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Permit vectorization of non-recursive atomic operations #7346

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abadams merged 2 commits into from
Feb 15, 2023
Merged

Permit vectorization of non-recursive atomic operations #7346

abadams merged 2 commits into from
Feb 15, 2023

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@abadams
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@abadams abadams commented Feb 13, 2023

Pre-vectorization, the code in the included test lowers to:

      let t16 = f0[((f1.s3.r6$x.r6$x*16) + f1.s3.r6$x.r7) + 2] + f0[((f1.s3.r6$x.r6$x*16) + f1.s3.r6$x.r7) + 1]
      let t17 = (((f1.s3.r6$x.r6$x*16) + f1.s3.r6$x.r7) - f1.0.min.0) + 2
      atomic {
        f1.0[t17] = t16
      }
      let t18 = ((f1.s3.r6$x.r6$x*16) + f1.s3.r6$x.r7) - f1.0.min.0
      let t19 = f0[((f1.s3.r6$x.r6$x*16) + f1.s3.r6$x.r7) + 2] + f0[((f1.s3.r6$x.r6$x*16) + f1.s3.r6$x.r7) + 1]
      let t20 = (((f1.s3.r6$x.r6$x*16) + f1.s3.r6$x.r7) - f1.0.min.0) + 2
      atomic {
        f1.1[t20] = f1.0[t18] + t19
      }

which then scalarizes, even though those atomic nodes could be vectorized just fine, because each atomic operation is non-recursive. This PR enables vectorization of such atomic nodes.

Note that the code in the test uses an unsafe override of the associativity/commutativity check, and while it's safe to vectorize as written, if you change it a little bit, e.g. by flipping the order of the tuple components, it's not.

@steven-johnson
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steven-johnson commented Feb 13, 2023

which then scalarizes

Related: IMHO we should consider emitting warnings when code scalarizes; at this point it should be pretty uncommon to happen, but when it does it's a gigantic time sink and the cause won't be obvious to the casual coder.

@abadams abadams requested a review from alexreinking February 14, 2023 17:25
@abadams abadams merged commit 18eb7d8 into main Feb 15, 2023
ardier pushed a commit to ardier/Halide-mutation that referenced this pull request Mar 3, 2024
@abadams @ardier
Permit vectorization of non-recursive atomic operations (halide#7346)
e703f0d 
* Vectorization of non-recursive atomic operations

* Remove dead Vars
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