[llvm] AMDGPU: Use LiveIntervals in SIOptimizeVGPRLiveRange when available (PR #222385)

[Carl Ritson via llvm-commits]

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@@ -713,7 +709,6 @@ SIOptimizeVGPRLiveRangePass::run(MachineFunction &MF,
 
   auto PA = getMachineFunctionPassPreservedAnalyses();
   PA.preserve<LiveIntervalsAnalysis>();
-  PA.preserve<LiveVariablesAnalysis>();
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perlfu wrote:

This could be conditional? `if (!LIS) ...`

https://github.com/llvm/llvm-project/pull/222385