Started 7 days 1 hr ago
Took 1 hr 19 min on green-dragon-17

Success Build rL:371485 - C:371484 - #525 (Sep 9, 2019 8:31:29 PM)

  • : 371485
  • : 371484
  • : 371453
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  1. gn build: Merge r371484 (detail/ViewSVN)
    by nico
  2. clang-misexpect: Profile Guided Validation of Performance Annotations in LLVM

    This patch contains the basic functionality for reporting potentially
    incorrect usage of __builtin_expect() by comparing the developer's
    annotation against a collected PGO profile. A more detailed proposal and
    discussion appears on the CFE-dev mailing list
    ( and a
    prototype of the initial frontend changes appear here in D65300

    We revised the work in D65300 by moving the misexpect check into the
    LLVM backend, and adding support for IR and sampling based profiles, in
    addition to frontend instrumentation.

    We add new misexpect metadata tags to those instructions directly
    influenced by the llvm.expect intrinsic (branch, switch, and select)
    when lowering the intrinsics. The misexpect metadata contains
    information about the expected target of the intrinsic so that we can
    check against the correct PGO counter when emitting diagnostics, and the
    compiler's values for the LikelyBranchWeight and UnlikelyBranchWeight.
    We use these branch weight values to determine when to emit the
    diagnostic to the user.

    A future patch should address the comment at the top of
    LowerExpectIntrisic.cpp to hoist the LikelyBranchWeight and
    UnlikelyBranchWeight values into a shared space that can be accessed
    outside of the LowerExpectIntrinsic pass. Once that is done, the
    misexpect metadata can be updated to be smaller.

    In the long term, it is possible to reconstruct portions of the
    misexpect metadata from the existing profile data. However, we have
    avoided this to keep the code simple, and because some kind of metadata
    tag will be required to identify which branch/switch/select instructions
    are influenced by the use of llvm.expect

    Patch By: paulkirth
    Differential Revision: (detail/ViewSVN)
    by phosek

Started by an SCM change (2 times)

This run spent:

  • 19 min waiting;
  • 1 hr 19 min build duration;
  • 1 hr 39 min total from scheduled to completion.
LLVM/Clang Warnings: 1 warning.
    Test Result (no failures)