llvm/lib/Target/BPF/BPFCheckAndAdjustIR.cpp

   1 //===------------ BPFCheckAndAdjustIR.cpp - Check and Adjust IR -----------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // Check IR and adjust IR for verifier friendly codes.
  10 // The following are done for IR checking:
  11 //   - no relocation globals in PHI node.
  12 // The following are done for IR adjustment:
  13 //   - remove __builtin_bpf_passthrough builtins. Target independent IR
  14 //     optimizations are done and those builtins can be removed.
  15 //
  16 //===----------------------------------------------------------------------===//
  17
  18 #include "BPF.h"
  19 #include "BPFCORE.h"
  20 #include "BPFTargetMachine.h"
  21 #include "llvm/IR/DebugInfoMetadata.h"
  22 #include "llvm/IR/GlobalVariable.h"
  23 #include "llvm/IR/Instruction.h"
  24 #include "llvm/IR/Instructions.h"
  25 #include "llvm/IR/Module.h"
  26 #include "llvm/IR/Type.h"
  27 #include "llvm/IR/User.h"
  28 #include "llvm/IR/Value.h"
  29 #include "llvm/Pass.h"
  30 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  31
  32 #define DEBUG_TYPE "bpf-check-and-opt-ir"
  33
  34 using namespace llvm;
  35
  36 namespace {
  37
  38 class BPFCheckAndAdjustIR final : public ModulePass {
  39   bool runOnModule(Module &F) override;
  40
  41 public:
  42   static char ID;
  43   BPFCheckAndAdjustIR() : ModulePass(ID) {}
  44
  45 private:
  46   void checkIR(Module &M);
  47   bool adjustIR(Module &M);
  48   bool removePassThroughBuiltin(Module &M);
  49 };
  50 } // End anonymous namespace
  51
  52 char BPFCheckAndAdjustIR::ID = 0;
  53 INITIALIZE_PASS(BPFCheckAndAdjustIR, DEBUG_TYPE, "BPF Check And Adjust IR",
  54                 false, false)
  55
  56 ModulePass *llvm::createBPFCheckAndAdjustIR() {
  57   return new BPFCheckAndAdjustIR();
  58 }
  59
  60 void BPFCheckAndAdjustIR::checkIR(Module &M) {
  61   // Ensure relocation global won't appear in PHI node
  62   // This may happen if the compiler generated the following code:
  63   //   B1:
  64   //      g1 = @llvm.skb_buff:0:1...
  65   //      ...
  66   //      goto B_COMMON
  67   //   B2:
  68   //      g2 = @llvm.skb_buff:0:2...
  69   //      ...
  70   //      goto B_COMMON
  71   //   B_COMMON:
  72   //      g = PHI(g1, g2)
  73   //      x = load g
  74   //      ...
  75   // If anything likes the above "g = PHI(g1, g2)", issue a fatal error.
  76   for (Function &F : M)
  77     for (auto &BB : F)
  78       for (auto &I : BB) {
  79         PHINode *PN = dyn_cast<PHINode>(&I);
  80         if (!PN || PN->use_empty())
  81           continue;
  82         for (int i = 0, e = PN->getNumIncomingValues(); i < e; ++i) {
  83           auto *GV = dyn_cast<GlobalVariable>(PN->getIncomingValue(i));
  84           if (!GV)
  85             continue;
  86           if (GV->hasAttribute(BPFCoreSharedInfo::AmaAttr) ||
  87               GV->hasAttribute(BPFCoreSharedInfo::TypeIdAttr))
  88             report_fatal_error("relocation global in PHI node");
  89         }
  90       }
  91 }
  92
  93 bool BPFCheckAndAdjustIR::removePassThroughBuiltin(Module &M) {
  94   // Remove __builtin_bpf_passthrough()'s which are used to prevent
  95   // certain IR optimizations. Now major IR optimizations are done,
  96   // remove them.
  97   bool Changed = false;
  98   CallInst *ToBeDeleted = nullptr;
  99   for (Function &F : M)
 100     for (auto &BB : F)
 101       for (auto &I : BB) {
 102         if (ToBeDeleted) {
 103           ToBeDeleted->eraseFromParent();
 104           ToBeDeleted = nullptr;
 105         }
 106
 107         auto *Call = dyn_cast<CallInst>(&I);
 108         if (!Call)
 109           continue;
 110         auto *GV = dyn_cast<GlobalValue>(Call->getCalledOperand());
 111         if (!GV)
 112           continue;
 113         if (!GV->getName().startswith("llvm.bpf.passthrough"))
 114           continue;
 115         Changed = true;
 116         Value *Arg = Call->getArgOperand(1);
 117         Call->replaceAllUsesWith(Arg);
 118         ToBeDeleted = Call;
 119       }
 120   return Changed;
 121 }
 122
 123 bool BPFCheckAndAdjustIR::adjustIR(Module &M) {
 124   return removePassThroughBuiltin(M);
 125 }
 126
 127 bool BPFCheckAndAdjustIR::runOnModule(Module &M) {
 128   checkIR(M);
 129   return adjustIR(M);
 130 }