[llvm] [BPF] Report Undefined Behavior from IR (PR #126858)

[via llvm-commits]

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@@ -0,0 +1,118 @@
+//===---------------- BPFAdjustOpt.cpp - Adjust Optimization --------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Check 'undef' and 'unreachable' IRs and issue proper warnings.
+//
+//===----------------------------------------------------------------------===//
+
+#include "BPF.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Type.h"
+#include "llvm/IR/Value.h"
+#include "llvm/Pass.h"
+
+#define DEBUG_TYPE "bpf-check-undef-ir"
+
+using namespace llvm;
+
+namespace {
+
+class BPFCheckUndefIR final : public ModulePass {
+  bool runOnModule(Module &F) override;
+
+public:
+  static char ID;
+  BPFCheckUndefIR() : ModulePass(ID) {}
+
+private:
+  void BPFCheckUndefIRImpl(Function &F);
+  void BPFCheckInst(Function &F, BasicBlock &BB, Instruction &I);
+  void HandleReturnInsn(Function &F, ReturnInst *I);
+  void HandleUnreachableInsn(Function &F, BasicBlock &BB, Instruction &I);
+};
+} // End anonymous namespace
+
+char BPFCheckUndefIR::ID = 0;
+INITIALIZE_PASS(BPFCheckUndefIR, DEBUG_TYPE, "BPF Check Undef IRs", false,
+                false)
+
+ModulePass *llvm::createBPFCheckUndefIR() { return new BPFCheckUndefIR(); }
+
+void BPFCheckUndefIR::HandleReturnInsn(Function &F, ReturnInst *I) {
+  Value *RetValue = I->getReturnValue();
+  // PoisonValue is a special UndefValue where compiler intentionally to
+  // poisons a value since it shouldn't be used.
+  if (!RetValue || isa<PoisonValue>(RetValue) || !isa<UndefValue>(RetValue))
----------------
4ast wrote:

Looks like undef is deprecated.
Do we have to check it or PoisonValue is enough?

https://github.com/llvm/llvm-project/pull/126858