diff --git a/examples_ptx/mergeSort/Makefile_gpu b/examples_ptx/mergeSort/Makefile_gpu
index 0002b279..79914c2c 100644
--- a/examples_ptx/mergeSort/Makefile_gpu
+++ b/examples_ptx/mergeSort/Makefile_gpu
@@ -2,7 +2,7 @@ PROG=mergeSort
 ISPC_SRC=mergeSort.ispc
 #CU_SRC=mergeSort.cu
 CXX_SRC=mergeSort.cpp  mergeSort.cpp
-PTXCC_REGMAX=32
+PTXCC_REGMAX=64
 #PTXCC_FLAGS= -Xptxas=-O3
 
 # LLVM_GPU=1
diff --git a/examples_ptx/mergeSort/mergeSort.ispc b/examples_ptx/mergeSort/mergeSort.ispc
index 8abdac1e..52065fe9 100644
--- a/examples_ptx/mergeSort/mergeSort.ispc
+++ b/examples_ptx/mergeSort/mergeSort.ispc
@@ -225,6 +225,8 @@ void generateSampleRanksKernel(
     uniform int totalProgramCount)
 {
   const int pos = taskIndex * programCount + programIndex;
+  cif (pos >= totalProgramCount)
+    return;
 
   const int           i = pos & ((stride / SAMPLE_STRIDE) - 1);
   const int segmentBase = (pos - i) * (2 * SAMPLE_STRIDE);
@@ -285,6 +287,8 @@ void mergeRanksAndIndicesKernel(
     uniform int totalProgramCount)
 {
   int pos = taskIndex * programCount + programIndex;
+  cif (pos >= totalProgramCount)
+    return;
 
   const int           i = pos & ((stride / SAMPLE_STRIDE) - 1);
   const int segmentBase = (pos - i) * (2 * SAMPLE_STRIDE);
@@ -477,8 +481,101 @@ void mergeElementaryIntervalsKernel(
 
