Reid Barton was just noticing some  alignment perf issues  and talking about it on #ghc / #haskell-llvm

probably worth documenting it in a ticket! 

On Thu, Sep 12, 2013 at 3:28 PM, Nicolas Frisby <nicolas.frisby@gmail.com> wrote:

On my laptop, a program showed a consistent slowdown with -fdicts-strict

I didn't find any obvious causes in the Core differences, so I turned to Intel's Performance Counter Monitor for measurements. After trying a few counters, I eventuall saw that there are about an order of magnitude more misaligned memory loads with -fdicts-strict than without, so I think that may be a significant part of the slowdown. I'm not sure if these are code or data reads.

Can anyone suggest how to validate this hypothesis about misaligned reads?

A subsequent commit has changed the behavior I was seeing, so I'm not interested in alternatives means to determine if -fdicts-strict is somehow at fault — I'm just asking specifically about data/code memory alignment in GHC and how to diagnose/experiment with it.

Thanks.

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