[PATCH] Fix for inlining decision affected by debug intrinsics

[Manman Ren]

LGTM. Thanks for the detailed comments.

I noticed a few debugging-related changes, it may be better to separate
those.
+  DEBUG_PRINT_STAT(Cost);
+  DEBUG_PRINT_STAT(Threshold);
+  DEBUG_PRINT_STAT(VectorBonus);

Manman


On Fri, Jan 31, 2014 at 10:55 AM, Dario Domizioli <dario.domizioli at gmail.com
> wrote:

> Hello LLVM.
>
> I have come across a subtle and rare interaction between debug
> information, vector instructions, and the cost heuristic used by the
> SimpleInliner (i.e. the InlineCost analysis).
>
> It appears that debug intrinsics are counted in the number of instructions
> taken into consideration by the heuristic. They are also later discounted
> as being "simplified", so they do not directly affect the inline Cost, but
> they are taken into account when evaluating the fraction of instructions
> that are vector instructions. This fraction is used to determine whether to
> apply a hidden "VectorBonus" to the inlining Threshold, and therefore there
> is a subtle interaction which means that debug intrinsics can affect the
> inlining decision.
>
> The attached patch fixes the problem by making the inline cost heuristic
> skip debug intrinsics altogether when examining instructions.
> I have also added a couple of debug prints to the already existing ones,
> which I think are generally useful to debug the inline cost heuristic.
>
> I have included a test in which I have manufactured a situation where
> vector instructions would be most of the function's code but they are
> outnumbered by debug intrinsics when debug information is present. The test
> exposes the problem in the current trunk and passes with my fix.
>
> Please submit for me if you accept this patch, as I do not have commit
> access.
>
> Cheers,
>     Dario Domizioli
>     SN Systems - Sony Computer Entertainment
>
>
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>
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