1 files changed, 46 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 27ee96dfedf..26c81e9768d 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -6039,6 +6039,48 @@ bool SelectionDAGBuilder::visitMemChrCall(const CallInst &I) {
   return false;
 }
 
+///
+/// visitMemPCpyCall -- lower a mempcpy call as a memcpy followed by code to
+/// to adjust the dst pointer by the size of the copied memory.
+bool SelectionDAGBuilder::visitMemPCpyCall(const CallInst &I) {
+
+  unsigned int NumOperands = I.getNumArgOperands();
+  if (NumOperands < 3 || NumOperands > 5)
+    return false;
+
+  SDValue Dst = getValue(I.getArgOperand(0));
+  SDValue Src = getValue(I.getArgOperand(1));
+  SDValue Size = getValue(I.getArgOperand(2));
+
+  unsigned Align = 0;
+  if (NumOperands >= 4)
+    Align = cast<ConstantInt>(I.getArgOperand(3))->getZExtValue();
+  if (!Align)
+    Align = 1; // @llvm.memcpy defines 0 and 1 to both mean no alignment.
+
+  bool isVol = false;
+  if (NumOperands == 5)
+    isVol = cast<ConstantInt>(I.getArgOperand(4))->getZExtValue();
+
+  SDLoc sdl = getCurSDLoc();
+  // In the mempcpy context we need to pass in a false value for isTailCall
+  // because the return pointer needs to be adjusted by the size of
+  // the copied memory.
+  SDValue MC = DAG.getMemcpy(getRoot(), sdl, Dst, Src, Size, Align, isVol,
+                             false, /*isTailCall=*/false,
+                             MachinePointerInfo(I.getArgOperand(0)),
+                             MachinePointerInfo(I.getArgOperand(1)));
+  assert(MC.getNode() != nullptr &&
+         "** memcpy should not be lowered as TailCall in mempcpy context **");
+  DAG.setRoot(MC);
+
+  // Adjust return pointer to point just past the last dst byte.
+  SDValue DstPlusSize = DAG.getNode(ISD::ADD, sdl, Dst.getValueType(),
+                                    Dst, Size);
+  setValue(&I, DstPlusSize);
+  return true;
+}
+
 /// visitStrCpyCall -- See if we can lower a strcpy or stpcpy call into an
 /// optimized form.  If so, return true and lower it, otherwise return false
 /// and it will be lowered like a normal call.
@@ -6329,6 +6371,10 @@ void SelectionDAGBuilder::visitCall(const CallInst &I) {
         if (visitMemCmpCall(I))
           return;
         break;
+      case LibFunc::mempcpy:
+        if (visitMemPCpyCall(I))
+          return;
+        break;
       case LibFunc::memchr:
         if (visitMemChrCall(I))
           return;