[dmd-internals] Mixin forward reference semantic runs and field declarations

[Jason House]

Do you mean LDC should work around it? Or that it's something that should get fixed in the front end?

Sent from my iPhone

On Aug 30, 2012, at 9:39 PM, Walter Bright <walter at digitalmars.com> wrote:

> That looks like a compiler bug.
> 
> On 8/30/2012 4:00 PM, David Nadlinger wrote:
>> I am currently working on ironing out the last few kinks in the LDC
>> merge of the 2.060 frontend. The following snippet, a test case for
>> Bugzilla issue 7974, currently doesn't work with LDC:
>> 
>> ---
>> mixin template mix7974() {
>>   uint _x;
>> }
>> 
>> struct Foo7974 {
>>   immutable fa = Foo7974(0);
>> 
>>   this(uint x) {
>>     _x = x;
>>   }
>>   mixin mix7974!();
>> }
>> ---
>> 
>> The problem is that the fix Walter applied to the frontend for 7974
>> causes the semantic pass, including the arrayCopy() of the mixin
>> contents into the structs, to run twice, which leads to two separate
>> VarDeclarations for Foo7974._x being present at codegen time: one
>> instance, the one from the »forward reference« semantic run, is
>> referred to by the struct constructor, the other instance from the
>> second, »proper« run is e.g. what ends up in
>> StructDeclaration::fields.
>> 
>> As we tuck on IR construction metadata to field declarations in LDC,
>> having two instances for the same field breaks our codegen in
>> interesting ways – is this an unforeseen consequence of the fix in DMD
>> and  possibly a bug, or do I have to find a way to work around this in
>> LDC?
>> 
>> Thanks,
>> David
>> 
>> 
> 
> 
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