Add test.

tests/mir-opt/gvn_copy_moves.fn0.GVN.diff

@@ -0,0 +1,27 @@
+- // MIR for `fn0` before GVN
++ // MIR for `fn0` after GVN
+
+  fn fn0() -> () {
+      let mut _0: ();
+      let mut _1: usize;
+      let mut _2: [u128; 6];
+      let mut _3: ([u128; 6],);
+      let mut _4: ([u128; 6],);
+      let mut _5: ();
+
+      bb0: {
+          _1 = const 1_usize;
+          _2 = [const 42_u128; 6];
+-         _2[_1] = const 1_u128;
++         _2[1 of 2] = const 1_u128;
+          _3 = (_2,);
+          _4 = _3;
+-         _5 = fn1(move (_3.0: [u128; 6]), _4) -> [return: bb1, unwind unreachable];
++         _5 = fn1(move (_3.0: [u128; 6]), _3) -> [return: bb1, unwind unreachable];
+      }
+
+      bb1: {
+          return;
+      }
+  }
+

tests/mir-opt/gvn_copy_moves.rs

@@ -0,0 +1,46 @@
+// unit-test: GVN
+
+#![feature(custom_mir, core_intrinsics)]
+extern crate core;
+use core::intrinsics::mir::*;
+
+#[custom_mir(dialect = "runtime", phase = "initial")]
+fn fn0() {
+    // CHECK-LABEL: fn fn0(
+    mir! {
+        let a: usize;
+        let b: [u128; 6];
+        let c: ([u128; 6],);
+        let d: ([u128; 6],);
+        let x: ();
+        {
+            // CHECK: bb0: {
+            // CHECK-NEXT: _1 = const 1_usize;
+            // CHECK-NEXT: _2 = [const 42_u128; 6];
+            // CHECK-NEXT: _2[1 of 2] = const 1_u128;
+            // CHECK-NEXT: _3 = (_2,);
+            // CHECK-NEXT: _4 = _3;
+            // CHECK-NEXT: _5 = fn1((_3.0: [u128; 6]), _3)
+            a = 1_usize;
+            b = [42; 6];
+            b[a] = 1;
+            c = (b,);
+            d = c;
+            Call(x = fn1(Move(c.0), d), ReturnTo(bb1), UnwindUnreachable())
+        }
+        bb1 = {
+            Return()
+        }
+    }
+}
+
+#[inline(never)]
+fn fn1(a: [u128; 6], mut b: ([u128; 6],)) {
+    b.0 = [0; 6];
+}
+
+fn main() {
+    fn0();
+}
+
+// EMIT_MIR gvn_copy_moves.fn0.GVN.diff