vendor/llvm/llvm-trunk-r366426

1 files changed, 163 insertions, 0 deletions

diff --git a/lib/Target/BPF/BPFMISimplifyPatchable.cpp b/lib/Target/BPF/BPFMISimplifyPatchable.cpp
new file mode 100644
index 000000000000..e9114d7187e3
--- /dev/null
+++ b/lib/Target/BPF/BPFMISimplifyPatchable.cpp
@@ -0,0 +1,163 @@
+//===----- BPFMISimplifyPatchable.cpp - MI Simplify Patchable Insts -------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass targets a subset of instructions like below
+//    ld_imm64 r1, @global
+//    ldd r2, r1, 0
+//    add r3, struct_base_reg, r2
+//
+// Here @global should either present a AMA (abstruct member access) or
+// a patchable extern variable. And these two kinds of accesses
+// are subject to bpf load time patching. After this pass, the
+// code becomes
+//    ld_imm64 r1, @global
+//    add r3, struct_base_reg, r1
+//
+// Eventually, at BTF output stage, a relocation record will be generated
+// for ld_imm64 which should be replaced later by bpf loader:
+//    r1 = <calculated offset> or <to_be_patched_extern_val>
+//    add r3, struct_base_reg, r1
+// or
+//    ld_imm64 r1, <to_be_patched_extern_val>
+//    add r3, struct_base_reg, r1
+//
+//===----------------------------------------------------------------------===//
+
+#include "BPF.h"
+#include "BPFCORE.h"
+#include "BPFInstrInfo.h"
+#include "BPFTargetMachine.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "bpf-mi-simplify-patchable"
+
+namespace {
+
+struct BPFMISimplifyPatchable : public MachineFunctionPass {
+
+  static char ID;
+  const BPFInstrInfo *TII;
+  MachineFunction *MF;
+
+  BPFMISimplifyPatchable() : MachineFunctionPass(ID) {
+    initializeBPFMISimplifyPatchablePass(*PassRegistry::getPassRegistry());
+  }
+
+private:
+  // Initialize class variables.
+  void initialize(MachineFunction &MFParm);
+
+  bool removeLD(void);
+
+public:
+  // Main entry point for this pass.
+  bool runOnMachineFunction(MachineFunction &MF) override {
+    if (!skipFunction(MF.getFunction())) {
+      initialize(MF);
+    }
+    return removeLD();
+  }
+};
+
+// Initialize class variables.
+void BPFMISimplifyPatchable::initialize(MachineFunction &MFParm) {
+  MF = &MFParm;
+  TII = MF->getSubtarget<BPFSubtarget>().getInstrInfo();
+  LLVM_DEBUG(dbgs() << "*** BPF simplify patchable insts pass ***\n\n");
+}
+
+/// Remove unneeded Load instructions.
+bool BPFMISimplifyPatchable::removeLD() {
+  MachineRegisterInfo *MRI = &MF->getRegInfo();
+  MachineInstr *ToErase = nullptr;
+  bool Changed = false;
+
+  for (MachineBasicBlock &MBB : *MF) {
+    for (MachineInstr &MI : MBB) {
+      if (ToErase) {
+        ToErase->eraseFromParent();
+        ToErase = nullptr;
+      }
+
+      // Ensure the register format is LOAD <reg>, <reg>, 0
+      if (MI.getOpcode() != BPF::LDD && MI.getOpcode() != BPF::LDW &&
+          MI.getOpcode() != BPF::LDH && MI.getOpcode() != BPF::LDB &&
+          MI.getOpcode() != BPF::LDW32 && MI.getOpcode() != BPF::LDH32 &&
+          MI.getOpcode() != BPF::LDB32)
+        continue;
+
+      if (!MI.getOperand(0).isReg() || !MI.getOperand(1).isReg())
+        continue;
+
+      if (!MI.getOperand(2).isImm() || MI.getOperand(2).getImm())
+        continue;
+
+      unsigned DstReg = MI.getOperand(0).getReg();
+      unsigned SrcReg = MI.getOperand(1).getReg();
+      int64_t ImmVal = MI.getOperand(2).getImm();
+
+      MachineInstr *DefInst = MRI->getUniqueVRegDef(SrcReg);
+      if (!DefInst)
+        continue;
+
+      bool IsCandidate = false;
+      if (DefInst->getOpcode() == BPF::LD_imm64) {
+        const MachineOperand &MO = DefInst->getOperand(1);
+        if (MO.isGlobal()) {
+          const GlobalValue *GVal = MO.getGlobal();
+          auto *GVar = dyn_cast<GlobalVariable>(GVal);
+          if (GVar) {
+            // Global variables representing structure offset or
+            // patchable extern globals.
+            if (GVar->hasAttribute(BPFCoreSharedInfo::AmaAttr)) {
+              assert(ImmVal == 0);
+              IsCandidate = true;
+            } else if (!GVar->hasInitializer() && GVar->hasExternalLinkage() &&
+                       GVar->getSection() ==
+                           BPFCoreSharedInfo::PatchableExtSecName) {
+              if (ImmVal == 0)
+                IsCandidate = true;
+              else
+                errs() << "WARNING: unhandled patchable extern "
+                       << GVar->getName() << " with load offset " << ImmVal
+                       << "\n";
+            }
+          }
+        }
+      }
+
+      if (!IsCandidate)
+        continue;
+
+      auto Begin = MRI->use_begin(DstReg), End = MRI->use_end();
+      decltype(End) NextI;
+      for (auto I = Begin; I != End; I = NextI) {
+        NextI = std::next(I);
+        I->setReg(SrcReg);
+      }
+
+      ToErase = &MI;
+      Changed = true;
+    }
+  }
+
+  return Changed;
+}
+
+} // namespace
+
+INITIALIZE_PASS(BPFMISimplifyPatchable, DEBUG_TYPE,
+                "BPF PreEmit SimplifyPatchable", false, false)
+
+char BPFMISimplifyPatchable::ID = 0;
+FunctionPass *llvm::createBPFMISimplifyPatchablePass() {
+  return new BPFMISimplifyPatchable();
+}