In that context large longs means HUNDREDS or THOUSANDS of bits, not 64 :) Can you show us a full runnable example that illustrates this?


On Wed, Feb 27, 2013 at 12:10 PM, Roger Flores <> wrote:
Hi guys.  I've been looking at two simple routines using jitviewer to figure out why they're so much slower than expected.

I've also noticed that has the line "Bad examples include doing computations with
large longs – which is performed by unoptimizable support code.".  I'm worried that my 32 bit int code is falling into this, and I'm wondering what I can do to avoid it?

Trivial code like

if (self.low ^ self.high) & 0x80000000 == 0:

is expanding into several dozen asm instructions.  I'm suspecting that lines like 

self.low = (self.low << 1) & 0xffffffff

with it's shift left are convincing the jit to consider the int to need 64 bits (large long?) instead of 32.

Ideas?  The asm is clearly operating on QWORDs and calling routines to do the bit arithmetic instead of single instructions.  Is this what that line in performance.html is warning about?


BTW Fijal's jitviewer is a *must see* for anyone interested in how pypy makes their code fast!

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