Prevent excessive inlining with DPH

This adds a new flag -finline-if-enough-args which disables inlining for
partially applied functions. It is automatically set by -Odph. This is a
temporary hack and should remain undocumented.

MERGE TO 6.10

compiler/coreSyn/CoreUnfold.lhs

@@ -586,10 +586,13 @@ callSiteInline dflags active_inline id lone_variable arg_infos cont_info
 		  -> True
 
 	  	  | otherwise
-		  -> some_benefit && small_enough
+		  -> some_benefit && small_enough && inline_enough_args
 
 		  where
 		    enough_args	= n_val_args >= n_vals_wanted
+                    inline_enough_args =
+                      not (dopt Opt_InlineIfEnoughArgs dflags) || enough_args
+
 
 		    some_benefit = or arg_infos || really_interesting_cont
 				-- There must be something interesting

compiler/main/DynFlags.hs

@@ -261,6 +261,7 @@ data DynFlag
    | Opt_UnboxStrictFields
    | Opt_MethodSharing
    | Opt_DictsCheap
+   | Opt_InlineIfEnoughArgs
    | Opt_EnableRewriteRules		-- Apply rewrite rules during simplification
    | Opt_Vectorise
    | Opt_RegsGraph                      -- do graph coloring register allocation
@@ -1545,6 +1546,7 @@ fFlags = [
   ( "unbox-strict-fields",              Opt_UnboxStrictFields, const Supported ),
   ( "method-sharing",                   Opt_MethodSharing, const Supported ),
   ( "dicts-cheap",                      Opt_DictsCheap, const Supported ),
+  ( "inline-if-enough-args",            Opt_InlineIfEnoughArgs, const Supported ),
   ( "excess-precision",                 Opt_ExcessPrecision, const Supported ),
   ( "asm-mangling",                     Opt_DoAsmMangling, const Supported ),
   ( "print-bind-result",                Opt_PrintBindResult, const Supported ),
@@ -1908,6 +1910,7 @@ setOptLevel n dflags
 --    -fmax-simplifier-iterations20     this is necessary sometimes
 --    -fno-spec-constr-threshold        run SpecConstr even for big loops
 --    -fno-spec-constr-count            SpecConstr as much as possible
+--    -finline-enough-args              hack to prevent excessive inlining
 --
 setDPHOpt :: DynFlags -> DynFlags
 setDPHOpt dflags = setOptLevel 2 (dflags { maxSimplIterations  = 20
@@ -1916,6 +1919,7 @@ setDPHOpt dflags = setOptLevel 2 (dflags { maxSimplIterations  = 20
                                          })
                    `dopt_set`   Opt_DictsCheap
                    `dopt_unset` Opt_MethodSharing
+                   `dopt_set`   Opt_InlineIfEnoughArgs
 
 data DPHBackend = DPHPar
                 | DPHSeq