[PATCH] D79526: [CUDA][HIP] Workaround for resolving host device function against wrong-sided function

[Yaxun Liu via Phabricator via cfe-commits]

yaxunl added a comment.

In D79526#2042680 <https://reviews.llvm.org/D79526#2042680>, @tra wrote:

> Reduced test case:
>
>   struct a {
>     __attribute__((device)) a(short);
>     __attribute__((device)) operator unsigned() const;
>     __attribute__((device)) operator int() const;
>   };
>   struct b {
>     a d;
>   };
>   void f(b g) { b e = g; }
>
>
> Failure:
>
>   $ bin/clang++ -x cuda aten.cc -fsyntax-only  --cuda-path=$HOME/local/cuda-10.1 --cuda-device-only --cuda-gpu-arch=sm_60 -stdlib=libc++ -std=c++17 -ferror-limit=1
>  
>   aten.cc:6:8: error: conversion from 'const a' to 'short' is ambiguous
>   struct b {
>          ^
>   aten.cc:9:21: note: in implicit copy constructor for 'b' first required here
>   void f(b g) { b e = g; }
>                       ^
>   aten.cc:3:27: note: candidate function
>     __attribute__((device)) operator unsigned() const;
>                             ^
>   aten.cc:4:27: note: candidate function
>     __attribute__((device)) operator int() const;
>                             ^
>   aten.cc:2:34: note: passing argument to parameter here
>     __attribute__((device)) a(short);
>                                    ^
>   1 error generated when compiling for sm_60.
>
>
> The same code compiles fine in C++ and I would expect it to work on device side the same way.


a and b both have an implicit HD copy ctor. In device compilation, copy ctor of b is calling copy ctor of a. There are two candidates: implicit HD copy ctor of a, and device ctor a(short).

In my previous fix, I made H and implicit HD candidate equal, however I forgot about the relation between D candidate and HD candidate. I incorrectly made D favored over HD and H. This caused inferior device candidate a(short) chosen over copy ctor of a.

I have a fix for this https://reviews.llvm.org/D80450


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