Re-committing r275284: add support to inline __builtin_mempcpy

Patch by Sunita Marathe

Differential Revision: http://reviews.llvm.org/D21920

llvm-svn: 276771

2 files changed, 48 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index e03282cad6b..af86d876813 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -6044,6 +6044,49 @@ 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) {
+
+  // Verify argument count: void *mempcpy(void *, const void *, size_t)
+  if (I.getNumArgOperands() != 3)
+    return false;
+
+  SDValue Dst = getValue(I.getArgOperand(0));
+  SDValue Src = getValue(I.getArgOperand(1));
+  SDValue Size = getValue(I.getArgOperand(2));
+
+  unsigned DstAlign = DAG.InferPtrAlignment(Dst);
+  unsigned SrcAlign = DAG.InferPtrAlignment(Src);
+  unsigned Align = std::min(DstAlign, SrcAlign);
+  if (Align == 0) // Alignment of one or both could not be inferred.
+    Align = 1; // 0 and 1 both specify no alignment, but 0 is reserved.
+
+  bool isVol = false;
+  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);
+
+  // Check if Size needs to be truncated or extended.
+  Size = DAG.getSExtOrTrunc(Size, sdl, Dst.getValueType());
+
+  // 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.
@@ -6334,6 +6377,10 @@ 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;
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
index b9888ae8763..18c39d0fccb 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
@@ -885,6 +885,7 @@ private:
   void visitPHI(const PHINode &I);
   void visitCall(const CallInst &I);
   bool visitMemCmpCall(const CallInst &I);
+  bool visitMemPCpyCall(const CallInst &I);
   bool visitMemChrCall(const CallInst &I);
   bool visitStrCpyCall(const CallInst &I, bool isStpcpy);
   bool visitStrCmpCall(const CallInst &I);