[PATCH] D27913: [XRay] Fix assertion failure on empty machine basic blocks (PR 31424)

[Dean Michael Berris via Phabricator via llvm-commits]

dberris created this revision.
dberris added a reviewer: chandlerc.
dberris added subscribers: llvm-commits, varno.

The original version of the code in XRayInstrumentation.cpp assumed that
functions may not have empty machine basic blocks (or that the first one
couldn't be). This change addresses that by special-casing that specific
situation.

We provide a .mir test-case to make sure we're handling this
appropriately.

Fixes llvm.org/PR31424.


https://reviews.llvm.org/D27913

Files:
  lib/CodeGen/XRayInstrumentation.cpp
  test/CodeGen/X86/xray-empty-firstmbb.mir

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