Auto merge of #144477 - cjgillot:gvn-index, r=dianqk

GVN: Use a VnIndex in Address projection.

The current implementation of address projections is inconsistent. Indexing semantically relies on the index' value, but the implementation uses the index' place. This PR fixes that by using `ProjectionElem<VnIndex, Ty<'tcx>>` instead of the raw `PlaceElem<'tcx>`.

This is a more principled fix than the workaround in #145030.

Author: bors

compiler/rustc_mir_transform/src/gvn.rs

@@ -43,7 +43,8 @@
 +         nop;
           StorageLive(_8);
           StorageLive(_9);
-          _9 = copy (*_3);
+-         _9 = copy (*_3);
++         _9 = copy _1[_4];
           _8 = opaque::<u8>(move _9) -> [return: bb2, unwind unreachable];
       }
 

tests/mir-opt/gvn.dereference_indexing.GVN.panic-abort.diff

@@ -43,7 +43,8 @@
 +         nop;
           StorageLive(_8);
           StorageLive(_9);
-          _9 = copy (*_3);
+-         _9 = copy (*_3);
++         _9 = copy _1[_4];
           _8 = opaque::<u8>(move _9) -> [return: bb2, unwind continue];
       }
 

tests/mir-opt/gvn.dereference_indexing.GVN.panic-unwind.diff

@@ -1065,8 +1065,8 @@ fn dereference_indexing(array: [u8; 2], index: usize) {
         &array[i]
     };
 
-    // CHECK-NOT: [{{.*}}]
-    // CHECK: [[tmp:_.*]] = copy (*[[a]]);
+    // CHECK-NOT: StorageDead([[i]]);
+    // CHECK: [[tmp:_.*]] = copy _1[[[i]]];
     // CHECK: opaque::<u8>(move [[tmp]])
     opaque(*a);
 }

tests/mir-opt/gvn.rs

@@ -0,0 +1,15 @@
+- // MIR for `index_place` before GVN
++ // MIR for `index_place` after GVN
+  
+  fn index_place(_1: usize, _2: usize, _3: [i32; 5]) -> i32 {
+      let mut _0: i32;
+      let mut _4: &i32;
+  
+      bb0: {
+          _4 = &_3[_1];
+          _1 = copy _2;
+          _0 = copy (*_4);
+          return;
+      }
+  }
+  

tests/mir-opt/gvn_repeat.index_place.GVN.diff

@@ -10,8 +10,7 @@
           _4 = [copy _3; 5];
           _5 = &_4[_1];
           _1 = copy _2;
--         _0 = copy (*_5);
-+         _0 = copy _3;
+          _0 = copy (*_5);
           return;
       }
   }

tests/mir-opt/gvn_repeat.repeat_local.GVN.diff

@@ -6,6 +6,23 @@
 
 use std::intrinsics::mir::*;
 
+// EMIT_MIR gvn_repeat.index_place.GVN.diff
+#[custom_mir(dialect = "runtime")]
+pub fn index_place(mut idx1: usize, idx2: usize, array: [i32; 5]) -> i32 {
+    // CHECK-LABEL: fn index_place(
+    // CHECK: let mut [[ELEM:.*]]: &i32;
+    // CHECK: _0 = copy (*[[ELEM]])
+    mir! {
+        let elem;
+        {
+            elem = &array[idx1];
+            idx1 = idx2;
+            RET = *elem;
+            Return()
+        }
+    }
+}
+
 // EMIT_MIR gvn_repeat.repeat_place.GVN.diff
 #[custom_mir(dialect = "runtime")]
 pub fn repeat_place(mut idx1: usize, idx2: usize, val: &i32) -> i32 {
@@ -29,7 +46,8 @@ pub fn repeat_place(mut idx1: usize, idx2: usize, val: &i32) -> i32 {
 #[custom_mir(dialect = "runtime")]
 pub fn repeat_local(mut idx1: usize, idx2: usize, val: i32) -> i32 {
     // CHECK-LABEL: fn repeat_local(
-    // CHECK: _0 = copy _3
+    // CHECK: let mut [[ELEM:.*]]: &i32;
+    // CHECK: _0 = copy (*[[ELEM]]);
     mir! {
         let array;
         let elem;
@@ -44,6 +62,7 @@ pub fn repeat_local(mut idx1: usize, idx2: usize, val: i32) -> i32 {
 }
 
 fn main() {
+    assert_eq!(index_place(0, 5, [0; 5]), 0);
     assert_eq!(repeat_place(0, 5, &0), 0);
     assert_eq!(repeat_local(0, 5, 0), 0);
 }