• d-bugmail puremagic.com (50/50) May 15 2020 https://issues.dlang.org/show_bug.cgi?id=20834

d-bugmail puremagic.com writes:

https://issues.dlang.org/show_bug.cgi?id=20834

          Issue ID: 20834
           Summary: pragma(inline, true) fails to inline simple functions.
                    fails with -inline
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: major
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: witold.baryluk+d gmail.com

https://godbolt.org/z/keEyMi

```
private final struct PTest {
  ulong j;

  pragma(inline, true)
  final bool f() {
    return !(j & 0xfffffffuL);  // Works.
  }

  pragma(inline, true)
  final bool g() {
    // Doesn't work in DMD.
    if (!(j & 0xfffffffuL)) {
        j++;
      return true;
    } else {
      return false;
    }
  }
}

void test1() {
  scope p = PTest();
  p.f();
  p.g();
}
```

this fail to compile when using `dmd -O -inline`.

:(

1) DMD should be a bit smarter and consider more function types for inlining.
It looks like right now it only consider `return (expr);`-style functions only.

2) There should be a switch to dmd compiler, or different pragma, to not make
it an error, but just a warning. `pragma(hint_inline, true)` maybe?

I noticed this problem, when I tried to move some of the code into struct on
stack and call to its methods, but saw 20% performance drop. assembly revealed
missing inlining to one of the function. trying to inline it with pragma failed
as above.

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