Use isWaveSizeKnown instead of gnarly hack.

Author: AlexVlx

llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp

@@ -1025,13 +1025,10 @@ GCNTTIImpl::instCombineIntrinsic(InstCombiner &IC, IntrinsicInst &II) const {
     break;
   }
   case Intrinsic::amdgcn_wavefrontsize: {
-    // TODO: this is a workaround for the pseudo-generic target one gets with no
-    // specified mcpu, which spoofs its wave size to 64; it should be removed.
-    if ((ST->getCPU().empty() || ST->getCPU().starts_with("generic")) &&
-        !ST->getFeatureString().contains("+wavefrontsize"))
-      break;
-    return IC.replaceInstUsesWith(
-        II, ConstantInt::get(II.getType(), ST->getWavefrontSize()));
+    if (ST->isWaveSizeKnown())
+      return IC.replaceInstUsesWith(
+          II, ConstantInt::get(II.getType(), ST->getWavefrontSize()));
+    break;
   }
   case Intrinsic::amdgcn_wqm_vote: {
     // wqm_vote is identity when the argument is constant.