diff --git a/llvm/include/llvm/CodeGen/CodeGenPassBuilder.h b/llvm/include/llvm/CodeGen/CodeGenPassBuilder.h
--- a/llvm/include/llvm/CodeGen/CodeGenPassBuilder.h
+++ b/llvm/include/llvm/CodeGen/CodeGenPassBuilder.h
@@ -731,6 +731,7 @@
 void CodeGenPassBuilder<Derived>::addISelPrepare(AddIRPass &addPass) const {
   derived().addPreISel(addPass);
 
+  //addPass(CallBrPrepare()); // TODO(ndesaulniers): impl pass
   // Add both the safe stack and the stack protection passes: each of them will
   // only protect functions that have corresponding attributes.
   addPass(SafeStackPass());
diff --git a/llvm/include/llvm/CodeGen/MachinePassRegistry.def b/llvm/include/llvm/CodeGen/MachinePassRegistry.def
--- a/llvm/include/llvm/CodeGen/MachinePassRegistry.def
+++ b/llvm/include/llvm/CodeGen/MachinePassRegistry.def
@@ -123,6 +123,7 @@
 DUMMY_FUNCTION_PASS("cfguard-check", CFGuardCheckPass, ())
 DUMMY_FUNCTION_PASS("gc-info-printer", GCInfoPrinterPass, ())
 DUMMY_FUNCTION_PASS("select-optimize", SelectOptimizePass, ())
+DUMMY_FUNCTION_PASS("callbrprepare", CallBrPrepare, ())
 #undef DUMMY_FUNCTION_PASS
 
 #ifndef DUMMY_MODULE_PASS
diff --git a/llvm/include/llvm/CodeGen/Passes.h b/llvm/include/llvm/CodeGen/Passes.h
--- a/llvm/include/llvm/CodeGen/Passes.h
+++ b/llvm/include/llvm/CodeGen/Passes.h
@@ -583,6 +583,8 @@
 
   /// This pass converts conditional moves to conditional jumps when profitable.
   FunctionPass *createSelectOptimizePass();
+
+  FunctionPass *createCallBrPass();
 } // End llvm namespace
 
 #endif
diff --git a/llvm/include/llvm/InitializePasses.h b/llvm/include/llvm/InitializePasses.h
--- a/llvm/include/llvm/InitializePasses.h
+++ b/llvm/include/llvm/InitializePasses.h
@@ -86,6 +86,7 @@
 void initializeCFIInstrInserterPass(PassRegistry&);
 void initializeCFLAndersAAWrapperPassPass(PassRegistry&);
 void initializeCFLSteensAAWrapperPassPass(PassRegistry&);
+void initializeCallBrPreparePass(PassRegistry&);
 void initializeCallGraphDOTPrinterPass(PassRegistry&);
 void initializeCallGraphPrinterLegacyPassPass(PassRegistry&);
 void initializeCallGraphViewerPass(PassRegistry&);
diff --git a/llvm/lib/CodeGen/CMakeLists.txt b/llvm/lib/CodeGen/CMakeLists.txt
--- a/llvm/lib/CodeGen/CMakeLists.txt
+++ b/llvm/lib/CodeGen/CMakeLists.txt
@@ -35,6 +35,7 @@
   BasicBlockSections.cpp
   BasicBlockSectionsProfileReader.cpp
   CalcSpillWeights.cpp
+  CallBrPrepare.cpp
   CallingConvLower.cpp
   CFGuardLongjmp.cpp
   CFIFixup.cpp
diff --git a/llvm/lib/CodeGen/CallBrPrepare.cpp b/llvm/lib/CodeGen/CallBrPrepare.cpp
new file mode 100644
--- /dev/null
+++ b/llvm/lib/CodeGen/CallBrPrepare.cpp
@@ -0,0 +1,66 @@
+//===-- CallBrPrepare - Prepare callbr for code generation ----------------===//
+//
+// 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 lowers callbrs in LLVM IR to something closer that the backend can
+// perform correct instruction selection for.  In particular, callbr may have
+// inline asm with output constraints that require specific physical registers.
+// These physical register will need to be copied back to virtual registers
+// somewhere. If we have critical edges, we may need to split them. Regardless
+// of critical edges, we create distinct new SSA values for each indirect
+// destination of the callbr, then remap users of the direct destinations value
+// which aren't dominated by the direct destination, but are by the indirect
+// destination.
+//
+// This enables us to keep the use of the callbr's Value simple in IR, and
+// expand control flow when necessary at the last minute before instruction
+// selection.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "callbrprepare"
+
+namespace {
+
+class CallBrPrepare : public FunctionPass {
+public:
+  CallBrPrepare() : FunctionPass(ID) {}
+  static char ID;
+  void getAnalysisUsage(AnalysisUsage &AU) const override;
+  bool runOnFunction(Function &Fn) override;
+};
+
+} // end anonymous namespace
+
+char CallBrPrepare::ID = 0;
+INITIALIZE_PASS(CallBrPrepare, DEBUG_TYPE, "Prepare callbr", false, false)
+
+FunctionPass *llvm::createCallBrPass() { return new CallBrPrepare(); }
+
+void CallBrPrepare::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.setPreservesAll();
+}
+
+bool CallBrPrepare::runOnFunction(Function &Fn) {
+  for (BasicBlock &BB : Fn) {
+    auto *CBR = dyn_cast<CallBrInst>(BB.getTerminator());
+    if (!CBR)
+      continue;
+    // TODO: something interesting.
+    // https://discourse.llvm.org/t/rfc-syncing-asm-goto-with-outputs-with-gcc/65453/8
+  }
+  return false;
+}
diff --git a/llvm/lib/CodeGen/CodeGen.cpp b/llvm/lib/CodeGen/CodeGen.cpp
--- a/llvm/lib/CodeGen/CodeGen.cpp
+++ b/llvm/lib/CodeGen/CodeGen.cpp
@@ -24,6 +24,7 @@
   initializeBasicBlockSectionsPass(Registry);
   initializeBranchFolderPassPass(Registry);
   initializeBranchRelaxationPass(Registry);
+  initializeCallBrPreparePass(Registry);
   initializeCFGuardLongjmpPass(Registry);
   initializeCFIFixupPass(Registry);
   initializeCFIInstrInserterPass(Registry);
diff --git a/llvm/lib/CodeGen/TargetPassConfig.cpp b/llvm/lib/CodeGen/TargetPassConfig.cpp
--- a/llvm/lib/CodeGen/TargetPassConfig.cpp
+++ b/llvm/lib/CodeGen/TargetPassConfig.cpp
@@ -1007,6 +1007,8 @@
   if (requiresCodeGenSCCOrder())
     addPass(new DummyCGSCCPass);
 
