Preemptively invalidate derefs when entering a bb.

Author: cjgillot

compiler/rustc_mir_transform/src/gvn.rs

@@ -1851,6 +1851,13 @@ impl<'tcx> MutVisitor<'tcx> for VnState<'_, '_, 'tcx> {
         self.tcx
     }
 
+    fn visit_basic_block_data(&mut self, block: BasicBlock, bbdata: &mut BasicBlockData<'tcx>) {
+        // We do not track which block we would execute between the last and this one.
+        // In doubt, consider one of them may contain an indirect assignment and invalidate derefs.
+        self.invalidate_derefs();
+        self.super_basic_block_data(block, bbdata);
+    }
+
     fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
         self.simplify_place_projection(place, location);
         if context.is_mutating_use() && place.is_indirect() {

tests/mir-opt/gvn_clone.rs

@@ -1,5 +1,5 @@
 //@ test-mir-pass: GVN
-//@ compile-flags: -Zmir-enable-passes=+InstSimplify-before-inline
+//@ compile-flags: -Zmir-enable-passes=+InstSimplify-before-inline,+SimplifyCfg-after-unreachable-enum-branching
 
 // Check if we have transformed the default clone to copy in the specific pipeline.
 

tests/mir-opt/gvn_clone.{impl#0}-clone.GVN.diff

@@ -23,10 +23,6 @@
           _3 = copy _4;
 -         _2 = copy (*_3);
 +         _2 = copy ((*_1).0: i32);
-          goto -> bb1;
-      }
-  
-      bb1: {
           StorageDead(_3);
           StorageLive(_5);
           StorageLive(_6);
@@ -36,10 +32,6 @@
           _6 = copy _7;
 -         _5 = copy (*_6);
 +         _5 = copy ((*_1).1: u64);
-          goto -> bb2;
-      }
-  
-      bb2: {
           StorageDead(_6);
           StorageLive(_8);
           StorageLive(_9);
@@ -49,10 +41,6 @@
           _9 = copy _10;
 -         _8 = copy (*_9);
 +         _8 = copy ((*_1).2: [i8; 3]);
-          goto -> bb3;
-      }
-  
-      bb3: {
           StorageDead(_9);
 -         _0 = AllCopy { a: move _2, b: move _5, c: move _8 };
 -         StorageDead(_10);

tests/mir-opt/pre-codegen/slice_filter.variant_a-{closure#0}.PreCodegen.after.mir

@@ -5,83 +5,89 @@ fn variant_a::{closure#0}(_1: &mut {closure@$DIR/slice_filter.rs:7:25: 7:39}, _2
     let mut _3: &(usize, usize, usize, usize);
     let mut _6: bool;
     let mut _9: bool;
-    let mut _10: bool;
-    let _13: &usize;
-    let _14: &usize;
+    let mut _12: bool;
     let _15: &usize;
     let _16: &usize;
-    let mut _17: &&usize;
-    let mut _18: &&usize;
+    let _17: &usize;
+    let _18: &usize;
     let mut _19: &&usize;
     let mut _20: &&usize;
     let mut _21: &&usize;
     let mut _22: &&usize;
     let mut _23: &&usize;
     let mut _24: &&usize;
+    let mut _25: &&usize;
+    let mut _26: &&usize;
     scope 1 {
-        debug a => _13;
-        debug b => _14;
-        debug c => _15;
-        debug d => _16;
+        debug a => _15;
+        debug b => _16;
+        debug c => _17;
+        debug d => _18;
         scope 2 (inlined std::cmp::impls::<impl PartialOrd for &usize>::le) {
-            debug self => _17;
-            debug other => _18;
+            debug self => _19;
+            debug other => _20;
             scope 3 (inlined std::cmp::impls::<impl PartialOrd for usize>::le) {
-                debug self => _13;
-                debug other => _15;
+                debug self => _15;
+                debug other => _17;
                 let mut _4: usize;
                 let mut _5: usize;
             }
         }
         scope 4 (inlined std::cmp::impls::<impl PartialOrd for &usize>::le) {
-            debug self => _19;
-            debug other => _20;
+            debug self => _21;
+            debug other => _22;
             scope 5 (inlined std::cmp::impls::<impl PartialOrd for usize>::le) {
-                debug self => _16;
-                debug other => _14;
+                debug self => _18;
+                debug other => _16;
                 let mut _7: usize;
                 let mut _8: usize;
             }
         }
         scope 6 (inlined std::cmp::impls::<impl PartialOrd for &usize>::le) {
-            debug self => _21;
-            debug other => _22;
+            debug self => _23;
+            debug other => _24;
             scope 7 (inlined std::cmp::impls::<impl PartialOrd for usize>::le) {
-                debug self => _15;
-                debug other => _13;
+                debug self => _17;
+                debug other => _15;
+                let mut _10: usize;
+                let mut _11: usize;
             }
         }
         scope 8 (inlined std::cmp::impls::<impl PartialOrd for &usize>::le) {
-            debug self => _23;
-            debug other => _24;
+            debug self => _25;
+            debug other => _26;
             scope 9 (inlined std::cmp::impls::<impl PartialOrd for usize>::le) {
-                debug self => _14;
-                debug other => _16;
-                let mut _11: usize;
-                let mut _12: usize;
+                debug self => _16;
+                debug other => _18;
+                let mut _13: usize;
+                let mut _14: usize;
             }
         }
     }
 
