Index: clang/lib/CodeGen/BackendUtil.cpp
===================================================================
--- clang/lib/CodeGen/BackendUtil.cpp
+++ clang/lib/CodeGen/BackendUtil.cpp
@@ -1440,6 +1440,12 @@
   Conf.OptLevel = CGOpts.OptimizationLevel;
   initTargetOptions(Conf.Options, CGOpts, TOpts, LOpts, HeaderOpts);
   Conf.SampleProfile = std::move(SampleProfile);
+  Conf.PTO.LoopUnrolling = CGOpts.UnrollLoops;
+  // For historical reasons, loop interleaving is set to mirror setting for loop
+  // unrolling.
+  Conf.PTO.LoopInterleaving = CGOpts.UnrollLoops;
+  Conf.PTO.LoopVectorization = CGOpts.VectorizeLoop;
+  Conf.PTO.SLPVectorization = CGOpts.VectorizeSLP;
 
   // Context sensitive profile.
   if (CGOpts.hasProfileCSIRInstr()) {
Index: clang/test/CodeGen/thinlto-debug-pm.c
===================================================================
--- clang/test/CodeGen/thinlto-debug-pm.c
+++ clang/test/CodeGen/thinlto-debug-pm.c
@@ -13,5 +13,16 @@
 // O2-OLDPM: Loop Vectorization
 // O0-OLDPM-NOT: Loop Vectorization
 
+// Test to ensure the SLP flag is passed down to the ThinLTO backend.
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-obj -O2 -vectorize-slp
+// -mllvm -vectorize-slp=false -mllvm -vectorize-loops=false -o %t2.o -x ir %t.o
+// -fthinlto-index=%t.thinlto.bc -fdebug-pass-manager
+// -fexperimental-new-pass-manager 2>&1 | FileCheck %s --check-prefix=O2-SLP
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-obj -O0 -vectorize-slp
+// -o %t2.o -x ir %t.o -fthinlto-index=%t.thinlto.bc -fdebug-pass-manager
+// -fexperimental-new-pass-manager 2>&1 | FileCheck %s --check-prefix=O0-SLP
+// O2-SLP: Running pass: SLPVectorizerPass
+// O0-SLP-NOT: Running pass: SLPVectorizerPass
+
 void foo() {
 }
Index: llvm/include/llvm/LTO/Config.h
===================================================================
--- llvm/include/llvm/LTO/Config.h
+++ llvm/include/llvm/LTO/Config.h
@@ -16,6 +16,7 @@
 
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/LLVMContext.h"
+#include "llvm/Passes/PassBuilder.h"
 #include "llvm/Support/CodeGen.h"
 #include "llvm/Target/TargetOptions.h"
 
@@ -126,6 +127,8 @@
   /// with llvm-lto2.
   std::unique_ptr<raw_ostream> ResolutionFile;
 
+  PipelineTuningOptions PTO;
+
   /// The following callbacks deal with tasks, which normally represent the
   /// entire optimization and code generation pipeline for what will become a
   /// single native object file. Each task has a unique identifier between 0 and
Index: llvm/lib/LTO/LTOBackend.cpp
===================================================================
--- llvm/lib/LTO/LTOBackend.cpp
+++ llvm/lib/LTO/LTOBackend.cpp
@@ -169,7 +169,7 @@
   PassInstrumentationCallbacks PIC;
   StandardInstrumentations SI;
   SI.registerCallbacks(PIC);
-  PassBuilder PB(TM, PipelineTuningOptions(),PGOOpt, &PIC);
+  PassBuilder PB(TM, Conf.PTO, PGOOpt, &PIC);
   AAManager AA;
 
   // Parse a custom AA pipeline if asked to.
Index: llvm/tools/llvm-lto2/CMakeLists.txt
===================================================================
--- llvm/tools/llvm-lto2/CMakeLists.txt
+++ llvm/tools/llvm-lto2/CMakeLists.txt
@@ -9,6 +9,7 @@
   LTO
   MC
   Object
+  Passes
   Support
   Target
   )