Rollup merge of #72820 - jonas-schievink:instcombine-uninit, r=oli-obk

InstCombine: Don't optimize `&mut *x` into `x`

Fixes #72797

Author: Dylan-DPC

src/librustc_mir/transform/instcombine.rs

@@ -1,11 +1,12 @@
 //! Performs various peephole optimizations.
 
 use crate::transform::{MirPass, MirSource};
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_hir::Mutability;
 use rustc_index::vec::Idx;
 use rustc_middle::mir::visit::{MutVisitor, Visitor};
 use rustc_middle::mir::{
-    Body, Constant, Local, Location, Mutability, Operand, Place, PlaceRef, ProjectionElem, Rvalue,
+    Body, Constant, Local, Location, Operand, Place, PlaceRef, ProjectionElem, Rvalue,
 };
 use rustc_middle::ty::{self, TyCtxt};
 use std::mem;
@@ -39,7 +40,7 @@ impl<'tcx> MutVisitor<'tcx> for InstCombineVisitor<'tcx> {
     }
 
     fn visit_rvalue(&mut self, rvalue: &mut Rvalue<'tcx>, location: Location) {
-        if let Some(mtbl) = self.optimizations.and_stars.remove(&location) {
+        if self.optimizations.and_stars.remove(&location) {
             debug!("replacing `&*`: {:?}", rvalue);
             let new_place = match rvalue {
                 Rvalue::Ref(_, _, place) => {
@@ -57,10 +58,7 @@ impl<'tcx> MutVisitor<'tcx> for InstCombineVisitor<'tcx> {
                 }
                 _ => bug!("Detected `&*` but didn't find `&*`!"),
             };
-            *rvalue = Rvalue::Use(match mtbl {
-                Mutability::Mut => Operand::Move(new_place),
-                Mutability::Not => Operand::Copy(new_place),
-            });
+            *rvalue = Rvalue::Use(Operand::Copy(new_place))
         }
 
         if let Some(constant) = self.optimizations.arrays_lengths.remove(&location) {
@@ -93,8 +91,8 @@ impl Visitor<'tcx> for OptimizationFinder<'b, 'tcx> {
             {
                 // The dereferenced place must have type `&_`.
                 let ty = Place::ty_from(local, proj_base, self.body, self.tcx).ty;
-                if let ty::Ref(_, _, mtbl) = ty.kind {
-                    self.optimizations.and_stars.insert(location, mtbl);
+                if let ty::Ref(_, _, Mutability::Not) = ty.kind {
+                    self.optimizations.and_stars.insert(location);
                 }
             }
         }
@@ -114,6 +112,6 @@ impl Visitor<'tcx> for OptimizationFinder<'b, 'tcx> {
 
 #[derive(Default)]
 struct OptimizationList<'tcx> {
-    and_stars: FxHashMap<Location, Mutability>,
+    and_stars: FxHashSet<Location>,
     arrays_lengths: FxHashMap<Location, Constant<'tcx>>,
 }

src/test/mir-opt/inline/issue-58867-inline-as-ref-as-mut/rustc.a.Inline.after.mir

@@ -8,14 +8,18 @@ fn a(_1: &mut [T]) -> &mut [T] {
     let mut _4: &mut [T];                // in scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:6
     scope 1 {
         debug self => _4;                // in scope 1 at $SRC_DIR/libcore/convert/mod.rs:LL:COL
+        let mut _5: &mut [T];            // in scope 1 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:15
     }
 
     bb0: {
         StorageLive(_2);                 // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:15
         StorageLive(_3);                 // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:15
         StorageLive(_4);                 // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:6
         _4 = &mut (*_1);                 // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:6
-        _3 = move _4;                    // scope 1 at $SRC_DIR/libcore/convert/mod.rs:LL:COL
+        StorageLive(_5);                 // scope 1 at $SRC_DIR/libcore/convert/mod.rs:LL:COL
+        _5 = &mut (*_4);                 // scope 1 at $SRC_DIR/libcore/convert/mod.rs:LL:COL
+        _3 = &mut (*_5);                 // scope 1 at $SRC_DIR/libcore/convert/mod.rs:LL:COL
+        StorageDead(_5);                 // scope 1 at $SRC_DIR/libcore/convert/mod.rs:LL:COL
         _2 = &mut (*_3);                 // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:15
         StorageDead(_4);                 // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:14: 3:15
         _0 = &mut (*_2);                 // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:3:5: 3:15

src/test/mir-opt/inline/issue-58867-inline-as-ref-as-mut/rustc.b.Inline.after.mir

