[AMDGPU] Add convergent attribute to WWM.

Add the convergent attribute to the WWM intrinsic to stop it ever being
sunk out of cfg.

Differential Revision: https://reviews.llvm.org/D59536

llvm-svn: 356470

llvm/include/llvm/IR/IntrinsicsAMDGPU.td

@@ -1361,7 +1361,7 @@ def int_amdgcn_kill : Intrinsic<[], [llvm_i1_ty], []>;
 // enabled, with a few exceptions: - Phi nodes with require WWM return an
 // undefined value.
 def int_amdgcn_wwm : Intrinsic<[llvm_any_ty],
-  [LLVMMatchType<0>], [IntrNoMem, IntrSpeculatable]
+  [LLVMMatchType<0>], [IntrNoMem, IntrSpeculatable, IntrConvergent]
 >;
 
 // Given a value, copies it while setting all the inactive lanes to a given