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.unaligned prefix ignored on initblk and cpblk #5236

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.unaligned prefix ignored on initblk and cpblk#5236
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area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMIenhancementProduct code improvement that does NOT require public API changes/additionshelp wanted[up-for-grabs] Good issue for external contributorsoptimizationtenet-performancePerformance related issue
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Future

Description

@cmckinsey
cmckinsey
opened on Mar 4, 2016

Strictly speaking the JIT needs to make sure to generate references that are aligned with respect to the byte size specified by any unaligned prefix on initblk and cpblk. Today's implemented ignores them.

For some architectures, generating unaligned references may cause execution faults at runtime. For others, they can be less efficient than aligned references. At the moment all the targets RyuJIT supports do not require this for correctness, but might benefit on the performance side, especially for large block operations.

The MC++ compiler does generate these block operations today with unaligned prefixes to capture the original access size when vectorizing array initialization loops to block set operations (initblk).

category:correctness
theme:msil
skill-level:intermediate
cost:small

Activity

  1. msftgits
    transferred this issue fromdotnet/coreclron Jan 30, 2020
  2. msftgits
    added this to the Future milestone on Jan 30, 2020
  3. BruceForstall
    added
    JitUntriagedCLR JIT issues needing additional triage
    on Oct 28, 2020
  4. BruceForstall
    removed
    JitUntriagedCLR JIT issues needing additional triage
    on Jan 24, 2023

  5. EgorBo commented on Jun 22, 2024

    @EgorBo
    EgorBo
    on Jun 22, 2024
    Member

    It's no longer ignored:

    runtime/src/coreclr/jit/importer.cpp

    Lines 10397 to 10402 in 0262a63

    if (isVolatile)
    {
    // Wrap with memory barriers: full-barrier + call + load-barrier
    impAppendTree(gtNewMemoryBarrier(), CHECK_SPILL_ALL, impCurStmtDI);
    impAppendTree(call, CHECK_SPILL_ALL, impCurStmtDI);
    op1 = gtNewMemoryBarrier(true);

  6. EgorBo
    closed this as completedon Jun 22, 2024
  7. github-actions
    locked and limited conversation to collaborators on Jul 23, 2024
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