[llvm-dev] About CodeGen quality

[陳韋任 via llvm-dev]

>
> I guess my previous reply was a bit too terse.
>
> We don't want to narrow loads early in the optimization pipeline because
> it tends to hide relationships between bitfields.  In particular,
> overlapping loads/stores are more difficult to optimize.  We want
> EarlyCSE/GVN/DSE/etc. to see the full-width loads and stores to make them
> more effective.
>
> Currently, we do narrowing in DAGCombine.  D30416 is a proposal to move
> that slightly earlier, to the late stages of the IR optimization pipeline,
> so we can avoid the limitations of SelectionDAG.
>
> If you read the whole discussion on that patch, it goes into more detail
> about this.
>

​Thanks. I was only reading the summary of the patch. :-)

Regards,
chenwj​

-- 
Wei-Ren Chen (陳韋任)
Homepage: https://people.cs.nctu.edu.tw/~chenwj
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