[BPF] Remove unused globals whose were used for jump table

Author: Yonghong Song

llvm/lib/Target/BPF/BPFAsmPrinter.cpp

@@ -52,6 +52,45 @@ bool BPFAsmPrinter::doInitialization(Module &M) {
   return false;
 }
 
+const BPFTargetMachine &BPFAsmPrinter::getBTM() const {
+  return static_cast<const BPFTargetMachine &>(TM);
+}
+
+bool BPFAsmPrinter::doFinalization(Module &M) {
+  // Remove unused globals which are previously used for jump table.
+  const BPFSubtarget *Subtarget = getBTM().getSubtargetImpl();
+  if (Subtarget->hasGotox()) {
+    std::vector<GlobalVariable *> Targets;
+    for (GlobalVariable &Global : M.globals()) {
+      if (Global.getLinkage() != GlobalValue::PrivateLinkage)
+        continue;
+      if (!Global.isConstant() || !Global.hasInitializer())
+        continue;
+
+      Constant *CV = dyn_cast<Constant>(Global.getInitializer());
+      if (!CV)
+        continue;
+      ConstantArray *CA = dyn_cast<ConstantArray>(CV);
+      if (!CA)
+        continue;
+
+      for (unsigned i = 1, e = CA->getNumOperands(); i != e; ++i) {
+        if (!dyn_cast<BlockAddress>(CA->getOperand(i)))
+          continue;
+      }
+      Targets.push_back(&Global);
+    }
+
+    for (GlobalVariable *GV : Targets) {
+      GV->replaceAllUsesWith(PoisonValue::get(GV->getType()));
+      GV->dropAllReferences();
+      GV->eraseFromParent();
+    }
+  }
+
+  return AsmPrinter::doFinalization(M);
+}
+
 void BPFAsmPrinter::printOperand(const MachineInstr *MI, int OpNum,
                                  raw_ostream &O) {
   const MachineOperand &MO = MI->getOperand(OpNum);

llvm/lib/Target/BPF/BPFAsmPrinter.h

@@ -9,6 +9,7 @@
 #ifndef LLVM_LIB_TARGET_BPF_BPFASMPRINTER_H
 #define LLVM_LIB_TARGET_BPF_BPFASMPRINTER_H
 
+#include "BPFTargetMachine.h"
 #include "BTFDebug.h"
 #include "llvm/CodeGen/AsmPrinter.h"
 
@@ -18,10 +19,11 @@ class BPFAsmPrinter : public AsmPrinter {
 public:
   explicit BPFAsmPrinter(TargetMachine &TM,
                          std::unique_ptr<MCStreamer> Streamer)
-      : AsmPrinter(TM, std::move(Streamer), ID), BTF(nullptr) {}
+      : AsmPrinter(TM, std::move(Streamer), ID), BTF(nullptr), TM(TM) {}
 
   StringRef getPassName() const override { return "BPF Assembly Printer"; }
   bool doInitialization(Module &M) override;
+  bool doFinalization(Module &M) override;
   void printOperand(const MachineInstr *MI, int OpNum, raw_ostream &O);
   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                        const char *ExtraCode, raw_ostream &O) override;
@@ -36,6 +38,9 @@ class BPFAsmPrinter : public AsmPrinter {
 
 private:
   BTFDebug *BTF;
+  TargetMachine &TM;
+
+  const BPFTargetMachine &getBTM() const;
 };
 
 } // namespace llvm