Temp: remove unnecessary drop flags after monomorphization

matthewjasper · matthewjasper · commit 15beeeb01812 · 2019-11-24T12:28:39.000Z
diff --git a/src/librustc/mir/mod.rs b/src/librustc/mir/mod.rs
@@ -1088,8 +1088,18 @@ pub enum TerminatorKind<'tcx> {
     /// Indicates a terminator that can never be reached.
     Unreachable,
 
-    /// Drop the `Place`.
-    Drop { location: Place<'tcx>, target: BasicBlock, unwind: Option<BasicBlock> },
+    /// Drop the `Place`, possibly conditioned on a flag being true.
+    Drop {
+        location: Place<'tcx>,
+        /// Whether to drop the value.
+        ///
+        /// Before drop elaboration this is always `None. After drop elaboration
+        /// If this is `None` then the drop is unconditional, otherwise the drop
+        /// is only evaluated when the flag is true.
+        flag: Option<Place<'tcx>>,
+        target: BasicBlock,
+        unwind: Option<BasicBlock>,
+    },
 
     /// Drop the `Place` and assign the new value over it. This ensures
     /// that the assignment to `P` occurs *even if* the destructor for
@@ -1464,7 +1474,10 @@ impl<'tcx> TerminatorKind<'tcx> {
             Abort => write!(fmt, "abort"),
             Yield { ref value, .. } => write!(fmt, "_1 = suspend({:?})", value),
             Unreachable => write!(fmt, "unreachable"),
-            Drop { ref location, .. } => write!(fmt, "drop({:?})", location),
+            Drop { ref location, flag: Some(ref flag), .. } => {
+                write!(fmt, "if {:?} drop({:?})", flag, location)
+            }
+            Drop { ref location, flag: None, .. } => write!(fmt, "drop({:?})", location),
             DropAndReplace { ref location, ref value, .. } => {
                 write!(fmt, "replace({:?} <- {:?})", location, value)
             }
@@ -2967,8 +2980,13 @@ impl<'tcx> TypeFoldable<'tcx> for Terminator<'tcx> {
                 values: values.clone(),
                 targets: targets.clone(),
             },
-            Drop { ref location, target, unwind } => {
-                Drop { location: location.fold_with(folder), target, unwind }
+            Drop { ref location, ref flag, target, unwind } => {
+                Drop {
+                    location: location.fold_with(folder),
+                    flag: flag.fold_with(folder),
+                    target,
+                    unwind,
+                }
             }
             DropAndReplace { ref location, ref value, target, unwind } => DropAndReplace {
                 location: location.fold_with(folder),
@@ -3025,7 +3043,9 @@ impl<'tcx> TypeFoldable<'tcx> for Terminator<'tcx> {
             SwitchInt { ref discr, switch_ty, .. } => {
                 discr.visit_with(visitor) || switch_ty.visit_with(visitor)
             }
-            Drop { ref location, .. } => location.visit_with(visitor),
+            Drop { ref location, ref flag, .. } => {
+                location.visit_with(visitor) || flag.visit_with(visitor)
+            },
             DropAndReplace { ref location, ref value, .. } => {
                 location.visit_with(visitor) || value.visit_with(visitor)
             }
diff --git a/src/librustc/mir/visit.rs b/src/librustc/mir/visit.rs
@@ -432,14 +432,22 @@ macro_rules! make_mir_visitor {
 
                     TerminatorKind::Drop {
                         location,
+                        flag,
                         target: _,
                         unwind: _,
                     } => {
                         self.visit_place(
                             location,
                             PlaceContext::MutatingUse(MutatingUseContext::Drop),
-                            source_location
+                            source_location,
                         );
+                        if let Some(flag) = flag {
+                            self.visit_place(
+                                flag,
+                                PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
+                                source_location,
+                            );
+                        }
                     }
 
                     TerminatorKind::DropAndReplace {
diff --git a/src/librustc_codegen_ssa/mir/block.rs b/src/librustc_codegen_ssa/mir/block.rs
@@ -321,8 +321,10 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         helper: TerminatorCodegenHelper<'b, 'tcx>,
         mut bx: Bx,
         location: &mir::Place<'tcx>,
+        flag: &Option<mir::Place<'tcx>>,
         target: mir::BasicBlock,
         unwind: Option<mir::BasicBlock>,
+        source_info: mir::SourceInfo,
     ) {
         let ty = location.ty(self.mir, bx.tcx()).ty;
         let ty = self.monomorphize(&ty);
@@ -335,6 +337,16 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             return
         }
 
