[AMDGPU] Clear BreakPhiNodesCache in-between functions

[Pierre-vh]

Summary

Otherwise stale pointers pollute the cache and
when a dead PHI's memory is reused for another PHI, we can get a false positive hit in the cache.

[arsenm]

llvm/lib/Target/AMDGPU/AMDGPUCodeGenPrepare.cpp

322

Probably should do this on the exit. OldPM at least had a dedicated callbck for this

llvm/lib/Target/AMDGPU/AMDGPUCodeGenPrepare.cpp

public:
   bool runOnFunction(Function &F) override;
   bool doInitialization(Module &M) override;
   StringRef getPassName() const override { return "AMDGPU IR optimizations"; }
 };
 
 } // end anonymous namespace
 
 bool AMDGPUCodeGenPrepareImpl::run(Function &F) {
+  BreakPhiNodesCache.clear();
   bool MadeChange = false;
 
   Function::iterator NextBB;
   for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; FI = NextBB) {
     BasicBlock *BB = &*FI;
     NextBB = std::next(FI);
 
     BasicBlock::iterator Next;