument declaration.
+                span: span, // FIXME: Consider using just the span covering the function
+                            // argument declaration.
             };
             // Gather all arguments, skip return value.
-            let operands = mir.local_decls.iter_enumerated().skip(1).take(mir.arg_count)
+            let operands = local_decls.iter_enumerated().skip(1).take(arg_count)
                     .map(|(local, _)| place_to_operand(Place::Local(local))).collect();
-            emit_acquire(&mut mir.basic_blocks_mut()[START_BLOCK], source_info, operands);
+            emit_acquire(&mut basic_blocks[START_BLOCK], source_info, operands);
         }
 
         // PART 2
         // Add ReleaseValid/AcquireValid around function call terminators.  We don't use a visitor
         // because we need to access the block that a Call jumps to.
         let mut returns : Vec<(SourceInfo, Place<'tcx>, BasicBlock)> = Vec::new();
-        for block_data in mir.basic_blocks_mut() {
+        for block_data in basic_blocks.iter_mut() {
             match block_data.terminator {
                 Some(Terminator { kind: TerminatorKind::Call { ref args, ref destination, .. },
                                   source_info }) => {
@@ -298,7 +299,7 @@ impl MirPass for AddValidation {
         // Now we go over the returns we collected to acquire the return values.
         for (source_info, dest_place, dest_block) in returns {
             emit_acquire(
-                &mut mir.basic_blocks_mut()[dest_block],
+                &mut basic_blocks[dest_block],
                 source_info,
                 vec![place_to_operand(dest_place)]
             );
@@ -312,7 +313,7 @@ impl MirPass for AddValidation {
         // PART 3
         // Add ReleaseValid/AcquireValid around Ref and Cast.  Again an iterator does not seem very
         // suited as we need to add new statements before and after each Ref.
-        for block_data in mir.basic_blocks_mut() {
+        for block_data in basic_blocks {
             // We want to insert statements around Ref commands as we iterate.  To this end, we
             // iterate backwards using indices.
             for i in (0..block_data.statements.len()).rev() {