+        if let Some(flag) = flag {
+            let flag = self.codegen_consume(&mut bx, &flag.as_ref()).immediate();
+            let lltarget = helper.llblock(self, target);
+            let drop_block = self.new_block("drop");
+            helper.maybe_sideeffect(self.mir, &mut bx, &[target]);
+            bx.cond_br(flag, drop_block.llbb(), lltarget);
+            bx = drop_block;
+            self.set_debug_loc(&mut bx, source_info);
+        }
+
         let place = self.codegen_place(&mut bx, &location.as_ref());
         let (args1, args2);
         let mut args = if let Some(llextra) = place.llextra {
@@ -854,8 +866,16 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 bx.unreachable();
             }
 
-            mir::TerminatorKind::Drop { ref location, target, unwind } => {
-                self.codegen_drop_terminator(helper, bx, location, target, unwind);
+            mir::TerminatorKind::Drop { ref location, ref flag, target, unwind } => {
+                self.codegen_drop_terminator(
+                    helper,
+                    bx,
+                    location,
+                    flag,
+                    target,
+                    unwind,
+                    terminator.source_info,
+                );
             }
 
             mir::TerminatorKind::Assert { ref cond, expected, ref msg, target, cleanup } => {
diff --git a/src/librustc_mir/borrow_check/mod.rs b/src/librustc_mir/borrow_check/mod.rs
@@ -618,6 +618,7 @@ impl<'cx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx
             }
             TerminatorKind::Drop {
                 location: ref drop_place,
+                flag: _,
                 target: _,
                 unwind: _,
             } => {
diff --git a/src/librustc_mir/borrow_check/nll/invalidation.rs b/src/librustc_mir/borrow_check/nll/invalidation.rs
@@ -155,6 +155,7 @@ impl<'cx, 'tcx> Visitor<'tcx> for InvalidationGenerator<'cx, 'tcx> {
             }
             TerminatorKind::Drop {
                 location: ref drop_place,
+                flag: _,
                 target: _,
                 unwind: _,
             } => {
diff --git a/src/librustc_mir/build/scope.rs b/src/librustc_mir/build/scope.rs
@@ -352,6 +352,7 @@ impl DropTree {
                 DropKind::Value => {
                     let terminator = TerminatorKind::Drop {
                         target: blocks[drop_data.1].unwrap(),
+                        flag: None,
                         // The caller will handle this if needed.
                         unwind: None,
                         location: drop_data.0.local.into(),
@@ -1250,6 +1251,7 @@ fn build_scope_drops<'tcx>(
                 let next = cfg.start_new_block();
                 cfg.terminate(block, source_info, TerminatorKind::Drop {
                     location: local.into(),
+                    flag: None,
                     target: next,
                     unwind: None
                 });
diff --git a/src/librustc_mir/dataflow/generic.rs b/src/librustc_mir/dataflow/generic.rs
@@ -480,7 +480,7 @@ where
             mir::TerminatorKind::Goto { target }
             | mir::TerminatorKind::Assert { target, cleanup: None, .. }
             | mir::TerminatorKind::Yield { resume: target, drop: None, .. }
-            | mir::TerminatorKind::Drop { target, location: _, unwind: None }
+            | mir::TerminatorKind::Drop { target, location: _, unwind: None, flag: _ }
             | mir::TerminatorKind::DropAndReplace { target, value: _, location: _, unwind: None } =>
             {
                 self.propagate_bits_into_entry_set_for(in_out, target, dirty_list);
@@ -492,7 +492,7 @@ where
             }
 
             mir::TerminatorKind::Assert { target, cleanup: Some(unwind), .. }
-            | mir::TerminatorKind::Drop { target, location: _, unwind: Some(unwind) }
+            | mir::TerminatorKind::Drop { target, location: _, unwind: Some(unwind), flag: _ }
             | mir::TerminatorKind::DropAndReplace {
                 target,
                 value: _,
diff --git a/src/librustc_mir/dataflow/mod.rs b/src/librustc_mir/dataflow/mod.rs
@@ -840,7 +840,7 @@ where
             mir::TerminatorKind::Goto { target } |
             mir::TerminatorKind::Assert { target, cleanup: None, .. } |
             mir::TerminatorKind::Yield { resume: target, drop: None, .. } |
-            mir::TerminatorKind::Drop { target, location: _, unwind: None } |
+            mir::TerminatorKind::Drop { target, location: _, unwind: None, flag: _ } |
             mir::TerminatorKind::DropAndReplace {
                 target, value: _, location: _, unwind: None
             } => {
@@ -851,7 +851,7 @@ where
                 self.propagate_bits_into_entry_set_for(in_out, drop, dirty_list);
             }
             mir::TerminatorKind::Assert { target, cleanup: Some(unwind), .. } |
-            mir::TerminatorKind::Drop { target, location: _, unwind: Some(unwind) } |
+            mir::TerminatorKind::Drop { target, location: _, unwind: Some(unwind), flag: _ } |
             mir::TerminatorKind::DropAndReplace {
                 target, value: _, location: _, unwind: Some(unwind)
             } => {
diff --git a/src/librustc_mir/dataflow/move_paths/builder.rs b/src/librustc_mir/dataflow/move_paths/builder.rs
@@ -368,7 +368,7 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
                 self.gather_operand(value);
             }
 
