diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -5099,6 +5099,16 @@
 
   return PPCISD::CALL;
 }
+
+static bool isValidAIXExternalSymSDNode(StringRef SymName) {
+  return StringSwitch<bool>(SymName)
+      .Cases("__divdi3", "__fixdfdi", "__fixunsdfdi", "__floatdidf",
+             "__floatdisf", "__floatundidf", "__floatundisf", "__moddi3",
+             "__udivdi3", "__umoddi3", true)
+      .Cases("ceil", "floor", "memcpy", "memmove", "memset", "round", true)
+      .Default(false);
+}
+
 static SDValue transformCallee(const SDValue &Callee, SelectionDAG &DAG,
                                const SDLoc &dl, const PPCSubtarget &Subtarget) {
   if (!Subtarget.usesFunctionDescriptors() && !Subtarget.isELFv2ABI())
@@ -5123,42 +5133,70 @@
       Subtarget.is32BitELFABI() && !isLocalCallee() &&
       Subtarget.getTargetMachine().getRelocationModel() == Reloc::PIC_;
 
+  // On AIX, direct function calls reference the symbol for the function's
+  // entry point, which is named by prepending a "." before the function's
+  // C-linkage name.
+  const auto getAIXFuncEntryPointSymbol =
+      [&](StringRef FuncName, bool IsDeclaration,
+          const XCOFF::StorageClass &SC) {
+        auto &Context = DAG.getMachineFunction().getMMI().getContext();
+
+        MCSymbolXCOFF *S = cast<MCSymbolXCOFF>(
+            Context.getOrCreateSymbol(Twine(".") + Twine(FuncName)));
+
+        if (IsDeclaration && !S->hasContainingCsect()) {
+          // On AIX, an undefined symbol needs to be associated with a
+          // MCSectionXCOFF to get the correct storage mapping class.
+          // In this case, XCOFF::XMC_PR.
+          MCSectionXCOFF *Sec = Context.getXCOFFSection(
+              S->getName(), XCOFF::XMC_PR, XCOFF::XTY_ER, SC,
+              SectionKind::getMetadata());
+          S->setContainingCsect(Sec);
+        }
+
+        // Replace the callee SDNode with the MCSymbolSDNode.
+        MVT PtrVT =
+            DAG.getTargetLoweringInfo().getPointerTy(DAG.getDataLayout());
+        return DAG.getMCSymbol(S, PtrVT);
+      };
+
   if (isFunctionGlobalAddress(Callee)) {
     const GlobalAddressSDNode *G = cast<GlobalAddressSDNode>(Callee);
+    const GlobalObject *GO = cast<GlobalObject>(G->getGlobal());
+
     if (!Subtarget.isAIXABI())
-      return DAG.getTargetGlobalAddress(G->getGlobal(), dl,
-                                        Callee.getValueType(), 0,
+      return DAG.getTargetGlobalAddress(GO, dl, Callee.getValueType(), 0,
                                         UsePlt ? PPCII::MO_PLT : 0);
 
-    // On AIX, direct function calls reference the symbol for the function's
-    // entry point, which is named by prepending a "." before the function's
-    // C-linkage name.
-    auto &Context = DAG.getMachineFunction().getMMI().getContext();
+    const XCOFF::StorageClass SC =
+        TargetLoweringObjectFileXCOFF::getStorageClassForGlobal(GO);
+    return getAIXFuncEntryPointSymbol(GO->getName(), GO->isDeclaration(), SC);
+  }
 
-    const GlobalObject *GO = cast<GlobalObject>(G->getGlobal());
-    MCSymbolXCOFF *S = cast<MCSymbolXCOFF>(
-        Context.getOrCreateSymbol(Twine(".") + Twine(GO->getName())));
+  if (ExternalSymbolSDNode *S = dyn_cast<ExternalSymbolSDNode>(Callee)) {
+    const char *SymName = S->getSymbol();
+    if (!Subtarget.isAIXABI()) 
+      return DAG.getTargetExternalSymbol(SymName, Callee.getValueType(),
+                                         UsePlt ? PPCII::MO_PLT : 0);
 
