[LLVMdev] LiveVariables/LiveInterval on huge functions

Török Edwin edwintorok at gmail.com
Mon Apr 14 23:16:28 PDT 2008

Evan Cheng wrote:
> On Apr 14, 2008, at 10:43 AM, Chris Lattner wrote:
>> On Mon, 14 Apr 2008, [ISO-8859-1] Török Edwin wrote:
>>>> Another question to ask, is why that function became so large in the
>>>> first place [X86DAGToDAGISel::SelectCode(llvm::SDOperand)]
>>>> We have inline limits, don't we?
>>> most of functions called by SelectCode get a -30000 cost reduction
>>> because they are internal.
>>> Even if Caller.size() is 40000, the penalty is only 2000, thus we  
>>> still
>>> have negative costs.
>>> Removing the /20 factor from here improves the situation a lot,  
>>> however
>>> I think there is  a reason for /20, and it can't be just removed:
>>> InlineCost += Caller->size()/20;
>> This sounds like unanticipated fallout from Evan's recent tweaks of  
>> the inliner.  Evan, thoughts?
> Previously the inliner assign each basic block cost of 20. So this  
> line is simply estimating the number of caller basic blocks. My tweak  
> simply removed the number of basic blocks from the equation so the  
> cost of a callee is simply number of instructions * 5. I don't think  
> it should / would impact this case. Edwin, can you revert 49061 and  
> 48725 to see if they have any impact?

Reverting 49061 does have an impact. I can compile the testcase withing
1.1G of memory, and memory usage was rising slowly (except for a quick
500M->1G jump).
The patch couldn't be reverted cleanly, I had to manually revert parts
of it.

Best regards,

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