-            TerminatorKind::Drop { ref location, target: _, unwind: _ } => {
+            TerminatorKind::Drop { ref location, target: _, unwind: _, flag: _ } => {
                 self.gather_move(location);
             }
             TerminatorKind::DropAndReplace { ref location, ref value, .. } => {
diff --git a/src/librustc_mir/interpret/terminator.rs b/src/librustc_mir/interpret/terminator.rs
@@ -105,6 +105,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
             Drop {
                 ref location,
+                ref flag,
                 target,
                 unwind,
             } => {
@@ -113,14 +114,22 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let ty = place.layout.ty;
                 trace!("TerminatorKind::drop: {:?}, type {}", location, ty);
 
-                let instance = Instance::resolve_drop_in_place(*self.tcx, ty);
-                self.drop_in_place(
-                    place,
-                    instance,
-                    terminator.source_info.span,
-                    target,
-                    unwind
-                )?;
+                let should_drop = if let Some(flag) = flag {
+                    let imm = self.read_scalar(self.eval_place_to_op(flag, None)?)?.not_undef()?;
+                    imm.to_bool()?
+                } else {
+                    true
+                };
+                if should_drop {
+                    let instance = Instance::resolve_drop_in_place(*self.tcx, ty);
+                    self.drop_in_place(
+                        place,
+                        instance,
+                        terminator.source_info.span,
+                        target,
+                        unwind
+                    )?;
+                }
             }
 
             Assert {
diff --git a/src/librustc_mir/shim.rs b/src/librustc_mir/shim.rs
@@ -281,7 +281,7 @@ impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
         }
     }
 
-    fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
+    fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Place<'tcx>> {
         None
     }
 
@@ -617,6 +617,7 @@ impl CloneShimBuilder<'tcx> {
         // `drop(dest[beg])`;
         self.block(vec![], TerminatorKind::Drop {
             location: self.tcx.mk_place_index(dest, beg),
+            flag: None,
             target: BasicBlock::new(8),
             unwind: None,
         }, true);
@@ -674,6 +675,7 @@ impl CloneShimBuilder<'tcx> {
                 // Drop previous field and goto previous cleanup block.
                 self.block(vec![], TerminatorKind::Drop {
                     location: previous_field,
+                    flag: None,
                     target: previous_cleanup,
                     unwind: None,
                 }, true);
@@ -808,6 +810,7 @@ fn build_call_shim<'tcx>(
         // BB #1 - drop for Self
         block(&mut blocks, vec![], TerminatorKind::Drop {
             location: Place::from(rcvr_arg),
+            flag: None,
             target: BasicBlock::new(2),
             unwind: None
         }, false);
@@ -818,6 +821,7 @@ fn build_call_shim<'tcx>(
         // BB #3 - drop if closure panics
         block(&mut blocks, vec![], TerminatorKind::Drop {
             location: Place::from(rcvr_arg),
+            flag: None,
             target: BasicBlock::new(4),
             unwind: None
         }, true);
diff --git a/src/librustc_mir/transform/add_moves_for_packed_drops.rs b/src/librustc_mir/transform/add_moves_for_packed_drops.rs
@@ -90,9 +90,9 @@ fn add_move_for_packed_drop<'tcx>(
     is_cleanup: bool,
 ) {
     debug!("add_move_for_packed_drop({:?} @ {:?})", terminator, loc);
-    let (location, target, unwind) = match terminator.kind {
-        TerminatorKind::Drop { ref location, target, unwind } =>
-            (location, target, unwind),
+    let (location, flag, target, unwind) = match terminator.kind {
+        TerminatorKind::Drop { ref location, ref flag, target, unwind } =>
+            (location, flag, target, unwind),
         _ => unreachable!()
     };
 
