Index: lib/Target/AMDGPU/AMDGPU.h
===================================================================
--- lib/Target/AMDGPU/AMDGPU.h
+++ lib/Target/AMDGPU/AMDGPU.h
@@ -51,6 +51,10 @@
 void initializeAMDGPUAnnotateKernelFeaturesPass(PassRegistry &);
 extern char &AMDGPUAnnotateKernelFeaturesID;
 
+ModulePass *createAMDGPULowerIntrinsicsPass();
+void initializeAMDGPULowerIntrinsicsPass(PassRegistry &);
+extern char &AMDGPULowerIntrinsicsID;
+
 void initializeSIFoldOperandsPass(PassRegistry &);
 extern char &SIFoldOperandsID;
 
Index: lib/Target/AMDGPU/AMDGPUISelLowering.cpp
===================================================================
--- lib/Target/AMDGPU/AMDGPUISelLowering.cpp
+++ lib/Target/AMDGPU/AMDGPUISelLowering.cpp
@@ -451,10 +451,11 @@
 
   PredictableSelectIsExpensive = false;
 
-  // FIXME: Need to really handle these.
-  MaxStoresPerMemcpy  = 4096;
-  MaxStoresPerMemmove = 4096;
-  MaxStoresPerMemset  = 4096;
+  // memcpy/memmove/memset are expanded in the IR, so we shouldn't need to worry
+  // about these during lowering.
+  MaxStoresPerMemcpy  = 0xffffffff;
+  MaxStoresPerMemmove = 0xffffffff;
+  MaxStoresPerMemset  = 0xffffffff;
 
   setTargetDAGCombine(ISD::BITCAST);
   setTargetDAGCombine(ISD::SHL);
Index: lib/Target/AMDGPU/AMDGPULowerIntrinsics.cpp
===================================================================
--- /dev/null
+++ lib/Target/AMDGPU/AMDGPULowerIntrinsics.cpp
@@ -0,0 +1,132 @@
+//===-- AMDGPULowerIntrinsicsPass.cpp -------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AMDGPU.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Transforms/Utils/LowerMemIntrinsics.h"
+
+#include "llvm/Support/Debug.h"
+
+#define DEBUG_TYPE "amdgpu-lower-intrinsics"
+
+using namespace llvm;
+
+namespace {
+
+const unsigned MaxStaticSize = 1024;
+
+class AMDGPULowerIntrinsics : public ModulePass {
+public:
+  static char ID;
+
+  AMDGPULowerIntrinsics() : ModulePass(ID) { }
+  bool runOnModule(Module &M) override;
+  StringRef getPassName() const override {
+    return "AMDGPU Lower Intrinsics";
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesAll();
+    ModulePass::getAnalysisUsage(AU);
+  }
+};
+
+}
+
+char AMDGPULowerIntrinsics::ID = 0;
+
+char &llvm::AMDGPULowerIntrinsicsID = AMDGPULowerIntrinsics::ID;
+
+INITIALIZE_PASS(AMDGPULowerIntrinsics, DEBUG_TYPE,
+                "Lower intrinsics", false, false)
+
+// TODO: Should refine based on estimated number of accesses (e.g. does it
+// require splitting based on alignment)
+static bool shouldExpandOperationWithSize(Value *Size) {
+  ConstantInt *CI = dyn_cast<ConstantInt>(Size);
+  return !CI || (CI->getZExtValue() > MaxStaticSize);
+}
+
+static bool expandMemIntrinsicUses(Function &F) {
+  Intrinsic::ID ID = F.getIntrinsicID();
+  bool Changed;
+
+  for (auto I = F.user_begin(), E = F.user_end(); I != E;) {
+    Instruction *Inst = cast<Instruction>(*I);
+    ++I;
+
+    switch (ID) {
+    case Intrinsic::memcpy: {
+      auto *Memcpy = cast<MemCpyInst>(Inst);
+      if (shouldExpandOperationWithSize(Memcpy->getLength())) {
+        convertMemCpyToLoop(Memcpy);
+        Changed = true;
+        Memcpy->eraseFromParent();
+      }
+
+      break;
+    }
+    case Intrinsic::memmove: {
+      auto *Memmove = cast<MemMoveInst>(Inst);
+      if (shouldExpandOperationWithSize(Memmove->getLength())) {
+        convertMemMoveToLoop(Memmove);
+        Changed = true;
+        Memmove->eraseFromParent();
+      }
+
+      break;
+    }
+    case Intrinsic::memset: {
+      auto *Memset = cast<MemSetInst>(Inst);
+      if (shouldExpandOperationWithSize(Memset->getLength())) {
+        convertMemSetToLoop(Memset);
+        Changed = true;
+        Memset->eraseFromParent();
+      }
+
+      break;
+    }
+    default:
+      break;
+    }
+  }
+
+  return Changed;
+}
+
+bool AMDGPULowerIntrinsics::runOnModule(Module &M) {
+  bool Changed = false;
+
+  dbgs() << "RUnning\n";
+
+  for (Function &F : M) {
+    if (!F.isDeclaration())
+      continue;
+
+    switch (F.getIntrinsicID()) {
+    case Intrinsic::memcpy:
+    case Intrinsic::memmove:
+    case Intrinsic::memset:
+      if (expandMemIntrinsicUses(F))
+        Changed = true;
+      break;
+    default:
+      break;
+    }
+  }
+
+  return Changed;
+}
+
+ModulePass *llvm::createAMDGPULowerIntrinsicsPass() {
+  return new AMDGPULowerIntrinsics();
+}
Index: lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
===================================================================
--- lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
+++ lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
@@ -108,6 +108,7 @@
   initializeSILoadStoreOptimizerPass(*PR);
   initializeAMDGPUAnnotateKernelFeaturesPass(*PR);
   initializeAMDGPUAnnotateUniformValuesPass(*PR);
+  initializeAMDGPULowerIntrinsicsPass(*PR);
   initializeAMDGPUPromoteAllocaPass(*PR);
   initializeAMDGPUCodeGenPreparePass(*PR);
   initializeAMDGPUUnifyMetadataPass(*PR);
@@ -472,6 +473,8 @@
   disablePass(&FuncletLayoutID);
   disablePass(&PatchableFunctionID);
 
