www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.bugs - [Issue 20834] New: pragma(inline, true) fails to inline simple


          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


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)) {
      return true;
    } else {
      return false;

void test1() {
  scope p = PTest();

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.

May 15 2020