CodeGen: Fix multiple runs of VirtRegMap

[arsenm]

This is showing some unexpected test changes

llvm/lib/CodeGen/VirtRegMap.cpp

void VirtRegRewriter::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.addPreserved<LiveIntervals>();
   AU.addRequired<SlotIndexes>();
   AU.addPreserved<SlotIndexes>();
   AU.addRequired<LiveDebugVariables>();
   AU.addRequired<LiveStacks>();
   AU.addPreserved<LiveStacks>();
   AU.addRequired<VirtRegMap>();
 
-  if (!ClearVirtRegs)
+  if (!ClearVirtRegs) {
     AU.addPreserved<LiveDebugVariables>();
+    AU.addPreserved<VirtRegMap>();
+  }
 
   MachineFunctionPass::getAnalysisUsage(AU);
 }
 
 bool VirtRegRewriter::runOnMachineFunction(MachineFunction &fn) {
   MF = &fn;
   TRI = MF->getSubtarget().getRegisterInfo();
   TII = MF->getSubtarget().getInstrInfo();

llvm/test/CodeGen/AMDGPU/llc-pipeline.ll

 ; GCN-O1-NEXT:         Live Register Matrix
 ; GCN-O1-NEXT:         Bundle Machine CFG Edges
 ; GCN-O1-NEXT:         Spill Code Placement Analysis
 ; GCN-O1-NEXT:         Lazy Machine Block Frequency Analysis
 ; GCN-O1-NEXT:         Machine Optimization Remark Emitter
 ; GCN-O1-NEXT:         Greedy Register Allocator
 ; GCN-O1-NEXT:         Virtual Register Rewriter
 ; GCN-O1-NEXT:         SI lower SGPR spill instructions
-; GCN-O1-NEXT:         Virtual Register Map
 ; GCN-O1-NEXT:         Live Register Matrix
 ; GCN-O1-NEXT:         Machine Optimization Remark Emitter
 ; GCN-O1-NEXT:         Greedy Register Allocator
 ; GCN-O1-NEXT:         GCN NSA Reassign
 ; GCN-O1-NEXT:         Virtual Register Rewriter
 ; GCN-O1-NEXT:         Stack Slot Coloring
 ; GCN-O1-NEXT:         Machine Copy Propagation Pass
 ; GCN-O1-NEXT:         Machine Loop Invariant Code Motion

 ; GCN-O1-OPTS-NEXT:         Live Register Matrix
 ; GCN-O1-OPTS-NEXT:         Bundle Machine CFG Edges
 ; GCN-O1-OPTS-NEXT:         Spill Code Placement Analysis
 ; GCN-O1-OPTS-NEXT:         Lazy Machine Block Frequency Analysis
 ; GCN-O1-OPTS-NEXT:         Machine Optimization Remark Emitter
 ; GCN-O1-OPTS-NEXT:         Greedy Register Allocator
 ; GCN-O1-OPTS-NEXT:         Virtual Register Rewriter
 ; GCN-O1-OPTS-NEXT:         SI lower SGPR spill instructions
-; GCN-O1-OPTS-NEXT:         Virtual Register Map
 ; GCN-O1-OPTS-NEXT:         Live Register Matrix
 ; GCN-O1-OPTS-NEXT:         Machine Optimization Remark Emitter
 ; GCN-O1-OPTS-NEXT:         Greedy Register Allocator
 ; GCN-O1-OPTS-NEXT:         GCN NSA Reassign
 ; GCN-O1-OPTS-NEXT:         Virtual Register Rewriter
 ; GCN-O1-OPTS-NEXT:         Stack Slot Coloring
 ; GCN-O1-OPTS-NEXT:         Machine Copy Propagation Pass
 ; GCN-O1-OPTS-NEXT:         Machine Loop Invariant Code Motion

 ; GCN-O2-NEXT:         Live Register Matrix
 ; GCN-O2-NEXT:         Bundle Machine CFG Edges
 ; GCN-O2-NEXT:         Spill Code Placement Analysis
 ; GCN-O2-NEXT:         Lazy Machine Block Frequency Analysis
 ; GCN-O2-NEXT:         Machine Optimization Remark Emitter
 ; GCN-O2-NEXT:         Greedy Register Allocator
 ; GCN-O2-NEXT:         Virtual Register Rewriter
 ; GCN-O2-NEXT:         SI lower SGPR spill instructions
-; GCN-O2-NEXT:         Virtual Register Map
 ; GCN-O2-NEXT:         Live Register Matrix
 ; GCN-O2-NEXT:         Machine Optimization Remark Emitter
 ; GCN-O2-NEXT:         Greedy Register Allocator
 ; GCN-O2-NEXT:         GCN NSA Reassign
 ; GCN-O2-NEXT:         Virtual Register Rewriter
 ; GCN-O2-NEXT:         Stack Slot Coloring
 ; GCN-O2-NEXT:         Machine Copy Propagation Pass
 ; GCN-O2-NEXT:         Machine Loop Invariant Code Motion

 ; GCN-O3-NEXT:         Live Register Matrix
 ; GCN-O3-NEXT:         Bundle Machine CFG Edges
 ; GCN-O3-NEXT:         Spill Code Placement Analysis
 ; GCN-O3-NEXT:         Lazy Machine Block Frequency Analysis
 ; GCN-O3-NEXT:         Machine Optimization Remark Emitter
 ; GCN-O3-NEXT:         Greedy Register Allocator
 ; GCN-O3-NEXT:         Virtual Register Rewriter
 ; GCN-O3-NEXT:         SI lower SGPR spill instructions
-; GCN-O3-NEXT:         Virtual Register Map
 ; GCN-O3-NEXT:         Live Register Matrix
 ; GCN-O3-NEXT:         Machine Optimization Remark Emitter
 ; GCN-O3-NEXT:         Greedy Register Allocator
 ; GCN-O3-NEXT:         GCN NSA Reassign
 ; GCN-O3-NEXT:         Virtual Register Rewriter
 ; GCN-O3-NEXT:         Stack Slot Coloring
 ; GCN-O3-NEXT:         Machine Copy Propagation Pass
 ; GCN-O3-NEXT:         Machine Loop Invariant Code Motion