R600/SI: Add subtarget feature to enable VGPR spilling for all shader types

This is disabled by default, but can be enabled with the subtarget
feature: 'vgpr-spilling'

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226597 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/R600/SIISelLowering.cpp

@@ -588,6 +588,12 @@ SDValue SITargetLowering::LowerFormalArguments(
 
     InVals.push_back(Val);
   }
+
+  if (Info->getShaderType() != ShaderType::COMPUTE) {
+    unsigned ScratchIdx = CCInfo.getFirstUnallocated(
+        AMDGPU::SGPR_32RegClass.begin(), AMDGPU::SGPR_32RegClass.getNumRegs());
+    Info->ScratchOffsetReg = AMDGPU::SGPR_32RegClass.getRegister(ScratchIdx);
+  }
   return Chain;
 }