Index: tools/llvm-exegesis/lib/Assembler.cpp
===================================================================
--- tools/llvm-exegesis/lib/Assembler.cpp
+++ tools/llvm-exegesis/lib/Assembler.cpp
@@ -9,6 +9,7 @@
 
 #include "Assembler.h"
 
+#include "Target.h"
 #include "llvm/CodeGen/GlobalISel/CallLowering.h"
 #include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
@@ -139,6 +140,8 @@
   auto &Properties = MF.getProperties();
   Properties.set(llvm::MachineFunctionProperties::Property::NoVRegs);
   Properties.reset(llvm::MachineFunctionProperties::Property::IsSSA);
+  // FIXME: Remove this when we assign all used registers as config step. This
+  // essentially disables checks that used registers are def'ed somewhere.
   Properties.reset(llvm::MachineFunctionProperties::Property::TracksLiveness);
   // prologue/epilogue pass needs the reserved registers to be frozen, this
   // is usually done by the SelectionDAGISel pass.
@@ -158,6 +161,11 @@
   PM.add(TPC);
   PM.add(MMI.release());
   TPC->printAndVerify("MachineFunctionGenerator::assemble");
+  // Add target-specific passes.
+  if (const auto *ET = ExegesisTarget::lookup(TM->getTargetTriple())) {
+    ET->addTargetSpecificPasses(PM);
+    TPC->printAndVerify("After ExegesisTarget::addTargetSpecificPasses");
+  }
   // Adding the following passes:
   // - machineverifier: checks that the MachineFunction is well formed.
   // - prologepilog: saves and restore callee saved registers.
Index: tools/llvm-exegesis/lib/Target.h
===================================================================
--- tools/llvm-exegesis/lib/Target.h
+++ tools/llvm-exegesis/lib/Target.h
@@ -18,14 +18,19 @@
 #define LLVM_TOOLS_LLVM_EXEGESIS_TARGET_H
 
 #include "llvm/ADT/Triple.h"
+#include "llvm/CodeGen/TargetPassConfig.h"
+#include "llvm/IR/LegacyPassManager.h"
 
 namespace exegesis {
 
 class ExegesisTarget {
 public:
+  // Targets can use this to add target-specific passes in assembleToStream();
+  virtual void addTargetSpecificPasses(llvm::PassManagerBase &PM) const {}
+
   // Returns the ExegesisTarget for the given triple or nullptr if the target
   // does not exist.
-  static const ExegesisTarget* lookup(llvm::StringRef TT);
+  static const ExegesisTarget *lookup(llvm::Triple TT);
   // Registers a target. Not thread safe.
   static void registerTarget(ExegesisTarget *T);
 
Index: tools/llvm-exegesis/lib/Target.cpp
===================================================================
--- tools/llvm-exegesis/lib/Target.cpp
+++ tools/llvm-exegesis/lib/Target.cpp
@@ -14,10 +14,10 @@
 
 static ExegesisTarget* FirstTarget = nullptr;
 
-const ExegesisTarget* ExegesisTarget::lookup(llvm::StringRef TT) {
-  const llvm::Triple::ArchType Arch = llvm::Triple(TT).getArch();
+const ExegesisTarget *ExegesisTarget::lookup(llvm::Triple TT) {
   for (const ExegesisTarget* T = FirstTarget; T != nullptr; T = T->Next) {
-    if (T->matchesArch(Arch)) return T;
+    if (T->matchesArch(TT.getArch()))
+      return T;
   }
   return nullptr;
 }
Index: tools/llvm-exegesis/lib/X86/CMakeLists.txt
===================================================================
--- tools/llvm-exegesis/lib/X86/CMakeLists.txt
+++ tools/llvm-exegesis/lib/X86/CMakeLists.txt
@@ -1,3 +1,8 @@
+include_directories(
+  ${LLVM_MAIN_SRC_DIR}/lib/Target/X86
+  ${LLVM_BINARY_DIR}/lib/Target/X86
+  )
+
 add_library(LLVMExegesisX86
   STATIC
   Target.cpp
Index: tools/llvm-exegesis/lib/X86/Target.cpp
===================================================================
--- tools/llvm-exegesis/lib/X86/Target.cpp
+++ tools/llvm-exegesis/lib/X86/Target.cpp
@@ -8,12 +8,20 @@
 //===----------------------------------------------------------------------===//
 #include "../Target.h"
 
+#include "X86.h"
+
 namespace exegesis {
 
 namespace {
 
 class ExegesisX86Target : public ExegesisTarget {
-private:
+  void addTargetSpecificPasses(llvm::PassManagerBase &PM) const override {
+    // Lowers FP pseudo-instructions, e.g. ABS_Fp32 -> ABS_F.
+    // FIXME: Enable when the exegesis assembler no longer does
+    // Properties.reset(TracksLiveness);
+    // PM.add(llvm::createX86FloatingPointStackifierPass());
+  }
+
   bool matchesArch(llvm::Triple::ArchType Arch) const override {
     return Arch == llvm::Triple::x86_64 || Arch == llvm::Triple::x86;
   }
Index: unittests/tools/llvm-exegesis/X86/TargetTest.cpp
===================================================================
--- unittests/tools/llvm-exegesis/X86/TargetTest.cpp
+++ unittests/tools/llvm-exegesis/X86/TargetTest.cpp
@@ -20,7 +20,8 @@
 };
 
 TEST_F(X86TargetTest, Lookup) {
-  EXPECT_THAT(ExegesisTarget::lookup("x86_64-unknown-linux"), NotNull());
+  EXPECT_THAT(ExegesisTarget::lookup(llvm::Triple("x86_64-unknown-linux")),
+              NotNull());
 }
 
 } // namespace