@@ -9,6 +9,7 @@ fn b(_1: &mut std::boxed::Box<T>) -> &mut T {
     scope 1 {
         debug self => _4;                // in scope 1 at $SRC_DIR/liballoc/boxed.rs:LL:COL
         let mut _5: &mut T;              // in scope 1 at $DIR/issue-58867-inline-as-ref-as-mut.rs:8:5: 8:15
+        let mut _6: &mut T;              // in scope 1 at $DIR/issue-58867-inline-as-ref-as-mut.rs:8:5: 8:15
     }
 
     bb0: {
@@ -17,8 +18,11 @@ fn b(_1: &mut std::boxed::Box<T>) -> &mut T {
         StorageLive(_4);                 // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:8:5: 8:6
         _4 = &mut (*_1);                 // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:8:5: 8:6
         StorageLive(_5);                 // scope 1 at $SRC_DIR/liballoc/boxed.rs:LL:COL
-        _5 = &mut (*(*_4));              // scope 1 at $SRC_DIR/liballoc/boxed.rs:LL:COL
-        _3 = move _5;                    // scope 1 at $SRC_DIR/liballoc/boxed.rs:LL:COL
+        StorageLive(_6);                 // scope 1 at $SRC_DIR/liballoc/boxed.rs:LL:COL
+        _6 = &mut (*(*_4));              // scope 1 at $SRC_DIR/liballoc/boxed.rs:LL:COL
+        _5 = &mut (*_6);                 // scope 1 at $SRC_DIR/liballoc/boxed.rs:LL:COL
+        _3 = &mut (*_5);                 // scope 1 at $SRC_DIR/liballoc/boxed.rs:LL:COL
+        StorageDead(_6);                 // scope 1 at $SRC_DIR/liballoc/boxed.rs:LL:COL
         StorageDead(_5);                 // scope 1 at $SRC_DIR/liballoc/boxed.rs:LL:COL
         _2 = &mut (*_3);                 // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:8:5: 8:15
         StorageDead(_4);                 // scope 0 at $DIR/issue-58867-inline-as-ref-as-mut.rs:8:14: 8:15

src/test/mir-opt/nrvo-simple/rustc.nrvo.RenameReturnPlace.diff

@@ -26,12 +26,17 @@
                                            // + span: $DIR/nrvo-simple.rs:3:20: 3:21
                                            // + literal: Const { ty: u8, val: Value(Scalar(0x00)) }
           StorageLive(_3);                 // scope 1 at $DIR/nrvo-simple.rs:4:5: 4:19
+          StorageLive(_5);                 // scope 1 at $DIR/nrvo-simple.rs:4:10: 4:18
+          StorageLive(_6);                 // scope 1 at $DIR/nrvo-simple.rs:4:10: 4:18
 -         _6 = &mut _2;                    // scope 1 at $DIR/nrvo-simple.rs:4:10: 4:18
 +         _6 = &mut _0;                    // scope 1 at $DIR/nrvo-simple.rs:4:10: 4:18
-          _3 = move _1(move _6) -> bb1;    // scope 1 at $DIR/nrvo-simple.rs:4:5: 4:19
+          _5 = &mut (*_6);                 // scope 1 at $DIR/nrvo-simple.rs:4:10: 4:18
+          _3 = move _1(move _5) -> bb1;    // scope 1 at $DIR/nrvo-simple.rs:4:5: 4:19
       }
 
       bb1: {
+          StorageDead(_5);                 // scope 1 at $DIR/nrvo-simple.rs:4:18: 4:19
+          StorageDead(_6);                 // scope 1 at $DIR/nrvo-simple.rs:4:19: 4:20
           StorageDead(_3);                 // scope 1 at $DIR/nrvo-simple.rs:4:19: 4:20
 -         _0 = _2;                         // scope 1 at $DIR/nrvo-simple.rs:5:5: 5:8
 -         StorageDead(_2);                 // scope 0 at $DIR/nrvo-simple.rs:6:1: 6:2