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LLVM: fix lowering of untagged union types

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The LLVM backend was calculating the amount of padding solely based
on the payload size. However, in the case where there is no union
tag, this fails to take into account alignment.

Closes #11857
This commit is contained in:
Andrew Kelley
2022-06-29 19:01:48 -07:00
parent 54454fd010
commit c248af3bdc
3 changed files with 24 additions and 5 deletions
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7
src/codegen/llvm.zig
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@@ -2708,7 +2708,10 @@ pub const DeclGen = struct {
if (layout.most_aligned_field_size == layout.payload_size) {
break :t llvm_aligned_field_ty;
}
const padding_len = @intCast(c_uint, layout.payload_size - layout.most_aligned_field_size);
const padding_len = if (layout.tag_size == 0)
@intCast(c_uint, layout.abi_size - layout.most_aligned_field_size)
else
@intCast(c_uint, layout.payload_size - layout.most_aligned_field_size);
const fields: [2]*const llvm.Type = .{
llvm_aligned_field_ty,
dg.context.intType(8).arrayType(padding_len),
@@ -5756,7 +5759,7 @@ pub const FuncGen = struct {
// First set the non-null bit.
const indices: [2]*const llvm.Value = .{
index_type.constNull(), // dereference the pointer
index_type.constInt(1, .False), // second field is the payload
index_type.constInt(1, .False), // second field is the non-null bit
};
const non_null_ptr = self.builder.buildInBoundsGEP(operand, &indices, indices.len, "");
_ = self.builder.buildStore(non_null_bit, non_null_ptr);