Attempt to improve codegen for arrays of repeated enums

compiler/rustc_codegen_llvm/src/builder.rs

@@ -561,6 +561,24 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         count: u64,
         dest: PlaceRef<'tcx, &'ll Value>,
     ) -> Self {
+        if let OperandValue::Pair(mut v1, mut v2) = cg_elem.val && count < 1024 {
+            v1 = self.from_immediate(v1);
+            v2 = self.from_immediate(v2);
+            let ty = self.cx().val_ty(v1);
+            // Create a vector of size 2*count and store it in one instruction
+            if ty == self.cx().val_ty(v2) {
+                let count = count * 2;
+                let vec = unsafe { llvm::LLVMGetUndef(self.type_vector(ty, count as u64)) };
+                let vec = (0..count as usize).fold(vec, |acc, x| {
+                    let elt = [v1, v2][x % 2];
+                    self.insert_element(acc, elt, self.cx.const_i32(x as i32))
+                });
+                let vec = OperandRef::from_immediate_or_packed_pair(&mut self, vec, dest.layout);
+                vec.val.store(&mut self, dest);
+                return self;
+            }
+        }
+
         let zero = self.const_usize(0);
         let count = self.const_usize(count);
         let start = dest.project_index(&mut self, zero).llval;

compiler/rustc_codegen_ssa/src/mir/operand.rs

@@ -12,8 +12,6 @@ use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
 use rustc_middle::ty::Ty;
 use rustc_target::abi::{Abi, Align, Size};
 
-use std::fmt;
-
 /// The representation of a Rust value. The enum variant is in fact
 /// uniquely determined by the value's type, but is kept as a
 /// safety check.
@@ -38,7 +36,7 @@ pub enum OperandValue<V> {
 /// to avoid nasty edge cases. In particular, using `Builder::store`
 /// directly is sure to cause problems -- use `OperandRef::store`
 /// instead.
-#[derive(Copy, Clone)]
+#[derive(Copy, Clone, Debug)]
 pub struct OperandRef<'tcx, V> {
     // The value.
     pub val: OperandValue<V>,
@@ -47,12 +45,6 @@ pub struct OperandRef<'tcx, V> {
     pub layout: TyAndLayout<'tcx>,
 }
 
-impl<V: CodegenObject> fmt::Debug for OperandRef<'_, V> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "OperandRef({:?} @ {:?})", self.val, self.layout)
-    }
-}
-
 impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
     pub fn new_zst<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
         bx: &mut Bx,

src/test/codegen/enum-repeat.rs

@@ -0,0 +1,19 @@
+// compile-flags: -O
+
+#![crate_type = "lib"]
+
+// CHECK-LABEL: @none_repeat
+#[no_mangle]
+pub fn none_repeat() -> [Option<u8>; 64] {
+    // CHECK: store <128 x i8>
+    // CHECK-NEXT: ret void
+    [None; 64]
+}
+
+// CHECK-LABEL: @some_repeat
+#[no_mangle]
+pub fn some_repeat() -> [Option<u8>; 64] {
+    // CHECK: store <128 x i8>
+    // CHECK-NEXT: ret void
+    [Some(0); 64]
+}