do not merge(perf): reduce llvm stress

by not make llvm de-duplicates arrays between promote temp pass and gvn.

Author: tesuji

compiler/rustc_mir_transform/src/gvn.rs

@@ -1451,6 +1451,15 @@ impl<'tcx> VnState<'_, 'tcx> {
 
         let op = self.evaluated[index].as_ref()?;
 
+        // Ignore promoted arrays. Promoted arrays are already placed in `.rodata`.
+        // Which is what we try to archive for running gvn on constant local arrays.
+        if let Either::Left(mplace) = op.as_mplace_or_imm()
+            && mplace.layout.ty.is_array()
+            && let Value::Projection(_index, ProjectionElem::Deref) = self.get(index)
+        {
+            return None;
+        }
+
         let value = op_to_prop_const(&mut self.ecx, op)?;
 
         // Check that we do not leak a pointer.

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

@@ -59,7 +59,7 @@
           _17 = const main::promoted[0];
           _7 = &(*_17);
 -         _6 = (*_7);
-+         _6 = const [254_i32, 42_i32, 15_i32, 39_i32, 62_i32];
++         _6 = (*_17);
           StorageDead(_7);
           StorageLive(_9);
           StorageLive(_10);
@@ -124,6 +124,4 @@
 + ALLOC8 (size: 20, align: 4) { .. }
 + 
 + ALLOC9 (size: 20, align: 4) { .. }
-+ 
-+ ALLOC10 (size: 20, align: 4) { .. }
 

tests/mir-opt/const_array_locals.rs

@@ -22,7 +22,7 @@ pub fn main() {
     // CHECK{LITERAL}: const [[178_i32, 9_i32, 4_i32, 56_i32, 221_i32], [193_i32, 164_i32, 194_i32, 197_i32, 6_i32]];
     let _foo = [[178, 9, 4, 56, 221], [193, 164, 194, 197, 6]];
     // CHECK: [[PROMOTED:_[0-9]+]] = const main::promoted[0];
-    // CHECK: [[_darr]] = const [254_i32, 42_i32, 15_i32, 39_i32, 62_i32];
+    // CHECK: [[_darr]] = (*[[PROMOTED]]);
     let _darr = *&[254, 42, 15, 39, 62];
 
     // CHECK: [[ARG:_[0-9]+]] = const [31_u32, 96_u32, 173_u32, 50_u32, 1_u32];