Profiler is inconsistent about biography for GHC's heap

My slightly modified rnBind has this clause (i is an Int):

rnBind sig_fn
       trim
       i
       (L loc (FunBind { fun_id = name, 
                         fun_infix = inf, 
                         fun_matches = matches,
                         -- no pattern FVs
                         bind_fvs = _
                       }))
       -- invariant: no free vars here when it's a FunBind
  = i `seq` setSrcSpan loc $
    do  { let plain_name = unLoc name

    ; (matches', fvs) <- bindSigTyVarsFV (sig_fn plain_name) $
                -- bindSigTyVars tests for Opt_ScopedTyVars
                 rnMatchGroup (FunRhs plain_name inf) matches

    ; checkPrecMatch inf plain_name matches'

    ; return
        (L loc (trace ("Using FunBind for " ++ show i)
                (FunBind { fun_id = name, 
                                  fun_infix = inf, 
                                  fun_matches = matches',
                     bind_fvs = trim fvs, 
                                  fun_co_fn = idHsWrapper, 
                                  fun_tick = Nothing })),
          [plain_name],
          fvs)
      }

If I comment out the trace and run

ghc --make J -fforce-recomp +RTS -p -hcrnBind -hyHsBindLR -hb

then I get notrace.png, all VOID. However, with the trace I get trace.png, LAG turning into DRAG. The two graphs are also a slightly different shape, which is curious.

Also attached is the core for with and without the tracing. I think the only interesting difference is

-      a30_ [ALWAYS Just L] :: NameSet.FreeVars
+      a30_ [ALWAYS Just L] :: HsBinds.HsBindLR Name.Name Name.Name
       [Str: DmdType]
-      a30_ = w1_ ww3_ } in
-    let {
-      a31_ :: HsBinds.HsWrapper
-      []
-      a31_ =
-        __scc {rnBind ghc-6.9.20080517:RnBinds !}
-        __scc {idHsWrapper ghc-6.9.20080517:HsBinds} HsBinds.WpHole } in
-    let {
-      a32_ :: HsBinds.HsWrapper
-      []
-      a32_ =
-        __scc {rnBind ghc-6.9.20080517:RnBinds !}
-        __scc {idHsWrapper ghc-6.9.20080517:HsBinds} HsBinds.WpHole } in
-    let {
-      a33_ :: HsBinds.HsBindLR Name.Name Name.Name
-      [Str: DmdType]
-      a33_ =
-        HsBinds.FunBind
-          @ Name.Name
-          @ Name.Name
-          name_
-          inf_
-          ww2_
-          a32_
-          a30_
-          (Data.Maybe.Nothing @ (GHC.Base.Int, [Name.Name])) } in
+      a30_ =
+        Debug.Trace.trace
+          @ (HsBinds.HsBindLR Name.Name Name.Name)
+          lvl45_
+          (HsBinds.FunBind
+             @ Name.Name
+             @ Name.Name
+             name_
+             inf_
+             ww2_
+             (__scc {rnBind ghc-6.9.20080517:RnBinds !}
+              __scc {idHsWrapper ghc-6.9.20080517:HsBinds} HsBinds.WpHole)
+             (w1_ ww3_)
+             (Data.Maybe.Nothing @ (GHC.Base.Int, [Name.Name]))) } in

Trac metadata

Trac field	Value
Version	6.9
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Profiling
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown