[Agda] more on type check performance

[Sergei Meshveliani]

I wrote today about GHC that with GHC I always manage to sensibly
optimize my Haskell programs for performance.
But I need to add the following.
Sometimes, in rare cases, I cannot find the cost consuming place other
than by using the GHC profiling, with manually setting cost centers in
the source. This always helps me to discover the place (and this place
never occurs the one that I expected). 

Regards,

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Sergei