HdMergingSceneIndex: improve performance of _RebuildInputsPathTable()

[cameronwhite]

Description of Change(s)

This became an n^2 loop when there were many inputs with non-overlapping scene roots (e.g. native instancing with a large number of prototypes) and the size of _inputsPathTable approached the number of inputs.

In this scenario the majority of the scene roots are of the form:

• /UsdNiPropagatedPrototypes/__hash_1__/__Prototype_1/UsdNiInstancer
• ...
• /UsdNiPropagatedPrototypes/__hash_N__/__Prototype_1/UsdNiInstancer

We can instead use FindSubtreeRange(sceneRoot) to find which table entries each input should be added to, eliminating the HasPrefix() check against every entry.

Attached is an example scene with 10k prototypes (usdskel_instanced.zip) along before & after stats of time spent in _RebuildInputsPathTable()

Before:

    0.002 ms     0.002 ms       1 samples    |   | pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable
    0.001 ms     0.001 ms       3 samples    |   |   | pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable
    0.002 ms     0.002 ms       2 samples    |   |   |   pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable
    0.001 ms     0.001 ms       2 samples    |   |   pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable
    6.611 ms     6.611 ms   20000 samples    |   |   |   |   |   |   |   pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable
 1958.234 ms  1958.234 ms       1 samples    |   |   |   |   |   |   | pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable
    0.003 ms     0.003 ms       1 samples    |   |   |   |   pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable
    0.003 ms     0.003 ms       1 samples    |   |   pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable

After:

    0.002 ms     0.002 ms       1 samples    |   | pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable
    0.001 ms     0.001 ms       3 samples    |   |   | pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable
    0.002 ms     0.002 ms       2 samples    |   |   |   pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable
    0.001 ms     0.001 ms       2 samples    |   |   pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable
    5.930 ms     5.930 ms   20000 samples    |   |   |   |   |   |   |   pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable
    5.691 ms     5.691 ms       1 samples    |   |   |   |   |   |   | pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable
    0.004 ms     0.004 ms       1 samples    |   |   |   |   pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable
    0.002 ms     0.002 ms       1 samples    |   |   pxrInternal_v0_25_8__pxrReserved__::HdMergingSceneIndex::_RebuildInputsPathTable

Link to proposal (if applicable)

Fixes Issue(s)

N/A

Checklist

• I have created this PR based on the dev branch

• I have followed the coding conventions

• I have added unit tests that exercise this functionality (Reference:
  testing guidelines)

• I have verified that all unit tests pass with the proposed changes

• I have submitted a signed Contributor License Agreement (Reference:
  Contributor License Agreement instructions)

[jesschimein]

Filed as internal issue #USD-11281

(This is an automated message. See here for more information.)

[cameronwhite]

This can be closed since 9f005c1 made the same change