4 files changed, 117 insertions, 5 deletions
diff --git a/llvm/lib/Transforms/Scalar/CMakeLists.txt b/llvm/lib/Transforms/Scalar/CMakeLists.txt
index 2684cee838f..f62cf6b92fe 100644
--- a/llvm/lib/Transforms/Scalar/CMakeLists.txt
+++ b/llvm/lib/Transforms/Scalar/CMakeLists.txt
@@ -32,6 +32,7 @@ add_llvm_library(LLVMScalarOpts
   LoopVersioningLICM.cpp
   LowerAtomic.cpp
   LowerExpectIntrinsic.cpp
+  LowerGuardIntrinsic.cpp
   MemCpyOptimizer.cpp
   MergedLoadStoreMotion.cpp
   NaryReassociate.cpp
diff --git a/llvm/lib/Transforms/Scalar/LowerGuardIntrinsic.cpp b/llvm/lib/Transforms/Scalar/LowerGuardIntrinsic.cpp
new file mode 100644
index 00000000000..5f5dd197b44
--- /dev/null
+++ b/llvm/lib/Transforms/Scalar/LowerGuardIntrinsic.cpp
@@ -0,0 +1,108 @@
+//===- LowerGuardIntrinsic.cpp - Lower the guard intrinsic ---------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass lowers the llvm.experimental.guard intrinsic to a conditional call
+// to @llvm.experimental.deoptimize.  Once this happens, the guard can no longer
+// be widened.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+
+using namespace llvm;
+
+namespace {
+struct LowerGuardIntrinsic : public FunctionPass {
+  static char ID;
+  LowerGuardIntrinsic() : FunctionPass(ID) {
+    initializeLowerGuardIntrinsicPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnFunction(Function &F) override;
+};
+}
+
+static void MakeGuardControlFlowExplicit(Function *DeoptIntrinsic,
+                                         CallInst *CI) {
+  OperandBundleDef DeoptOB(*CI->getOperandBundle(LLVMContext::OB_deopt));
+  SmallVector<Value *, 4> Args(std::next(CI->arg_begin()), CI->arg_end());
+
+  auto *CheckBB = CI->getParent();
+  auto *DeoptBlockTerm =
+      SplitBlockAndInsertIfThen(CI->getArgOperand(0), CI, true);
+
+  auto *CheckBI = cast<BranchInst>(CheckBB->getTerminator());
+
+  // SplitBlockAndInsertIfThen inserts control flow that branches to
+  // DeoptBlockTerm if the condition is true.  We want the opposite.
+  CheckBI->swapSuccessors();
+
+  CheckBI->getSuccessor(0)->setName("guarded");
+  CheckBI->getSuccessor(1)->setName("deopt");
+
+  IRBuilder<> B(DeoptBlockTerm);
+  auto *DeoptCall = B.CreateCall(DeoptIntrinsic, Args, {DeoptOB}, "");
+
+  if (DeoptIntrinsic->getReturnType()->isVoidTy()) {
+    B.CreateRetVoid();
+  } else {
+    DeoptCall->setName("deoptcall");
+    B.CreateRet(DeoptCall);
+  }
+
+  DeoptBlockTerm->eraseFromParent();
+}
+
+bool LowerGuardIntrinsic::runOnFunction(Function &F) {
+  // Check if we can cheaply rule out the possibility of not having any work to
+  // do.
+  auto *GuardDecl = F.getParent()->getFunction(
+      Intrinsic::getName(Intrinsic::experimental_guard));
+  if (!GuardDecl || GuardDecl->use_empty())
+    return false;
+
+  SmallVector<CallInst *, 8> ToLower;
+  for (auto &I : instructions(F))
+    if (auto *CI = dyn_cast<CallInst>(&I))
+      if (auto *F = CI->getCalledFunction())
+        if (F->getIntrinsicID() == Intrinsic::experimental_guard)
+          ToLower.push_back(CI);
+
+  if (ToLower.empty())
+    return false;
+
+  auto *DeoptIntrinsic = Intrinsic::getDeclaration(
+      F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()});
+
+  for (auto *CI : ToLower) {
+    MakeGuardControlFlowExplicit(DeoptIntrinsic, CI);
+    CI->eraseFromParent();
+  }
+
+  return true;
+}
+
+char LowerGuardIntrinsic::ID = 0;
+INITIALIZE_PASS(LowerGuardIntrinsic, "lower-guard-intrinsic",
+                "Lower the guard intrinsic to normal control flow", false,
+                false)
+
+Pass *llvm::createLowerGuardIntrinsicPass() {
+  return new LowerGuardIntrinsic();
+}
diff --git a/llvm/lib/Transforms/Scalar/Scalar.cpp b/llvm/lib/Transforms/Scalar/Scalar.cpp
index 10b14623033..a8c0c14f738 100644
--- a/llvm/lib/Transforms/Scalar/Scalar.cpp
+++ b/llvm/lib/Transforms/Scalar/Scalar.cpp
@@ -62,6 +62,7 @@ void llvm::initializeScalarOpts(PassRegistry &Registry) {
   initializeLoopIdiomRecognizePass(Registry);
   initializeLowerAtomicPass(Registry);
   initializeLowerExpectIntrinsicPass(Registry);
+  initializeLowerGuardIntrinsicPass(Registry);
   initializeMemCpyOptPass(Registry);
   initializeMergedLoadStoreMotionPass(Registry);
   initializeNaryReassociatePass(Registry);
diff --git a/llvm/lib/Transforms/Utils/InlineFunction.cpp b/llvm/lib/Transforms/Utils/InlineFunction.cpp
index 31cf5fbdc85..50eff521318 100644
--- a/llvm/lib/Transforms/Utils/InlineFunction.cpp
+++ b/llvm/lib/Transforms/Utils/InlineFunction.cpp
@@ -428,12 +428,14 @@ static BasicBlock *HandleCallsInBlockInlinedThroughInvoke(
       continue;
 
     // We do not need to (and in fact, cannot) convert possibly throwing calls
-    // to @llvm.experimental_deoptimize into invokes.  The caller's "segment" of
-    // the deoptimization continuation attached to the newly inlined
-    // @llvm.experimental_deoptimize call should contain the exception handling
-    // logic, if any.
+    // to @llvm.experimental_deoptimize (resp. @llvm.experimental.guard) into
+    // invokes.  The caller's "segment" of the deoptimization continuation
+    // attached to the newly inlined @llvm.experimental_deoptimize
+    // (resp. @llvm.experimental.guard) call should contain the exception
+    // handling logic, if any.
     if (auto *F = CI->getCalledFunction())
-      if (F->getIntrinsicID() == Intrinsic::experimental_deoptimize)
+      if (F->getIntrinsicID() == Intrinsic::experimental_deoptimize ||
+          F->getIntrinsicID() == Intrinsic::experimental_guard)
         continue;
 
     if (auto FuncletBundle = CI->getOperandBundle(LLVMContext::OB_funclet)) {