[LLVMdev] Inline hint for methods defined in-class

[Xinliang David Li]

that looks like a different fix. The case mentioned by Easwaran is

class A{
   int foo () { return 1; }
  ...
};

where 'foo' is not explicitly declared with 'inline' keyword.

David

On Wed, Jun 17, 2015 at 4:07 PM, Balaram Makam <bmakam at codeaurora.org> wrote:
> AFAIK, this was fixed in r233817.
>
> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On
> Behalf Of Easwaran Raman
> Sent: Wednesday, June 17, 2015 6:59 PM
> To: llvmdev at cs.uiuc.edu
> Cc: David Li
> Subject: [LLVMdev] Inline hint for methods defined in-class
>
> Clang adds the InlineHint attribute to functions that are explicitly marked
> inline, but not if they are defined in the class body. I tried the following
> patch, which I believe handles the in-class definition
> case:
>
> --- a/lib/CodeGen/CodeGenFunction.cpp
> +++ b/lib/CodeGen/CodeGenFunction.cpp
> @@ -630,7 +630,7 @@ void CodeGenFunction::StartFunction(GlobalDecl GD,
>    if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D)) {
>      if (!CGM.getCodeGenOpts().NoInline) {
>        for (auto RI : FD->redecls())
> -        if (RI->isInlineSpecified()) {
> +        if (RI->isInlined()) {
>            Fn->addFnAttr(llvm::Attribute::InlineHint);
>            break;
>          }
>
> I tried this on C++ benchmarks in SPEC 2006. There is no noticeable
> performance difference and the maximum text size increase is < 0.25%.
> I then built clang with and without this change. This increases the text
> size by 4.1%.  For measuring performance, I compiled a large (4.8 million
> lines) preprocessed file. This change improves runtime performance by 0.9%
> (average of 10 runs) in O0 and O2.
>
> I think knowing whether a function is defined inside a class body is a
> useful hint to the inliner. FWIW, GCC's inliner doesn't differentiate these
> from explicit inline functions. If the above results doesn't justify this
> change, are there other benchmarks that I should evaluate? Another
> possibility is to add a separate hint for this instead of using the existing
> inlinehint to allow for better tuning in the inliner.
>
> Thanks,
> Easwaran
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