[REG 2.077] Type merging immutable -> mutable broken in AST

[dlangBugzillaToGithub]

Iain Buclaw (@ibuclaw) reported this on 2018-06-24T14:19:16Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=19021

CC List

• Iain Buclaw (@ibuclaw)

Description

Commit that caused regression.

https://github.com/dlang/dmd/pull/6998/commits/46b0f6b9a2a089ed6dcd106ca03fc7b2e040385d#diff-33cd340a268c63317687a0a372cd3d94L403


It happen that there are two mutable types T that have different deco, but point to the same immutable!T because of failure to recognize that T and T are the same type.

---
struct MultiwayMerge()
{ 
    bool compFront()
    {
        return true;
    }

    struct BinaryHeap(alias less)
    {
        struct Impl
        {
            int _payload;
        }

        void initialize()
        {
            immutable Impl init;
            checkTypes(init);
        }

        void checkTypes(T)(immutable T init)
        {
            alias IT = typeof(init);    // immutable(Impl)
            alias MT = T;               // Impl
            static assert(MT.mangleof == "S6setops__T13MultiwayMergeZQq__T10BinaryHeapS_DQBu__TQBqZQBu9compFrontMFNaNbNiNfZbZQBz4Impl");
            static assert(IT.mangleof == "yS6setops__T13MultiwayMergeZQq__T10BinaryHeapS_DQBu__TQBqZQBu9compFrontMFNaNbNiNfZbZQBz4Impl");
        }

        // Should be same as MT
        static assert(Impl.mangleof == "S6setops__T13MultiwayMergeZQq__T10BinaryHeapS_DQBu__TQBqZQBu9compFrontMFNaNbNiNfZbZQBz4Impl");
    }

    BinaryHeap!(compFront) _heap;
}

MultiwayMerge!() multiwayMerge;

---


What looks to be the case is that mangleToBuffer is called before compFront has finished its semantic, so the first mutable T does not have pure nothrow @nogc encoded into its symbol.

[dlangBugzillaToGithub]

ibuclaw (@ibuclaw) commented on 2018-06-24T14:21:25Z

Commit looks related https://github.com/dlang/dmd/commit/2c0ead859f208d80190d4e634b5a0737d4b64645

Introduced adding a link between `shared(T)`, `inout(T)` and `const(T)` with `T`.  But left out `immutable(T)` despite this comment here that seems to suggest that there should be one.

https://github.com/dlang/dmd/commit/2c0ead859f208d80190d4e634b5a0737d4b64645#diff-ffafa03255a57832dd09031af6cb915dR470

[dlangBugzillaToGithub]

ibuclaw (@ibuclaw) commented on 2018-06-24T14:24:48Z

Adding in the reference fixes immediate bug.

https://github.com/dlang/dmd/pull/8398


But now `pure nothrow @nogc` is no longer part of the symbol mangle.

[dlangBugzillaToGithub]

ibuclaw (@ibuclaw) commented on 2018-06-24T16:12:27Z

Blocking GDC, as there's an ICE in the glue/back-end.

Said ICE is valid, the problem is in the front-end.