Simplify repeat expressions.

Author: cjgillot

compiler/rustc_mir_transform/src/gvn.rs

@@ -499,11 +499,17 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                 ProjectionElem::Field(f, ty)
             }
             ProjectionElem::Index(idx) => {
+                if let Value::Repeat(inner, _) = self.get(value) {
+                    return Some(*inner);
+                }
                 let idx = self.locals[idx]?;
                 ProjectionElem::Index(idx)
             }
             ProjectionElem::ConstantIndex { offset, min_length, from_end } => {
                 match self.get(value) {
+                    Value::Repeat(inner, _) => {
+                        return Some(*inner);
+                    }
                     Value::Aggregate(ty, _, operands) if ty.is_array() => {
                         let offset = if from_end {
                             operands.len() - offset as usize

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

@@ -41,8 +41,9 @@
 
       bb1: {
 -         _6 = _3[_7];
-+         _6 = _3[0 of 1];
-          _5 = opaque::<T>(move _6) -> [return: bb2, unwind unreachable];
+-         _5 = opaque::<T>(move _6) -> [return: bb2, unwind unreachable];
++         _6 = _1;
++         _5 = opaque::<T>(_1) -> [return: bb2, unwind unreachable];
       }
 
       bb2: {
@@ -63,8 +64,9 @@
 
       bb3: {
 -         _11 = _3[_12];
-+         _11 = _3[_2];
-          _10 = opaque::<T>(move _11) -> [return: bb4, unwind unreachable];
+-         _10 = opaque::<T>(move _11) -> [return: bb4, unwind unreachable];
++         _11 = _1;
++         _10 = opaque::<T>(_1) -> [return: bb4, unwind unreachable];
       }
 
       bb4: {

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

@@ -41,8 +41,9 @@
 
       bb1: {
 -         _6 = _3[_7];
-+         _6 = _3[0 of 1];
-          _5 = opaque::<T>(move _6) -> [return: bb2, unwind continue];
+-         _5 = opaque::<T>(move _6) -> [return: bb2, unwind continue];
++         _6 = _1;
++         _5 = opaque::<T>(_1) -> [return: bb2, unwind continue];
       }
 
       bb2: {
@@ -63,8 +64,9 @@
 
       bb3: {
 -         _11 = _3[_12];
-+         _11 = _3[_2];
-          _10 = opaque::<T>(move _11) -> [return: bb4, unwind continue];
+-         _10 = opaque::<T>(move _11) -> [return: bb4, unwind continue];
++         _11 = _1;
++         _10 = opaque::<T>(_1) -> [return: bb4, unwind continue];
       }
 
       bb4: {