[LLVMdev] Inlining into a big function
Chris Lattner
clattner at apple.com
Mon Mar 8 20:28:53 PST 2010
On Mar 8, 2010, at 7:17 PM, Jakob Stoklund Olesen wrote:
> Hi,
>
> The InlineCostAnalyzer has contained this since it was created:
>
> + // Don't inline into something too big, which would make it bigger. Here, we
> + // count each basic block as a single unit.
> + //
> + InlineCost += Caller->size()/20;
>
> It discourages inlining into very big functions. (100 basic blocks in the caller = 1 instruction in the callee.) Does anybody remember the rationale behind that heuristic?
>
> I am currently looking at a very big function with enough basic blocks that the heuristic effectively disables inlining at -Os. Even for trivial functions that would shrink the size of the function!
No, it seems reasonable to zap it. The only reason I can imagine for something like this is to prevent compile time explosion.
-Chris
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