[AMDGPU] Support horizontal vectorization of min/max.

Author: FarhanaAleen

Reviewed By: rampitec

Subscribers: AMDGPU

Differential Revision: https://reviews.llvm.org/D46604

llvm-svn: 331920
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp b/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
index d9bee12..3ea7a82 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
@@ -483,6 +483,22 @@
   return LT.first * getFullRateInstrCost();
 }
 
+int AMDGPUTTIImpl::getMinMaxReductionCost(Type *Ty, Type *CondTy,
+                                          bool IsPairwise,
+                                          bool IsUnsigned) {
+  EVT OrigTy = TLI->getValueType(DL, Ty);
+
+  // Computes cost on targets that have packed math instructions(which support
+  // 16-bit types only).
+  if (IsPairwise ||
+      !ST->hasVOP3PInsts() ||
+      OrigTy.getScalarSizeInBits() != 16)
+    return BaseT::getMinMaxReductionCost(Ty, CondTy, IsPairwise, IsUnsigned);
+
+  std::pair<int, MVT> LT = TLI->getTypeLegalizationCost(DL, Ty);
+  return LT.first * getHalfRateInstrCost();
+}
+
 int AMDGPUTTIImpl::getVectorInstrCost(unsigned Opcode, Type *ValTy,
                                       unsigned Index) {
   switch (Opcode) {