stage2: fixes for error unions, optionals, errors

 * `?E` where E is an error set with only one field now lowers the same
   as `bool`.
 * Fix implementation of errUnionErrOffset and errUnionPayloadOffset to
   properly compute the offset of each field. Also name them the same
   as the corresponding LLVM functions and have the same function
   signature, to avoid confusion. This fixes a bug where wasm was
   passing the error union type instead of the payload type.
 * Fix C backend handling of optionals with zero-bit payload types.
 * C backend: separate out airOptionalPayload and airOptionalPayloadPtr
   which reduces branching and cleans up control flow.
 * Make Type.isNoReturn return true for error sets with no fields.
 * Make `?error{}` have only one possible value (null).

1 files changed, 16 insertions, 12 deletions

diff --git a/src/codegen.zig b/src/codegen.zig
index 86f2613b5f..fbe462959e 100644
--- a/src/codegen.zig
+++ b/src/codegen.zig
@@ -891,18 +891,22 @@ fn lowerDeclRef(
     return Result{ .appended = {} };
 }
 
-pub fn errUnionPayloadOffset(ty: Type, target: std.Target) u64 {
-    const payload_ty = ty.errorUnionPayload();
-    return if (Type.anyerror.abiAlignment(target) >= payload_ty.abiAlignment(target))
-        Type.anyerror.abiSize(target)
-    else
-        0;
+pub fn errUnionPayloadOffset(payload_ty: Type, target: std.Target) u64 {
+    const payload_align = payload_ty.abiAlignment(target);
+    const error_align = Type.anyerror.abiAlignment(target);
+    if (payload_align >= error_align) {
+        return 0;
+    } else {
+        return mem.alignForwardGeneric(u64, Type.anyerror.abiSize(target), payload_align);
+    }
 }
 
-pub fn errUnionErrOffset(ty: Type, target: std.Target) u64 {
-    const payload_ty = ty.errorUnionPayload();
-    return if (Type.anyerror.abiAlignment(target) >= payload_ty.abiAlignment(target))
-        0
-    else
-        payload_ty.abiSize(target);
+pub fn errUnionErrorOffset(payload_ty: Type, target: std.Target) u64 {
+    const payload_align = payload_ty.abiAlignment(target);
+    const error_align = Type.anyerror.abiAlignment(target);
+    if (payload_align >= error_align) {
+        return mem.alignForwardGeneric(u64, payload_ty.abiSize(target), error_align);
+    } else {
+        return 0;
+    }
 }