+  addPass(createAMDGPULowerIntrinsicsPass());
+
   // Function calls are not supported, so make sure we inline everything.
   addPass(createAMDGPUAlwaysInlinePass());
   addPass(createAlwaysInlinerLegacyPass());
Index: lib/Target/AMDGPU/CMakeLists.txt
===================================================================
--- lib/Target/AMDGPU/CMakeLists.txt
+++ lib/Target/AMDGPU/CMakeLists.txt
@@ -45,6 +45,7 @@
   AMDGPUTargetObjectFile.cpp
   AMDGPUIntrinsicInfo.cpp
   AMDGPUISelDAGToDAG.cpp
+  AMDGPULowerIntrinsics.cpp
   AMDGPUMCInstLower.cpp
   AMDGPUMachineFunction.cpp
   AMDGPUUnifyMetadata.cpp
Index: test/CodeGen/AMDGPU/lower-mem-intrinsics.ll
===================================================================
--- /dev/null
+++ test/CodeGen/AMDGPU/lower-mem-intrinsics.ll
@@ -0,0 +1,117 @@
+; RUN: opt -S -amdgpu-lower-intrinsics %s | FileCheck -check-prefix=OPT %s
+
+declare void @llvm.memcpy.p1i8.p1i8.i64(i8 addrspace(1)* nocapture, i8 addrspace(1)* nocapture readonly, i64, i32, i1) #1
+declare void @llvm.memcpy.p1i8.p3i8.i32(i8 addrspace(1)* nocapture, i8 addrspace(3)* nocapture readonly, i32, i32, i1) #1
+
+declare void @llvm.memmove.p1i8.p1i8.i64(i8 addrspace(1)* nocapture, i8 addrspace(1)* nocapture readonly, i64, i32, i1) #1
+declare void @llvm.memset.p1i8.i64(i8 addrspace(1)* nocapture, i8, i64, i32, i1) #1
+
+; Test the upper bound for sizes to leave
+; OPT-LABEL: @max_size_small_static_memcpy_caller0(
+; OPT: call void @llvm.memcpy.p1i8.p1i8.i64(i8 addrspace(1)* %dst, i8 addrspace(1)* %src, i64 1024, i32 1, i1 false)
+define void @max_size_small_static_memcpy_caller0(i8 addrspace(1)* %dst, i8 addrspace(1)* %src) #0 {
+  call void @llvm.memcpy.p1i8.p1i8.i64(i8 addrspace(1)* %dst, i8 addrspace(1)* %src, i64 1024, i32 1, i1 false)
+  ret void
+}
+
+; Smallest static size which will be expanded
+; OPT-LABEL: @min_size_large_static_memcpy_caller0(
+; OPT-NOT: call
+; OPT: getelementptr
+; OPT-NEXT: load i8
+; OPT: getelementptr
+; OPT-NEXT: store i8
+define void @min_size_large_static_memcpy_caller0(i8 addrspace(1)* %dst, i8 addrspace(1)* %src) #0 {
+  call void @llvm.memcpy.p1i8.p1i8.i64(i8 addrspace(1)* %dst, i8 addrspace(1)* %src, i64 1025, i32 1, i1 false)
+  ret void
+}
+
+; OPT-LABEL: @max_size_small_static_memmove_caller0(
+; OPT: call void @llvm.memmove.p1i8.p1i8.i64(i8 addrspace(1)* %dst, i8 addrspace(1)* %src, i64 1024, i32 1, i1 false)
+define void @max_size_small_static_memmove_caller0(i8 addrspace(1)* %dst, i8 addrspace(1)* %src) #0 {
+  call void @llvm.memmove.p1i8.p1i8.i64(i8 addrspace(1)* %dst, i8 addrspace(1)* %src, i64 1024, i32 1, i1 false)
+  ret void
+}
+
+; OPT-LABEL: @min_size_large_static_memmove_caller0(
+; OPT-NOT: call
+; OPT: getelementptr
+; OPT-NEXT: load i8
+; OPT: getelementptr
+; OPT-NEXT: store i8
+define void @min_size_large_static_memmove_caller0(i8 addrspace(1)* %dst, i8 addrspace(1)* %src) #0 {
+  call void @llvm.memmove.p1i8.p1i8.i64(i8 addrspace(1)* %dst, i8 addrspace(1)* %src, i64 1025, i32 1, i1 false)
+  ret void
+}
