Auto merge of #115105 - cjgillot:dest-prop-default, r=oli-obk

Enable DestinationPropagation by default.

~~Based on https://github.com/rust-lang/rust/pull/115291.~~

This PR proposes to enable the destination propagation pass by default.
This pass is meant to reduce the amount of copies present in MIR.

At the same time, this PR removes the `RenameReturnPlace` pass, as it is currently unsound.
`DestinationPropagation` is not limited to `_0`, but does not handle borrowed locals.

1 files changed, 35 insertions, 39 deletions

diff --git a/tests/mir-opt/pre-codegen/slice_iter.reverse_loop.PreCodegen.after.panic-unwind.mir b/tests/mir-opt/pre-codegen/slice_iter.reverse_loop.PreCodegen.after.panic-unwind.mir
index c7cd37afd86..5a2d9d2a681 100644
--- a/tests/mir-opt/pre-codegen/slice_iter.reverse_loop.PreCodegen.after.panic-unwind.mir
+++ b/tests/mir-opt/pre-codegen/slice_iter.reverse_loop.PreCodegen.after.panic-unwind.mir
@@ -4,22 +4,22 @@ fn reverse_loop(_1: &[T], _2: impl Fn(&T)) -> () {
     debug slice => _1;
     debug f => _2;
     let mut _0: ();
-    let mut _12: std::slice::Iter<'_, T>;
+    let mut _11: std::slice::Iter<'_, T>;
+    let mut _12: std::iter::Rev<std::slice::Iter<'_, T>>;
     let mut _13: std::iter::Rev<std::slice::Iter<'_, T>>;
-    let mut _14: std::iter::Rev<std::slice::Iter<'_, T>>;
-    let mut _16: std::option::Option<&T>;
-    let mut _17: isize;
-    let mut _19: &impl Fn(&T);
-    let mut _20: (&T,);
-    let _21: ();
+    let mut _15: std::option::Option<&T>;
+    let mut _16: isize;
+    let mut _18: &impl Fn(&T);
+    let mut _19: (&T,);
+    let _20: ();
     scope 1 {
-        debug iter => _14;
-        let _18: &T;
+        debug iter => _13;
+        let _17: &T;
         scope 2 {
-            debug x => _18;
+            debug x => _17;
         }
         scope 17 (inlined <Rev<std::slice::Iter<'_, T>> as Iterator>::next) {
-            let mut _15: &mut std::slice::Iter<'_, T>;
+            let mut _14: &mut std::slice::Iter<'_, T>;
         }
     }
     scope 3 (inlined core::slice::<impl [T]>::iter) {
@@ -28,11 +28,10 @@ fn reverse_loop(_1: &[T], _2: impl Fn(&T)) -> () {
             let mut _7: bool;
             let mut _8: *mut T;
             let mut _9: *mut T;
-            let mut _11: *const T;
+            let mut _10: *const T;
             scope 5 {
                 let _6: std::ptr::NonNull<T>;
                 scope 6 {
-                    let _10: *const T;
                     scope 7 {
                     }
                     scope 11 (inlined without_provenance::<T>) {
@@ -61,16 +60,16 @@ fn reverse_loop(_1: &[T], _2: impl Fn(&T)) -> () {
     }
 
     bb0: {
-        StorageLive(_12);
+        StorageLive(_11);
         StorageLive(_3);
         StorageLive(_6);
+        StorageLive(_10);
         StorageLive(_4);
         StorageLive(_5);
         _3 = Len((*_1));
         _4 = &raw const (*_1);
         _5 = _4 as *const T (PtrToPtr);
         _6 = NonNull::<T> { pointer: _5 };
-        StorageLive(_10);
         StorageLive(_7);
         _7 = const <T as std::mem::SizedTypeProperties>::IS_ZST;
         switchInt(move _7) -> [0: bb1, otherwise: bb2];
@@ -94,38 +93,35 @@ fn reverse_loop(_1: &[T], _2: impl Fn(&T)) -> () {
 
     bb3: {
         StorageDead(_7);
-        StorageLive(_11);
-        _11 = _10;
-        _12 = std::slice::Iter::<'_, T> { ptr: _6, end_or_len: move _11, _marker: const ZeroSized: PhantomData<&T> };
-        StorageDead(_11);
-        StorageDead(_10);
+        _11 = std::slice::Iter::<'_, T> { ptr: _6, end_or_len: move _10, _marker: const ZeroSized: PhantomData<&T> };
         StorageDead(_5);
         StorageDead(_4);
+        StorageDead(_10);
         StorageDead(_6);
         StorageDead(_3);
-        _13 = Rev::<std::slice::Iter<'_, T>> { iter: _12 };
-        StorageDead(_12);
-        StorageLive(_14);
-        _14 = _13;
+        _12 = Rev::<std::slice::Iter<'_, T>> { iter: _11 };
+        StorageDead(_11);
+        StorageLive(_13);
+        _13 = _12;
         goto -> bb4;
     }
 
     bb4: {
-        StorageLive(_16);
         StorageLive(_15);
-        _15 = &mut (_14.0: std::slice::Iter<'_, T>);
-        _16 = <std::slice::Iter<'_, T> as DoubleEndedIterator>::next_back(move _15) -> [return: bb5, unwind: bb11];
+        StorageLive(_14);
+        _14 = &mut (_13.0: std::slice::Iter<'_, T>);
+        _15 = <std::slice::Iter<'_, T> as DoubleEndedIterator>::next_back(move _14) -> [return: bb5, unwind: bb11];
     }
 
     bb5: {
-        StorageDead(_15);
-        _17 = discriminant(_16);
-        switchInt(move _17) -> [0: bb6, 1: bb8, otherwise: bb10];
+        StorageDead(_14);
+        _16 = discriminant(_15);
+        switchInt(move _16) -> [0: bb6, 1: bb8, otherwise: bb10];
     }
 
     bb6: {
-        StorageDead(_16);
-        StorageDead(_14);
+        StorageDead(_15);
+        StorageDead(_13);
         drop(_2) -> [return: bb7, unwind continue];
     }
 
@@ -134,18 +130,18 @@ fn reverse_loop(_1: &[T], _2: impl Fn(&T)) -> () {
     }
 
     bb8: {
-        _18 = ((_16 as Some).0: &T);
+        _17 = ((_15 as Some).0: &T);
+        StorageLive(_18);
+        _18 = &_2;
         StorageLive(_19);
-        _19 = &_2;
-        StorageLive(_20);
-        _20 = (_18,);
-        _21 = <impl Fn(&T) as Fn<(&T,)>>::call(move _19, move _20) -> [return: bb9, unwind: bb11];
+        _19 = (_17,);
+        _20 = <impl Fn(&T) as Fn<(&T,)>>::call(move _18, move _19) -> [return: bb9, unwind: bb11];
     }
 
     bb9: {
-        StorageDead(_20);
         StorageDead(_19);
-        StorageDead(_16);
+        StorageDead(_18);
+        StorageDead(_15);
         goto -> bb4;
     }