-    if (GO && GO->isDeclaration() && !S->hasContainingCsect()) {
-      // On AIX, an undefined symbol needs to be associated with a
-      // MCSectionXCOFF to get the correct storage mapping class.
-      // In this case, XCOFF::XMC_PR.
+    // If there exists user-defined function whose name is the same as the
+    // ExternalSymbol's, we pick up user-defined version.
+    const Module *Mod = DAG.getMachineFunction().getFunction().getParent();
+    if (const GlobalValue *GV = Mod->getNamedValue(SymName)) {
+      const GlobalObject *GO = dyn_cast<GlobalObject>(GV);
       const XCOFF::StorageClass SC =
           TargetLoweringObjectFileXCOFF::getStorageClassForGlobal(GO);
-      MCSectionXCOFF *Sec =
-          Context.getXCOFFSection(S->getName(), XCOFF::XMC_PR, XCOFF::XTY_ER,
-                                  SC, SectionKind::getMetadata());
-      S->setContainingCsect(Sec);
-    }
-
-    EVT PtrVT = DAG.getTargetLoweringInfo().getPointerTy(DAG.getDataLayout());
-    return DAG.getMCSymbol(S, PtrVT);
+      return getAIXFuncEntryPointSymbol(GO->getName(), GO->isDeclaration(), SC);
+    } else {
+      // TODO: Remove this when the support for ExternalSymbolSDNode is complete.
+      if (isValidAIXExternalSymSDNode(SymName)) {
+        return getAIXFuncEntryPointSymbol(SymName, true, XCOFF::C_EXT);
+      } else {
+        report_fatal_error("Unexpected ExternalSymbolSDNode: " + Twine(SymName));
+      }
+    }  
   }
 
