[llvm] [CodeGen] Mark LIFETIME_START and LIFETIME_END as not safe to move (PR #211179)

[Luke Lau via llvm-commits]

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@@ -1403,11 +1403,6 @@ bool MachineInstr::wouldBeTriviallyDead() const {
   if (isFakeUse())
     return false;
 
-  // LIFETIME markers should be preserved.
-  // FIXME: Why are LIFETIME markers not considered in MachineInstr::isPosition?
-  if (isLifetimeMarker())
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lukel97 wrote:

The FIXME was discussed a bit on discord and I'm not 100% sure what isPosition really entails. The commit that adds isPosition doesn't really describe it much: https://github.com/llvm/llvm-project/commit/b1f25f1b93fd9

Added the FIXME back anyway

https://github.com/llvm/llvm-project/pull/211179