[AMDGPU] Add llvm.is.fpclass intrinsic to existing SelectionDAG fp
class support and introduce GlobalISel implementation for AMDGPU

Uses existing SelectionDAG lowering of the llvm.amdgcn.class intrinsic
for llvm.is.fpclass
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index b0bba68..7c27edd 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -4232,6 +4232,8 @@
   case G_ICMP:
   case G_FCMP:
     return fewerElementsVectorMultiEltType(GMI, NumElts, {1 /*cpm predicate*/});
+  case G_IS_FPCLASS:
+    return fewerElementsVectorMultiEltType(GMI, NumElts, {2, 3 /*mask,fpsem*/});
   case G_SELECT:
     if (MRI.getType(MI.getOperand(1).getReg()).isVector())
       return fewerElementsVectorMultiEltType(GMI, NumElts);