really ignore nested arrays

Author: tesuji

compiler/rustc_mir_transform/src/gvn.rs

@@ -927,8 +927,12 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
         }
 
         let (mut ty, variant_index) = match *kind {
-            AggregateKind::Array(..) => {
+            AggregateKind::Array(ty) => {
                 assert!(!field_ops.is_empty());
+                // Ignore nested arrays
+                if ty.is_array() {
+                    return None;
+                }
                 (AggregateTy::Array, FIRST_VARIANT)
             }
             AggregateKind::Tuple => {
@@ -1501,17 +1505,12 @@ impl<'tcx> VnState<'_, 'tcx> {
 
         let op = self.evaluated[index].as_ref()?;
 
+        // Ignore promoted arrays.
         if let Either::Left(mplace) = op.as_mplace_or_imm()
-            && let ty::Array(ty, _const) = mplace.layout.ty.kind()
+            && mplace.layout.ty.is_array()
+            && let Value::Projection(_index, ProjectionElem::Deref) = value
         {
-            // ignore nested arrays
-            if ty.is_array() {
-                return None;
-            }
-            // ignore promoted arrays
-            else if let Value::Projection(_index, ProjectionElem::Deref) = value {
-                return None;
-            }
+            return None;
         }
 
         let value = op_to_prop_const(&mut self.ecx, op)?;

tests/mir-opt/const_array_locals.main.GVN.diff

@@ -49,9 +49,8 @@
 +         _4 = const [255_i32, 105_i32, 15_i32, 39_i32, 62_i32, 251_i32, 191_i32, 178_i32, 9_i32, 4_i32, 56_i32, 221_i32];
           StorageLive(_5);
 -         _5 = [const 193_i32, const 164_i32, const 194_i32, const 197_i32, const 6_i32, const 243_i32, const 218_i32, const 171_i32, const 87_i32, const 247_i32, const 104_i32, const 42_i32];
--         _3 = [move _4, move _5];
 +         _5 = const [193_i32, 164_i32, 194_i32, 197_i32, 6_i32, 243_i32, 218_i32, 171_i32, 87_i32, 247_i32, 104_i32, 42_i32];
-+         _3 = [const [255_i32, 105_i32, 15_i32, 39_i32, 62_i32, 251_i32, 191_i32, 178_i32, 9_i32, 4_i32, 56_i32, 221_i32], const [193_i32, 164_i32, 194_i32, 197_i32, 6_i32, 243_i32, 218_i32, 171_i32, 87_i32, 247_i32, 104_i32, 42_i32]];
+          _3 = [move _4, move _5];
           StorageDead(_5);
           StorageDead(_4);
           StorageLive(_6);