-  if (ExternalSymbolSDNode *S = dyn_cast<ExternalSymbolSDNode>(Callee))
-    return DAG.getTargetExternalSymbol(S->getSymbol(), Callee.getValueType(),
-                                       UsePlt ? PPCII::MO_PLT : 0);
-
   // No transformation needed.
   assert(Callee.getNode() && "What no callee?");
   return Callee;
diff --git a/llvm/test/CodeGen/PowerPC/aix-external-sym-sdnode-lowering.ll b/llvm/test/CodeGen/PowerPC/aix-external-sym-sdnode-lowering.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/aix-external-sym-sdnode-lowering.ll
@@ -0,0 +1,152 @@
+; RUN: llc -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff \
+; RUN: -stop-after=machine-cp < %s | FileCheck \
+; RUN: --check-prefix=32BIT %s
+
+; RUN: llc -verify-machineinstrs -mtriple powerpc64-ibm-aix-xcoff \
+; RUN: -stop-after=machine-cp < %s | FileCheck \
+; RUN: --check-prefix=64BIT %s
+
+define i64 @call_divdi3(i64 %p, i64 %num) {
+entry:
+  %div = sdiv i64 %p, %num
+  ret i64 %div
+}
+
+; 32BIT: BL_NOP <mcsymbol .__divdi3>
+
+define i64 @call_fixdfdi(double %p) {
+entry:
+  %conv = fptosi double %p to i64
+  ret i64 %conv
+}
+
+; 32BIT: BL_NOP <mcsymbol .__fixdfdi>
+
+define i64 @call_fixunsdfdi(double %p) {
+entry:
+  %conv = fptoui double %p to i64
+  ret i64 %conv
+}
+
+; 32BIT: BL_NOP <mcsymbol .__fixunsdfdi>
+
+define double @call_floatdidf(i64 %p) {
+entry:
+  %conv = sitofp i64 %p to double
+  ret double %conv
+}
+
+; 32BIT: BL_NOP <mcsymbol .__floatdidf>
+
+define float @call_floatdisf(i64 %p) {
+entry:
+  %conv = sitofp i64 %p to float
+  ret float %conv
+}
+
+; 32BIT: BL_NOP <mcsymbol .__floatdisf>
+
+define double @call_floatundidf(i64 %p) {
+entry:
+  %conv = uitofp i64 %p to double
+  ret double %conv
+}
+
+; 32BIT: BL_NOP <mcsymbol .__floatundidf>
+
+define float @call_floatundisf(i64 %p) {
+entry:
+  %conv = uitofp i64 %p to float
+  ret float %conv
+}
+
+; 32BIT: BL_NOP <mcsymbol .__floatundisf>
+
+define i64 @call_moddi3(i64 %p, i64 %num) {
+entry:
+  %rem = srem i64 %p, %num
+  ret i64 %rem
+}
+
+; 32BIT: BL_NOP <mcsymbol .__moddi3>
+
+define i64 @call_udivdi3(i64 %p, i64 %q) {
+  %1 = udiv i64 %p, %q
+  ret i64 %1
+}
+
+; 32BIT: BL_NOP <mcsymbol .__udivdi3>
+
+define i64 @call_umoddi3(i64 %p, i64 %num) {
+entry:
+  %rem = urem i64 %p, %num
+  ret i64 %rem
+}
+
+; 32BIT: BL_NOP <mcsymbol .__umoddi3>
+
+define double @call_ceil(double %n) {
+entry:
+  %0 = call double @llvm.ceil.f64(double %n)
+  ret double %0
+}
+
+declare double @llvm.ceil.f64(double)
+
+; 32BIT: BL_NOP <mcsymbol .ceil>
+; 64BIT: BL8_NOP <mcsymbol .ceil>
+
+define double @call_floor(double %n) {
+entry:
+  %0 = call double @llvm.floor.f64(double %n)
+  ret double %0
+}
+
+declare double @llvm.floor.f64(double)
+
+; 32BIT: BL_NOP <mcsymbol .floor>
+; 64BIT: BL8_NOP <mcsymbol .floor>
+
+define void @call_memcpy(i8* %p, i8* %q, i32 %n) {
+entry:
+  call void @llvm.memcpy.p0i8.p0i8.i32(i8* %p, i8* %q, i32 %n, i1 false)
+  ret void
+}
+
+declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture writeonly, i8* nocapture readonly, i32, i1)
+
+; 32BIT: BL_NOP <mcsymbol .memcpy>
+; 64BIT: BL8_NOP <mcsymbol .memcpy>
+
+define void @call_memmove(i8* %p, i8* %q, i32 %n) {
+entry:
+  call void @llvm.memmove.p0i8.p0i8.i32(i8* %p, i8* %q, i32 %n, i1 false)
+  ret void
+}
+
+declare void @llvm.memmove.p0i8.p0i8.i32(i8* nocapture, i8* nocapture readonly, i32, i1)
+
+; 32BIT: BL_NOP <mcsymbol .memmove>
+; 64BIT: BL8_NOP <mcsymbol .memmove>
+
+define void @call_memset(i8* %p, i8 %q, i32 %n) #0 {
+entry:
+  call void @llvm.memset.p0i8.i32(i8* %p, i8 %q, i32 %n, i1 false)
+  ret void
+}
+
+declare void @llvm.memset.p0i8.i32(i8* nocapture, i8, i32, i1)
+
+; 32BIT: BL_NOP <mcsymbol .memset>
+; 64BIT: BL8_NOP <mcsymbol .memset>
+
+define double @call_round(double %n) {
+entry:
+  %0 = call double @llvm.round.f64(double %n)
+  ret double %0
+}
+
+declare double @llvm.round.f64(double)
+
+; 32BIT: BL_NOP <mcsymbol .round>
+; 64BIT: BL8_NOP <mcsymbol .round>
diff --git a/llvm/test/CodeGen/PowerPC/aix-user-defined-memcpy.ll b/llvm/test/CodeGen/PowerPC/aix-user-defined-memcpy.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/aix-user-defined-memcpy.ll
@@ -0,0 +1,22 @@
+; RUN: llc -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff -mcpu=pwr4 \
+; RUN: -mattr=-altivec < %s | FileCheck --check-prefix=CHECK %s
+
+; RUN: llc -verify-machineinstrs -mtriple powerpc64-ibm-aix-xcoff -mcpu=pwr4 \
+; RUN: -mattr=-altivec < %s | FileCheck --check-prefix=CHECK %s
+
+define dso_local signext i32 @memcpy(i8* %destination, i32 signext %num) {
+entry:
+  ret i32 3
+}
+
+define void @call_memcpy(i8* %p, i8* %q, i32 %n) {
+entry:
+  call void @llvm.memcpy.p0i8.p0i8.i32(i8* %p, i8* %q, i32 %n, i1 false)
+  ret void
+}
+
+declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture writeonly, i8* nocapture readonly, i32, i1)
+
+; CHECK: bl .memcpy
+; CHECK-NOT: error
+; CHECK-NOT: warning