supress warning of bang wildcard pattern-binding (i.e. let !_ = rhs). This fixes #9127

compiler/rename/RnBinds.lhs

@@ -476,8 +476,9 @@ rnBind _ bind@(PatBind { pat_lhs = pat
               bndrs = collectPatBinders pat
               bind' = bind { pat_rhs  = grhss', bind_fvs = fvs' }
               is_wild_pat = case pat of
-                              L _ (WildPat {}) -> True
-                              _                -> False
+                              L _ (WildPat {})                 -> True
+                              L _ (BangPat (L _ (WildPat {}))) -> True -- #9127
+                              _                                -> False
 
         -- Warn if the pattern binds no variables, except for the
         -- entirely-explicit idiom    _ = rhs

testsuite/tests/rename/should_compile/T9127.hs

+{-# LANGUAGE BangPatterns #-}
+module T9127 where
+
+f = let !_ = 2 * 2
+    in 2*2

testsuite/tests/rename/should_compile/all.T

@@ -214,3 +214,4 @@ test('T7969',
                    'T7969.imports'])],
      run_command,
      ['$MAKE -s --no-print-directory T7969'])
+test('T9127', normal, compile, [''])