1 files changed, 98 insertions, 0 deletions
diff --git a/contrib/llvm-project/llvm/lib/CodeGen/PatchableFunction.cpp b/contrib/llvm-project/llvm/lib/CodeGen/PatchableFunction.cpp
new file mode 100644
index 000000000000..9449f143366f
--- /dev/null
+++ b/contrib/llvm-project/llvm/lib/CodeGen/PatchableFunction.cpp
@@ -0,0 +1,98 @@
+//===-- PatchableFunction.cpp - Patchable prologues for LLVM -------------===//
+//
+// 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 file implements edits function bodies in place to support the
+// "patchable-function" attribute.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/TargetInstrInfo.h"
+#include "llvm/CodeGen/TargetSubtargetInfo.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+#include "llvm/PassRegistry.h"
+
+using namespace llvm;
+
+namespace {
+struct PatchableFunction : public MachineFunctionPass {
+  static char ID; // Pass identification, replacement for typeid
+  PatchableFunction() : MachineFunctionPass(ID) {
+    initializePatchableFunctionPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnMachineFunction(MachineFunction &F) override;
+   MachineFunctionProperties getRequiredProperties() const override {
+    return MachineFunctionProperties().set(
+        MachineFunctionProperties::Property::NoVRegs);
+  }
+};
+}
+
+bool PatchableFunction::runOnMachineFunction(MachineFunction &MF) {
+  if (MF.getFunction().hasFnAttribute("patchable-function-entry")) {
+    MachineBasicBlock &FirstMBB = *MF.begin();
+    const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
+    // The initial .loc covers PATCHABLE_FUNCTION_ENTER.
+    BuildMI(FirstMBB, FirstMBB.begin(), DebugLoc(),
+            TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER));
+    return true;
+  }
+
+  if (!MF.getFunction().hasFnAttribute("patchable-function"))
+    return false;
+
+#ifndef NDEBUG
+  Attribute PatchAttr = MF.getFunction().getFnAttribute("patchable-function");
+  StringRef PatchType = PatchAttr.getValueAsString();
+  assert(PatchType == "prologue-short-redirect" && "Only possibility today!");
+#endif
+
+  auto &FirstMBB = *MF.begin();
+  auto *TII = MF.getSubtarget().getInstrInfo();
+
+  MachineBasicBlock::iterator FirstActualI = llvm::find_if(
+      FirstMBB, [](const MachineInstr &MI) { return !MI.isMetaInstruction(); });
+
+  if (FirstActualI == FirstMBB.end()) {
+    // As of Microsoft documentation on /hotpatch feature, we must ensure that
+    // "the first instruction of each function is at least two bytes, and no
+    // jump within the function goes to the first instruction"
+
+    // When the first MBB is empty, insert a patchable no-op. This ensures the
+    // first instruction is patchable in two special cases:
+    // - the function is empty (e.g. unreachable)
+    // - the function jumps back to the first instruction, which is in a
+    // successor MBB.
+    BuildMI(&FirstMBB, DebugLoc(), TII->get(TargetOpcode::PATCHABLE_OP))
+        .addImm(2)
+        .addImm(TargetOpcode::PATCHABLE_OP);
+    MF.ensureAlignment(Align(16));
+    return true;
+  }
+
+  auto MIB = BuildMI(FirstMBB, FirstActualI, FirstActualI->getDebugLoc(),
+                     TII->get(TargetOpcode::PATCHABLE_OP))
+                 .addImm(2)
+                 .addImm(FirstActualI->getOpcode());
+
+  for (auto &MO : FirstActualI->operands())
+    MIB.add(MO);
+
+  FirstActualI->eraseFromParent();
+  MF.ensureAlignment(Align(16));
+  return true;
+}
+
+char PatchableFunction::ID = 0;
+char &llvm::PatchableFunctionID = PatchableFunction::ID;
+INITIALIZE_PASS(PatchableFunction, "patchable-function",
+                "Implement the 'patchable-function' attribute", false, false)