[PATCH] D98038: [AMDGPU] Fix the dead frame indices during custom spill lowering.

[Scott Linder via Phabricator via llvm-commits]

scott.linder accepted this revision.
scott.linder added a comment.
This revision is now accepted and ready to land.

In D98038#2611266 <https://reviews.llvm.org/D98038#2611266>, @arsenm wrote:

> I'm not sure if replacing with noreg or just erasing the dbg_value is better

The correct thing is to replace the operand with `$noreg`, not delete the `DBG_VALUE`. If we delete the `DBG_VALUE` entirely we may be incorrectly extending the range of an earlier `DBG_VALUE`. For example:

  DBG_VALUE $rax, !"var"
  ...
  SPILL %stack.0 <- $rax
  DBG_VALUE %stack.0, !"var" ; implicitly "kills" previous DBG_VALUE, "var" now exclusively located in %stack.0
  ...
  CLOBBER $rax
  ...

If we eliminate the second `DBG_VALUE` we may end up with something like:

  DBG_VALUE $rax, !"var"
  ...
  ; no implicit "kill"
  CLOBBER $rax
  ... ; now incorrectly describes the location of "var" as $rax even after the clobber

If we just replace the operand, we continue to kill any existing `DBG_VALUE`.


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https://reviews.llvm.org/D98038