[llvm] [ExtendLifetimes] Implement llvm.fake.use to extend variable lifetimes (PR #86149)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,40 @@
+; RUN: llc < %s -stop-after=finalize-isel | FileCheck %s --implicit-check-not=FAKE_USE
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arsenm wrote:

test/CodeGen/MIR is for testing of the MIR printer/parser, not tests that check MIR output. This should go to test/CodeGen/X86 

https://github.com/llvm/llvm-project/pull/86149