[AMDGPU] Calculate number of min/max SGPRs/VGPRs for WavesPerEU instead of using switch statement

Differential Revision: https://reviews.llvm.org/D29741

llvm-svn: 294627
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.cpp b/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.cpp
index 8dfd89a..a924f69 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUSubtarget.cpp
@@ -190,7 +190,7 @@
 std::pair<unsigned, unsigned> AMDGPUSubtarget::getWavesPerEU(
   const Function &F) const {
   // Default minimum/maximum number of waves per execution unit.
-  std::pair<unsigned, unsigned> Default(1, 0);
+  std::pair<unsigned, unsigned> Default(1, getMaxWavesPerEU());
 
   // Default/requested minimum/maximum flat work group sizes.
   std::pair<unsigned, unsigned> FlatWorkGroupSizes = getFlatWorkGroupSizes(F);