https://bugs.llvm.org/show_bug.cgi?id=26859
Sanjay Patel <[email protected]> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|NEW |RESOLVED
--- Comment #14 from Sanjay Patel <[email protected]> ---
(In reply to Simon Pilgrim from comment #13)
> https://reviews.llvm.org/D53095
Committed here:
https://reviews.llvm.org/rL344361
There's a stunning amount of vector duplication + unrolling in these tests
currently:
$ clang -O2 accum.c -S -o - -mavx | grep padd | wc -l
155
...but that's not this bug.
This is the current behavior:
$ clang -Os accum.c -S -o - -mavx | grep phadd | grep mm
vphaddd %xmm0, %xmm0, %xmm0
vphaddw %xmm0, %xmm0, %xmm0
$ clang -O2 accum.c -S -o - -mavx | grep phadd | grep mm
$ clang -O2 accum.c -S -o - -mavx -march=btver2 | grep phadd | grep mm
vphaddd %xmm0, %xmm0, %xmm0
vphaddw %xmm0, %xmm0, %xmm0
Ie, if we are optimizing for size or Jaguar, we'll use horizontal ops,
otherwise, we use regular ops and shuffles.
It's possible that our combiner predicate will need adjustments to optimize
that decision depending on code pattern and uarch, but we now have that
ability. Ideally, we can refine the choice using CPU instruction
latency/throughput models rather than with the DAG heuristic in the patch, but
that's also another bug.
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