     bb0: {
         _3 = copy (*_2);
-        // DBG: _13 = &((*_3).0: usize);
-        // DBG: _14 = &((*_3).1: usize);
-        // DBG: _15 = &((*_3).2: usize);
-        // DBG: _16 = &((*_3).3: usize);
+        // DBG: _15 = &((*_3).0: usize);
+        // DBG: _16 = &((*_3).1: usize);
+        // DBG: _17 = &((*_3).2: usize);
+        // DBG: _18 = &((*_3).3: usize);
         StorageLive(_6);
-        // DBG: _17 = &_13;
-        // DBG: _18 = &?;
+        // DBG: _19 = &_15;
+        // DBG: _20 = &?;
+        StorageLive(_4);
         _4 = copy ((*_3).0: usize);
+        StorageLive(_5);
         _5 = copy ((*_3).2: usize);
-        _6 = Le(copy _4, copy _5);
+        _6 = Le(move _4, move _5);
+        StorageDead(_5);
+        StorageDead(_4);
         switchInt(move _6) -> [0: bb2, otherwise: bb1];
     }
 
     bb1: {
         StorageLive(_9);
-        // DBG: _19 = &_16;
-        // DBG: _20 = &?;
+        // DBG: _21 = &_18;
+        // DBG: _22 = &?;
         StorageLive(_7);
         _7 = copy ((*_3).3: usize);
         StorageLive(_8);
@@ -93,11 +99,17 @@ fn variant_a::{closure#0}(_1: &mut {closure@$DIR/slice_filter.rs:7:25: 7:39}, _2
     }
 
     bb2: {
+        StorageLive(_12);
+        // DBG: _23 = &_17;
+        // DBG: _24 = &?;
         StorageLive(_10);
-        // DBG: _21 = &_15;
-        // DBG: _22 = &?;
-        _10 = Le(copy _5, copy _4);
-        switchInt(move _10) -> [0: bb3, otherwise: bb4];
+        _10 = copy ((*_3).2: usize);
+        StorageLive(_11);
+        _11 = copy ((*_3).0: usize);
+        _12 = Le(move _10, move _11);
+        StorageDead(_11);
+        StorageDead(_10);
+        switchInt(move _12) -> [0: bb3, otherwise: bb4];
     }
 
     bb3: {
@@ -106,20 +118,20 @@ fn variant_a::{closure#0}(_1: &mut {closure@$DIR/slice_filter.rs:7:25: 7:39}, _2
     }
 
     bb4: {
-        // DBG: _23 = &_14;
-        // DBG: _24 = &?;
-        StorageLive(_11);
-        _11 = copy ((*_3).1: usize);
-        StorageLive(_12);
-        _12 = copy ((*_3).3: usize);
-        _0 = Le(move _11, move _12);
-        StorageDead(_12);
-        StorageDead(_11);
+        // DBG: _25 = &_16;
+        // DBG: _26 = &?;
+        StorageLive(_13);
+        _13 = copy ((*_3).1: usize);
+        StorageLive(_14);
+        _14 = copy ((*_3).3: usize);
+        _0 = Le(move _13, move _14);
+        StorageDead(_14);
+        StorageDead(_13);
         goto -> bb5;
     }
 
     bb5: {
-        StorageDead(_10);
+        StorageDead(_12);
         goto -> bb7;
     }