 }
 
+task
+void mergeElementaryIntervalsKernel(
+    uniform int mergePairs,
+    uniform Key_t dstKey[],
+    uniform Val_t dstVal[],
+    uniform Key_t srcKey[],
+    uniform Val_t srcVal[],
+    uniform int limitsA[],
+    uniform int limitsB[],
+    uniform int stride,
+    uniform int N)
+{
+  const uniform int blockIdx = taskIndex;
+  const uniform int blockDim = (mergePairs + taskCount - 1)/taskCount;
+  const uniform int blockBeg =     blockIdx * blockDim;
+  const uniform int blockEnd = min(blockBeg + blockDim, mergePairs);
+
+  for (uniform int block = blockBeg; block < blockEnd; block++)
+  {
+    const int uniform   intervalI =  block & ((2 * stride) / SAMPLE_STRIDE - 1);
+    const int uniform segmentBase = (block - intervalI) * SAMPLE_STRIDE;
+
+    //Set up threadblock-wide parameters
+
+    const uniform int segmentElementsA = stride;
+    const uniform int segmentElementsB = min(stride, N - segmentBase - stride);
+    const uniform int  segmentSamplesA = getSampleCount(segmentElementsA);
+    const uniform int  segmentSamplesB = getSampleCount(segmentElementsB);
+    const uniform int   segmentSamples = segmentSamplesA + segmentSamplesB;
+
+    const uniform int startSrcA = limitsA[block];
+    const uniform int startSrcB = limitsB[block];
+    const uniform int endSrcA   = (intervalI + 1 < segmentSamples) ? limitsA[block + 1] : segmentElementsA;
+    const uniform int endSrcB   = (intervalI + 1 < segmentSamples) ? limitsB[block + 1] : segmentElementsB;
+    const uniform int lenSrcA   = endSrcA - startSrcA;
+    const uniform int lenSrcB   = endSrcB - startSrcB;
+    const uniform int startDstA = startSrcA + startSrcB;
+    const uniform int startDstB = startDstA + lenSrcA;
+
+    //Load main input data
+
+    Key_t keyA, keyB;
+    Val_t valA, valB;
+    if (programIndex < lenSrcA)
+    {
+      keyA = srcKey[segmentBase + startSrcA + programIndex];
+      valA = srcVal[segmentBase + startSrcA + programIndex];
+    }
+
+    if (programIndex < lenSrcB)
+    {
+      keyB = srcKey[segmentBase + stride + startSrcB + programIndex];
+      valB = srcVal[segmentBase + stride + startSrcB + programIndex];
+    }
+
+    // Compute destination addresses for merge data
+    int dstPosA, dstPosB;
+    if (programIndex < lenSrcA)
+      dstPosA = binarySearchExclusive1(keyA, keyB, lenSrcB, SAMPLE_STRIDE) + programIndex;
+    if (programIndex < lenSrcB)
+      dstPosB = binarySearchInclusive1(keyB, keyA, lenSrcA, SAMPLE_STRIDE) + programIndex;
+
+
+    int dstA = -1, dstB = -1;
+    if (programIndex < lenSrcA && dstPosA < lenSrcA)
+      dstA = segmentBase + startDstA + dstPosA;
+    if (programIndex < lenSrcB && dstPosB < lenSrcA)
+      dstB = segmentBase + startDstA + dstPosB;
+
+    dstPosA -= lenSrcA;
+    dstPosB -= lenSrcA;
+    if (programIndex < lenSrcA && dstPosA < lenSrcB)
+      dstA = segmentBase + startDstB + dstPosA;
+    if (programIndex < lenSrcB && dstPosB < lenSrcB)
+      dstB = segmentBase + startDstB + dstPosB;
+
+    // store merge data
+    if (dstA >= 0) 
+    {
+      dstKey[dstA] = keyA;
+      dstVal[dstA] = valA;
+    }
+    if (dstB >= 0) 
+    {
+      dstKey[dstB] = keyB;
+      dstVal[dstB] = valB;
+    }
+  }
+
+}
+
+
 static inline
 void mergeElementaryIntervals(
+    uniform int nTasks,
     uniform Key_t dstKey[],
     uniform Val_t dstVal[],
     uniform Key_t srcKey[],
@@ -492,6 +589,7 @@ void mergeElementaryIntervals(
   const uniform int mergePairs = (lastSegmentElements > stride) ? getSampleCount(N) : (N - lastSegmentElements) / SAMPLE_STRIDE;
 
 
+#if 0
   launch [mergePairs] mergeElementaryIntervalsKernel(
         dstKey,
         dstVal,
@@ -501,6 +599,18 @@ void mergeElementaryIntervals(
         limitsB,
         stride,
         N);
+#else
+  launch [nTasks] mergeElementaryIntervalsKernel(
+      mergePairs,
+      dstKey,
+      dstVal,
+      srcKey,
+      srcVal,
+      limitsA,
+      limitsB,
+      stride,
+      N);
+#endif
   sync;
 }
 
@@ -516,6 +626,9 @@ export
 void openMergeSort()
 {
   nTasks = num_cores()*4;
+#ifdef __NVPTX__
+  nTasks = num_cores()*13;
+#endif
   MAX_SAMPLE_COUNT = 8*32 * 131072 / programCount;
   assert(memPool == NULL);
   const uniform int nalloc = MAX_SAMPLE_COUNT * 4;
@@ -582,7 +695,7 @@ void mergeSort(
     mergeRanksAndIndices(limitsA, limitsB, ranksA, ranksB, stride, N);
         
     //Merge elementary intervals
-    mergeElementaryIntervals(oKey, oVal, iKey, iVal, limitsA, limitsB, stride, N);
+    mergeElementaryIntervals(nTasks, oKey, oVal, iKey, iVal, limitsA, limitsB, stride, N);
 
     if (lastSegmentElements <= stride)
       foreach (i = 0 ... lastSegmentElements)