[llvm-dev] Aggregate load/stores

Philip Reames via llvm-dev llvm-dev at lists.llvm.org
Mon Aug 17 10:09:05 PDT 2015

On 08/17/2015 12:13 AM, deadal nix via llvm-dev wrote:
> 2015-08-16 23:21 GMT-07:00 David Majnemer <david.majnemer at gmail.com 
> <mailto:david.majnemer at gmail.com>>:
>     Because a solution which doesn't generalize is not a very powerful
>     solution.  What happens when somebody says that they want to use
>     atomics + large aggregate loads and stores? Give them yet another,
>     different answer? That would mean our earlier, less general
>     answer, approach was either a bandaid (bad) or the new answer
>     requires a parallel code path in their frontend (worse).
> It is expected from atomics/volatile to work differently. That is the 
> whole point of them.
> A lot of optimization in InstCombine plain ignore atomic/volatile 
> load/store. That is expected.
I agree with this particular point.  If we limited the optimizer to 
treating all load and stores the same, we'd have a much weaker 
optimizer.  Treating atomic vs non-atomic FCAs differently from an 
optimization standpoint seems potentially reasonable.  I would not want 
to treat them differently from a correctness/lowering strategy 
standpoint.  (i.e. both the input and output from instcombine need to 
trigger somewhat sane results from the backend.)

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