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[AArch64][SME] Disable tail-call optimization for __arm_locally_streaming functions. #65258

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merged 1 commit into from
Sep 4, 2023
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[AArch64][SME] Disable tail-call optimization for __arm_locally_streaming functions. #65258

merged 1 commit into from
Sep 4, 2023

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@sdesmalen-arm sdesmalen-arm commented Sep 4, 2023 •
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When calling a function which requires no streaming-mode change from an __arm_locally_streaming function, LLVM would otherwise emit:

// function prologue
smstart
b streaming_compatible_function // tail call
// never an smstop

@sdesmalen-arm
[AArch64][SME] Disable tail-call optimization for __arm_locally_strea…
3a45f9c 
…ming functions.

When calling e.g. a streaming-compatible function (which requires no streaming-mode change),
LLVM would otherwise emit:

  // function prologue
  smstart
  b streaming_compatible_function   // tail call
  // never an smstop
@sdesmalen-arm sdesmalen-arm requested a review from a team as a code owner September 4, 2023 12:33
MDevereau
MDevereau approved these changes Sep 4, 2023
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When calling e.g. a streaming-compatible function (which requires no streaming-mode change)

nit, commit message using e.g. implies there are other cases you know of but there's only one test case here

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When calling e.g. a streaming-compatible function (which requires no streaming-mode change)

nit, commit message using e.g. implies there are other cases you know of but there's only one test case here

The other case would be where the callee would be an __arm_streaming function, which would have caused CallerAttrs.requiresSMChange(CalleeAttrs) to return false. I didn't think it was useful to add a test-case for this, because a call for __arm_locally_streaming -> __arm_streaming_compatible results in the same answer for CallerAttrs.requiresSMChange(CalleeAttrs), and this interface is already tested extensively in another test.

@sdesmalen-arm sdesmalen-arm merged commit dbf9b93 into llvm:main Sep 4, 2023
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@sdesmalen-arm sdesmalen-arm deleted the fix-streaming-body-tail-call branch September 4, 2023 14:11
avillega pushed a commit to avillega/llvm-project that referenced this pull request Sep 11, 2023
@sdesmalen-arm @avillega
[AArch64][SME] Disable tail-call optimization for __arm_locally_strea…
aa91df0 
…ming functions. (llvm#65258)

When calling a function which requires no streaming-mode change from an
__arm_locally_streaming function, LLVM would otherwise emit:

  // function prologue
  smstart
  b streaming_compatible_function   // tail call
  // never an smstop
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@MDevereau MDevereau MDevereau approved these changes

@paulwalker-arm paulwalker-arm Awaiting requested review from paulwalker-arm

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