[PATCH] D137642: [X86][CodeGen] Fix crash in hotpatch

[Sylvain Audi via Phabricator via llvm-commits]

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This patch fixes crashes (asserts) encountered in some cases while activating hotpatch using `-fms-hotpatch`, or `clang-cl /HOTPATCH`.

`PatchableFunction` pass emits a `TargetOpcode::PATCHABLE_OP` at the first LLVM-IR instruction that generates machine code. The search for that instruction was done with a local helper that hasn't been updated along with the addition of new LLVM-IR instructions.

Example crash: https://godbolt.org/z/8M9vGajs9
In this example, `DBG_INSTR_REF` is selected for `TargetOpcode::PATCHABLE_OP`; lowering that instruction asserts as the metadata-typed operands are unexpected.

Also, the search for the first instruction was assuming that one would be found, asserting otherwise. 
Such case may happen in the case of an empty function that is unreachable ( in C/C++, a simple example is `int f() {}` )


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D137642

Files:
  llvm/lib/CodeGen/PatchableFunction.cpp
  llvm/test/CodeGen/X86/patchable-prologue-debuginfo.ll
  llvm/test/CodeGen/X86/patchable-prologue.ll

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