+
+; OPT-LABEL: @max_size_small_static_memset_caller0(
+; OPT: call void @llvm.memset.p1i8.i64(i8 addrspace(1)* %dst, i8 %val, i64 1024, i32 1, i1 false)
+define void @max_size_small_static_memset_caller0(i8 addrspace(1)* %dst, i8 %val) #0 {
+  call void @llvm.memset.p1i8.i64(i8 addrspace(1)* %dst, i8 %val, i64 1024, i32 1, i1 false)
+  ret void
+}
+
+; OPT-LABEL: @min_size_large_static_memset_caller0(
+; OPT-NOT: call
+; OPT: getelementptr
+; OPT: store i8
+define void @min_size_large_static_memset_caller0(i8 addrspace(1)* %dst, i8 %val) #0 {
+  call void @llvm.memset.p1i8.i64(i8 addrspace(1)* %dst, i8 %val, i64 1025, i32 1, i1 false)
+  ret void
+}
+
+; OPT-LABEL: @variable_memcpy_caller0(
+; OPT-NOT: call
+; OPT: phi
+define void @variable_memcpy_caller0(i8 addrspace(1)* %dst, i8 addrspace(1)* %src, i64 %n) #0 {
+  call void @llvm.memcpy.p1i8.p1i8.i64(i8 addrspace(1)* %dst, i8 addrspace(1)* %src, i64 %n, i32 1, i1 false)
+  ret void
+}
+
+; OPT-LABEL: @variable_memcpy_caller1(
+; OPT-NOT: call
+; OPT: phi
+define void @variable_memcpy_caller1(i8 addrspace(1)* %dst, i8 addrspace(1)* %src, i64 %n) #0 {
+  call void @llvm.memcpy.p1i8.p1i8.i64(i8 addrspace(1)* %dst, i8 addrspace(1)* %src, i64 %n, i32 1, i1 false)
+  ret void
+}
+
+; OPT-LABEL: @memcpy_multi_use_one_function(
+; OPT-NOT: call
+; OPT: phi
+; OPT-NOT: call
+; OPT: phi
+; OPT-NOT: call
+define void @memcpy_multi_use_one_function(i8 addrspace(1)* %dst0, i8 addrspace(1)* %dst1, i8 addrspace(1)* %src, i64 %n, i64 %m) #0 {
+  call void @llvm.memcpy.p1i8.p1i8.i64(i8 addrspace(1)* %dst0, i8 addrspace(1)* %src, i64 %n, i32 1, i1 false)
+  call void @llvm.memcpy.p1i8.p1i8.i64(i8 addrspace(1)* %dst1, i8 addrspace(1)* %src, i64 %m, i32 1, i1 false)
+  ret void
+}
+
+; OPT-LABEL: @memcpy_alt_type(
+; OPT: phi
+; OPT: getelementptr inbounds i8, i8 addrspace(3)*
+; OPT: load i8, i8 addrspace(3)*
+; OPT: getelementptr inbounds i8, i8 addrspace(1)*
+; OPT: store i8
+define void @memcpy_alt_type(i8 addrspace(1)* %dst, i8 addrspace(3)* %src, i32 %n) #0 {
+  call void @llvm.memcpy.p1i8.p3i8.i32(i8 addrspace(1)* %dst, i8 addrspace(3)* %src, i32 %n, i32 1, i1 false)
+  ret void
+}
+
+; One of the uses in the function should be expanded, the other left alone.
+; OPT-LABEL: @memcpy_multi_use_one_function_keep_small(
+; OPT: getelementptr inbounds i8, i8 addrspace(1)*
+; OPT: load i8, i8 addrspace(1)*
+; OPT: getelementptr inbounds i8, i8 addrspace(1)*
+; OPT: store i8
+
+; OPT: call void @llvm.memcpy.p1i8.p1i8.i64(i8 addrspace(1)* %dst1, i8 addrspace(1)* %src, i64 102, i32 1, i1 false)
+define void @memcpy_multi_use_one_function_keep_small(i8 addrspace(1)* %dst0, i8 addrspace(1)* %dst1, i8 addrspace(1)* %src, i64 %n) #0 {
+  call void @llvm.memcpy.p1i8.p1i8.i64(i8 addrspace(1)* %dst0, i8 addrspace(1)* %src, i64 %n, i32 1, i1 false)
+  call void @llvm.memcpy.p1i8.p1i8.i64(i8 addrspace(1)* %dst1, i8 addrspace(1)* %src, i64 102, i32 1, i1 false)
+  ret void
+}
+
+attributes #0 = { nounwind }
+attributes #1 = { argmemonly nounwind }