# Visual Studio 2019 Compiler Hangs

(金庆的专栏 2021.7)

Discovered by my colleague Shen Yichai:
```
Share a interesting MS Build bug:
For file a.cpp, enable optimization for Win64 or XSX.
The MSBuild always compiling without error and ending (infinite compile).
The PS5 (clang) does not have this issue.
```

The simplified code:
```
struct Tag
{
    int v;
};

void Goo(Tag* r, Tag* a)
{
    r->v = a->v;
}

void Foo(Tag* pos0, Tag* pos)
{
    for (int j = 0; j < 4; j++)
    {
        if (j == 0) {
            for (int i = 0; i < 8; i++) {
                Goo(pos0++, pos);
                Goo(pos0++, pos);
            }
        }
        else {
            for (int i = 0; i < 8; i++) {
                Goo(pos0++, pos);
                Goo(pos0++, pos);
            }
        }
    }
}

int main()
{
    Foo(nullptr, nullptr);
}
```

The default release configuration can build correctly.
But if "Properties -> C/C++ -> Optimization -> Whole Program optimization" (/GL) of file or project is changed to "No",
the compilation will take a long time as 5 minutes.

```
Microsoft Visual Studio Community 2019
Version 16.9.5
VisualStudio.16.Release/16.9.5+31229.75
Microsoft .NET Framework
Version 4.8.04084
```