harec

commit d4bd9749de1ea29690b9f9d4d9c6a04c69da05bc
parent 1ee3a9573c990bc15544be8cbcb7ca2879c439cb
Author: Drew DeVault <sir@cmpwn.com>
Date:   Thu,  5 Aug 2021 15:44:56 +0200

gen: implement subtype tagged casts

Just one of two cases is implemented here; the second requires more
work.

Signed-off-by: Drew DeVault <sir@cmpwn.com>

Diffstat:
M
src/gen.c
 | 
21
++++++++++++++++++---
M
tests/910-tagged.ha
 | 
23
++++++++++++++++++++---

2 files changed, 38 insertions(+), 6 deletions(-)
diff --git a/src/gen.c b/src/gen.c
@@ -124,7 +124,9 @@ gen_store(struct gen_context *ctx,
 		gen_copy_aligned(ctx, object, value);
 		return;
 	case STORAGE_TAGGED:
-		assert(0); // TODO
+		// TODO: We can be smarter in this case
+		gen_copy_aligned(ctx, object, value);
+		return;
 	case STORAGE_UNION:
 		gen_copy_memcpy(ctx, object, value);
 		return;
@@ -463,10 +465,23 @@ gen_expr_cast_at(struct gen_context *ctx,
 		return;
 	}
 
-	// Cast to tagged union
 	const struct type *subtype = tagged_select_subtype(to, from);
-	assert(subtype); // TODO: Casting between incompatible tagged unions
+	assert(subtype || tagged_subset_compat(to, from));
+	if (!subtype && to->align == from->align) {
+		// Case 1: from is a union whose members are a subset of to, and
+		// the alignment matches, so we can just interpret values of
+		// type 'from' as if it were of type 'to'
+		struct gen_value out2 = out;
+		out2.type = from;
+		gen_expr_at(ctx, expr->cast.value, out2);
+		return;
+	} else if (!subtype) {
+		// Case 2: alignment mismatch, so (much) more work is required.
+		assert(0); // TODO
+		return;
+	}
 
+	// Case 3: from is a member of to
 	struct qbe_value qout = mkqval(ctx, &out);
 	struct qbe_value id = constw(subtype->id);
 	enum qbe_instr store = store_for_type(ctx, &builtin_type_uint);
diff --git a/tests/910-tagged.ha b/tests/910-tagged.ha
@@ -1,4 +1,4 @@
-fn totagged() void = {
+fn membercast() void = {
 	// Simple case
 	let x: (int | void) = void;
 	let p = &x: *struct {
@@ -33,11 +33,28 @@ fn totagged() void = {
 	};
 	assert(p.id == 4119164483);
 	assert(p.data == 1337z);
+};
+
+fn subsetcast() void = {
+	// Equal alignment
+	let x: (size | void) = 1337z;
+	let y: (size | int | void) = x;
+	let p = &y: *struct {
+		tag: uint,
+		data: union {
+			z: size,
+			i: int,
+		},
+	};
+	assert(p.tag == 4119164483);
+	assert(p.data.z == 1337z);
 
-	// TODO: More cases
+	// Disjoint alignment
+	// TODO
 };
 
 export fn main() int = {
-	totagged();
+	membercast();
+	subsetcast();
 	return 0;
 };