+  //addPass(createCallBrPass()); // TODO(ndesaulniers): impl pass
+
   // Add both the safe stack and the stack protection passes: each of them will
   // only protect functions that have corresponding attributes.
   addPass(createSafeStackPass());
diff --git a/llvm/test/CodeGen/AArch64/callbr-prepare.ll b/llvm/test/CodeGen/AArch64/callbr-prepare.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/callbr-prepare.ll
@@ -0,0 +1,30 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt %s -callbrprepare -S -o - | FileCheck %s
+
+; TODO: update this test to split critical edges.
+define i32 @test0() {
+; CHECK-LABEL: @test0(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[OUT:%.*]] = callbr i32 asm "# $0", "=r,!i"()
+; CHECK-NEXT:    to label [[DIRECT:%.*]] [label %indirect]
+; CHECK:       direct:
+; CHECK-NEXT:    [[OUT2:%.*]] = callbr i32 asm "# $0", "=r,!i"()
+; CHECK-NEXT:    to label [[DIRECT2:%.*]] [label %indirect]
+; CHECK:       direct2:
+; CHECK-NEXT:    ret i32 0
+; CHECK:       indirect:
+; CHECK-NEXT:    [[OUT3:%.*]] = phi i32 [ [[OUT]], [[ENTRY:%.*]] ], [ [[OUT2]], [[DIRECT]] ]
+; CHECK-NEXT:    ret i32 [[OUT3]]
+;
+entry:
+  %out = callbr i32 asm "# $0", "=r,!i"()
+  to label %direct [label %indirect]
+direct:
+  %out2 = callbr i32 asm "# $0", "=r,!i"()
+  to label %direct2 [label %indirect]
+direct2:
+  ret i32 0
+indirect:
+  %out3 = phi i32 [%out, %entry], [%out2, %direct]
+  ret i32 %out3
+}
diff --git a/llvm/tools/opt/opt.cpp b/llvm/tools/opt/opt.cpp
--- a/llvm/tools/opt/opt.cpp
+++ b/llvm/tools/opt/opt.cpp
@@ -387,7 +387,8 @@
       "view-regions",         "view-regions-only",
       "select-optimize",      "expand-large-div-rem",
       "structurizecfg",       "fix-irreducible",
-      "expand-large-fp-convert"};
+      "expand-large-fp-convert", "callbrprepare",
+  };
   for (const auto &P : PassNamePrefix)
     if (Pass.startswith(P))
       return true;
@@ -438,6 +439,7 @@
   initializeExpandMemCmpPassPass(Registry);
   initializeScalarizeMaskedMemIntrinLegacyPassPass(Registry);
   initializeSelectOptimizePass(Registry);
+  initializeCallBrPreparePass(Registry);
   initializeCodeGenPreparePass(Registry);
   initializeAtomicExpandPass(Registry);
   initializeRewriteSymbolsLegacyPassPass(Registry);
diff --git a/llvm/utils/gn/secondary/llvm/lib/CodeGen/BUILD.gn b/llvm/utils/gn/secondary/llvm/lib/CodeGen/BUILD.gn
--- a/llvm/utils/gn/secondary/llvm/lib/CodeGen/BUILD.gn
+++ b/llvm/utils/gn/secondary/llvm/lib/CodeGen/BUILD.gn
@@ -33,6 +33,7 @@
     "CFIFixup.cpp",
     "CFIInstrInserter.cpp",
     "CalcSpillWeights.cpp",
+    "CallBrPrepare.cpp",
     "CallingConvLower.cpp",
     "CodeGen.cpp",
     "CodeGenCommonISel.cpp",