id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
6047	GHC retains unnecessary binding	simonmar	simonpj	"milan posted this example on #6042, I'm making a separate ticket for it.  He says:

----------

BTW, when I preparing for the advanced functional programming course, I found out that the following code

{{{
module Test where
factorial :: Int -> Int
factorial n | n > 0 = f n 1
  where f 0 acc = acc
        f n acc = f (n-1) (n * acc)
}}}

produces the following STG, on both GHC 7.0.4 and 7.4.1, with unused method `factorial_f`:

{{{
Test.factorial2 =
    \u srt:(0,*bitmap*) []
        Control.Exception.Base.patError
            ""a.hs:(4,1)-(6,35)|function factorial"";
SRT(Test.factorial2): [Control.Exception.Base.patError]
Test.$wf =
    \r [ww_srk ww1_sro]
        case ww_srk of wild_srm {
          __DEFAULT ->
              case *# [wild_srm ww1_sro] of sat_srK {
                __DEFAULT ->
                    case -# [wild_srm 1] of sat_srL {
                      __DEFAULT -> Test.$wf sat_srL sat_srK;
                    };
              };
          0 -> ww1_sro;
        };
SRT(Test.$wf): []
Test.factorial_f =
    \r [w_srs w1_srv]
        case w_srs of w2_srN {
          GHC.Types.I# ww_sry ->
              case w1_srv of w3_srM {
                GHC.Types.I# ww1_srz ->
                    case Test.$wf ww_sry ww1_srz of ww2_srB {
                      __DEFAULT -> GHC.Types.I# [ww2_srB];
                    };
              };
        };
SRT(Test.factorial_f): []
Test.factorial1 = NO_CCS GHC.Types.I#! [1];
SRT(Test.factorial1): []
Test.factorial =
    \r srt:(0,*bitmap*) [n_srD]
        case n_srD of wild_srP {
          GHC.Types.I# x_srG ->
              case ># [x_srG 0] of wild1_srO {
                GHC.Types.False -> Test.factorial2;
                GHC.Types.True ->
                    case Test.$wf x_srG 1 of ww_srJ {
                      __DEFAULT -> GHC.Types.I# [ww_srJ];
                    };
              };
        };
SRT(Test.factorial): [Test.factorial2]
}}}

The `Test.factorial_f` appears also in asm and in the object file.
----------

simonpj explained to me why this is happening: `factorial_f` is being retained because it is referenced in an INLINE pragma for `factorial`.  In fact it will never be used, because `factorial_f` itself is also INLINE.

We're going to investigate possible workarounds/solutions.

Note it's only a code size issue, performance is not affected (compile time is affected a little though).  We're not sure how much it happens.
"	bug	new	normal	7.6.2	Compiler	7.4.1				Unknown/Multiple	Unknown/Multiple	None/Unknown	Unknown