Let LLVM de-duplicates arrays has same value

Author: tesuji

compiler/rustc_mir_transform/src/gvn.rs

@@ -1539,17 +1539,7 @@ impl<'tcx> MutVisitor<'tcx> for VnState<'_, 'tcx> {
                 .or_else(|| self.simplify_rvalue(rvalue, location));
             let Some(value) = value else { return };
 
-            // De-duplicate locals has the same arrays assigned to prevent code bloat.
-            let disallowed_duplicated_array = if rvalue.ty(self.local_decls, self.tcx).is_array()
-                && let Some(locals) = self.rev_locals.get(value).as_deref()
-                && let [first, ..] = locals[..]
-            {
-                first != lhs.local
-            } else {
-                false
-            };
-
-            if !disallowed_duplicated_array && let Some(const_) = self.try_as_constant(value) {
+            if let Some(const_) = self.try_as_constant(value) {
                 *rvalue = Rvalue::Use(Operand::Constant(Box::new(const_)));
             } else if let Some(local) = self.try_as_local(value, location)
                 && *rvalue != Rvalue::Use(Operand::Move(local.into()))

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

@@ -37,13 +37,12 @@
       }
 
       bb0: {
--         StorageLive(_1);
+          StorageLive(_1);
 -         _1 = [const 255_i32, const 105_i32, const 15_i32, const 39_i32, const 62_i32];
-+         nop;
 +         _1 = const [255_i32, 105_i32, 15_i32, 39_i32, 62_i32];
           StorageLive(_2);
 -         _2 = [const 255_i32, const 105_i32, const 15_i32, const 39_i32, const 62_i32];
-+         _2 = _1;
++         _2 = const [255_i32, 105_i32, 15_i32, 39_i32, 62_i32];
           StorageLive(_3);
           StorageLive(_4);
 -         _4 = [const 178_i32, const 9_i32, const 4_i32, const 56_i32, const 221_i32];
@@ -94,8 +93,7 @@
           StorageDead(_6);
           StorageDead(_3);
           StorageDead(_2);
--         StorageDead(_1);
-+         nop;
+          StorageDead(_1);
           return;
       }
 + }

tests/mir-opt/const_array_locals.rs

@@ -14,7 +14,7 @@ struct F32x8([f32; 8]);
 pub fn main() {
     // CHECK: [[_arr]] = const [255_i32, 105_i32, 15_i32, 39_i32, 62_i32];
     let _arr = [255, 105, 15, 39, 62];
-    // CHECK: [[_duplicated_arr]] = [[_arr]];
+    // CHECK: [[_duplicated_arr]] = const [255_i32, 105_i32, 15_i32, 39_i32, 62_i32];
     let _duplicated_arr = [255, 105, 15, 39, 62];
     // CHECK: [[subarray1:_[0-9]+]] = const [178_i32, 9_i32, 4_i32, 56_i32, 221_i32];
     // CHECK: [[subarray2:_[0-9]+]] = const [193_i32, 164_i32, 194_i32, 197_i32, 6_i32];