LiveIntervalAnalysis: Remove LiveVariables requirement

This requirement was a huge hack to keep LiveVariables alive because it
was optionally used by TwoAddressInstructionPass and PHIElimination.
However we have AnalysisUsage::addUsedIfAvailable() which we can use in
those passes.

This re-applies r260806 with LiveVariables manually added to PowerPC to
hopefully not break the stage 2 bots this time.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267954 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/LiveIntervalAnalysis.cpp

@@ -9,8 +9,7 @@
 //
 // This file implements the LiveInterval analysis pass which is used
 // by the Linear Scan Register allocator. This pass linearizes the
-// basic blocks of the function in DFS order and uses the
+// basic blocks of the function in DFS order and computes live intervals for
-// LiveVariables pass to conservatively compute live intervals for
 // each virtual and physical register.
 //
 //===----------------------------------------------------------------------===//
@@ -46,7 +45,6 @@ char &llvm::LiveIntervalsID = LiveIntervals::ID;
 INITIALIZE_PASS_BEGIN(LiveIntervals, "liveintervals",
                 "Live Interval Analysis", false, false)
 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LiveVariables)
 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
 INITIALIZE_PASS_END(LiveIntervals, "liveintervals",
@@ -75,10 +73,6 @@ void LiveIntervals::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.setPreservesCFG();
   AU.addRequired<AAResultsWrapperPass>();
   AU.addPreserved<AAResultsWrapperPass>();
-  // LiveVariables isn't really required by this analysis, it is only required
-  // here to make sure it is live during TwoAddressInstructionPass and
-  // PHIElimination. This is temporary.
-  AU.addRequired<LiveVariables>();
   AU.addPreserved<LiveVariables>();
   AU.addPreservedID(MachineLoopInfoID);
   AU.addRequiredTransitiveID(MachineDominatorsID);

lib/CodeGen/PHIElimination.cpp

@@ -120,6 +120,7 @@ INITIALIZE_PASS_END(PHIElimination, "phi-node-elimination",
                     "Eliminate PHI nodes for register allocation", false, false)
 
 void PHIElimination::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.addUsedIfAvailable<LiveVariables>();
   AU.addPreserved<LiveVariables>();
   AU.addPreserved<SlotIndexes>();
   AU.addPreserved<LiveIntervals>();

lib/CodeGen/TwoAddressInstructionPass.cpp

@@ -156,6 +156,7 @@ public:
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.setPreservesCFG();
     AU.addRequired<AAResultsWrapperPass>();
+    AU.addUsedIfAvailable<LiveVariables>();
     AU.addPreserved<LiveVariables>();
     AU.addPreserved<SlotIndexes>();
     AU.addPreserved<LiveIntervals>();

lib/Target/PowerPC/PPCTargetMachine.cpp

@@ -15,6 +15,7 @@
 #include "PPC.h"
 #include "PPCTargetObjectFile.h"
 #include "PPCTargetTransformInfo.h"
+#include "llvm/CodeGen/LiveVariables.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/LegacyPassManager.h"
@@ -387,8 +388,14 @@ void PPCPassConfig::addPreRegAlloc() {
     insertPass(VSXFMAMutateEarly ? &RegisterCoalescerID : &MachineSchedulerID,
                &PPCVSXFMAMutateID);
   }
-  if (getPPCTargetMachine().getRelocationModel() == Reloc::PIC_)
+  if (getPPCTargetMachine().getRelocationModel() == Reloc::PIC_) {
+    // FIXME: LiveVariables should not be necessary here!
+    // PPCTLSDYnamicCallPass uses LiveIntervals which previously dependet on
+    // LiveVariables. This (unnecessary) dependency has been removed now,
+    // however a stage-2 clang build fails without LiveVariables computed here.
+    addPass(&LiveVariablesID, false);
     addPass(createPPCTLSDynamicCallPass());
+  }
   if (EnableExtraTOCRegDeps)
     addPass(createPPCTOCRegDepsPass());
 }