handle vector layout

Author: erikdesjardins

compiler/rustc_codegen_ssa/src/mir/place.rs

@@ -96,7 +96,7 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
             let llval = match self.layout.abi {
                 _ if offset.bytes() == 0 => {
                     // Unions and newtypes only use an offset of 0.
-                    // Also handles the first field of Scalar and ScalarPair layouts.
+                    // Also handles the first field of Scalar, ScalarPair, and Vector layouts.
                     self.llval
                 }
                 Abi::ScalarPair(ref a, ref b)
@@ -105,16 +105,20 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
                     // Offset matches second field.
                     bx.struct_gep(self.llval, 1)
                 }
-                Abi::ScalarPair(..) | Abi::Scalar(_) => {
-                    // ZST fields are not included in Scalar and ScalarPair layouts, so manually offset the pointer.
-                    assert!(
-                        field.is_zst(),
-                        "non-ZST field offset does not match layout: {:?}",
-                        field
-                    );
+                Abi::Scalar(_) | Abi::ScalarPair(..) | Abi::Vector { .. } if field.is_zst() => {
+                    // ZST fields are not included in Scalar, ScalarPair, and Vector layouts, so manually offset the pointer.
                     let byte_ptr = bx.pointercast(self.llval, bx.cx().type_i8p());
                     bx.gep(byte_ptr, &[bx.const_usize(offset.bytes())])
                 }
+                Abi::Scalar(_) | Abi::ScalarPair(..) => {
+                    // All fields of Scalar and ScalarPair layouts must have been handled by this point.
+                    // Vector layouts have additional fields for each element of the vector, so don't panic in that case.
+                    bug!(
+                        "offset of non-ZST field `{:?}` does not match layout `{:#?}`",
+                        field,
+                        self.layout
+                    );
+                }
                 _ => bx.struct_gep(self.llval, bx.cx().backend_field_index(self.layout, ix)),
             };
             PlaceRef {

src/test/codegen/zst-offset.rs

@@ -1,6 +1,7 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type = "lib"]
+#![feature(repr_simd)]
 
 // Hack to get the correct size for the length part in slices
 // CHECK: @helper([[USIZE:i[0-9]+]] %_1)
@@ -27,3 +28,16 @@ pub fn scalarpair_layout(s: &(u64, u32, ())) {
     let x = &s.2;
     &x; // keep variable in an alloca
 }
+
+#[repr(simd)]
+pub struct U64x4(u64, u64, u64, u64);
+
+// Check that we correctly generate a GEP for a ZST that is not included in Vector layout
+// CHECK-LABEL: @vector_layout
+#[no_mangle]
+pub fn vector_layout(s: &(U64x4, ())) {
+// CHECK: [[X0:%[0-9]+]] = bitcast <4 x i64>* %s to i8*
+// CHECK-NEXT: [[X1:%[0-9]+]] = getelementptr i8, i8* [[X0]], [[USIZE]] 32
+    let x = &s.1;
+    &x; // keep variable in an alloca
+}