@@ -116,6 +116,7 @@ fn add_move_for_packed_drop<'tcx>(
                      Rvalue::Use(Operand::Move(location.clone())));
     patch.patch_terminator(loc.block, TerminatorKind::Drop {
         location: Place::from(temp),
+        flag: flag.clone(),
         target: storage_dead_block,
         unwind
     });
diff --git a/src/librustc_mir/transform/elaborate_drops.rs b/src/librustc_mir/transform/elaborate_drops.rs
@@ -257,8 +257,8 @@ impl<'a, 'b, 'tcx> DropElaborator<'a, 'tcx> for Elaborator<'a, 'b, 'tcx> {
         })
     }
 
-    fn get_drop_flag(&mut self, path: Self::Path) -> Option<Operand<'tcx>> {
-        self.ctxt.drop_flag(path).map(Operand::Copy)
+    fn get_drop_flag(&mut self, path: Self::Path) -> Option<Place<'tcx>> {
+        self.ctxt.drop_flag(path)
     }
 }
 
@@ -374,10 +374,14 @@ impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
 
             let resume_block = self.patch.resume_block();
             match terminator.kind {
-                TerminatorKind::Drop { ref location, target, unwind } => {
+                TerminatorKind::Drop { ref location, ref flag, target, unwind } => {
                     let init_data = self.initialization_data_at(loc);
                     match self.move_data().rev_lookup.find(location.as_ref()) {
                         LookupResult::Exact(path) => {
+                            debug_assert!(
+                                flag.is_none(),
+                                "should not have drop flags before elaboration",
+                            );
                             elaborate_drop(
                                 &mut Elaborator {
                                     init_data: &init_data,
@@ -494,6 +498,7 @@ impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
                 debug!("elaborate_drop_and_replace({:?}) - untracked {:?}", terminator, parent);
                 self.patch.patch_terminator(bb, TerminatorKind::Drop {
                     location: location.clone(),
+                    flag: None,
                     target,
                     unwind: Some(unwind)
                 });
diff --git a/src/librustc_mir/transform/generator.rs b/src/librustc_mir/transform/generator.rs
@@ -894,6 +894,7 @@ fn elaborate_generator_drops<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, body: &mut
                 source_info,
                 kind: TerminatorKind::Drop {
                     location,
+                    flag: None,
                     target,
                     unwind
                 }
@@ -1109,6 +1110,7 @@ fn insert_clean_drop(body: &mut Body<'_>) -> BasicBlock {
     let drop_clean = BasicBlock::new(body.basic_blocks().len());
     let term = TerminatorKind::Drop {
         location: Place::from(self_arg()),
+        flag: None,
         target: return_block,
         unwind: None,
     };
diff --git a/src/librustc_mir/transform/inline.rs b/src/librustc_mir/transform/inline.rs
@@ -303,7 +303,7 @@ impl Inliner<'tcx> {
             let term = blk.terminator();
             let mut is_drop = false;
             match term.kind {
-                TerminatorKind::Drop { ref location, target, unwind } |
+                TerminatorKind::Drop { ref location, target, unwind, .. } |
                 TerminatorKind::DropAndReplace { ref location, target, unwind, .. } => {
                     is_drop = true;
                     work_list.push(target);
diff --git a/src/librustc_mir/util/elaborate_drops.rs b/src/librustc_mir/util/elaborate_drops.rs

Original file line number	Diff line number	Diff line change
`@@ -618,6 +618,7 @@ impl<'cx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx, 'tcx`
`618`	`618`	`}`
`619`	`619`	`TerminatorKind::Drop {`
`620`	`620`	`location: ref drop_place,`
	`621`	`+ flag: _,`
`621`	`622`	`target: _,`
`622`	`623`	`unwind: _,`
`623`	`624`	`} => {`
Original file line number	Diff line number	Diff line change
`@@ -155,6 +155,7 @@ impl<'cx, 'tcx> Visitor<'tcx> for InvalidationGenerator<'cx, 'tcx> {`
`155`	`155`	`}`
`156`	`156`	`TerminatorKind::Drop {`
`157`	`157`	`location: ref drop_place,`
	`158`	`+ flag: _,`
`158`	`159`	`target: _,`
`159`	`160`	`unwind: _,`
`160`	`161`	`} => {`
Original file line number	Diff line number	Diff line change
`@@ -368,7 +368,7 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {`
`368`	`368`	`self.gather_operand(value);`
`369`	`369`	`}`
`370`	`370`
`371`		`- TerminatorKind::Drop { ref location, target: _, unwind: _ } => {`
	`371`	`+ TerminatorKind::Drop { ref location, target: _, unwind: _, flag: _ } => {`
`372`	`372`	`self.gather_move(location);`
`373`	`373`	`}`
`374`	`374`	`TerminatorKind::DropAndReplace { ref location, ref value, .. } => {`