Turning off case liberation when using the hpc option, for now

Consider the following code

     f = g (case v of
              V a b -> a : t f)

where g is expensive. Liberate case will turn this into

     f = g (case v of
             V a b -> a : t (letrec f = g (case v of
                                           V a b -> a : f t)
                              in f)
           )

Yikes! We evaluate g twice. This leads to a O(2^n) explosion
if g calls back to the same code recursively.

This happen sometimes in HPC, because every tick is a liberate-able case,
but is a general problem to case liberation (I think).

diff --git a/compiler/main/DynFlags.hs b/compiler/main/DynFlags.hs
index c8615da..b3ee6fb 100644 (file)
--- a/compiler/main/DynFlags.hs
+++ b/compiler/main/DynFlags.hs
@@ -59,7 +59,7 @@ import PrelNames      ( mAIN )
 import StaticFlags     ( opt_Static )
 #endif
 import StaticFlags     ( opt_PIC, WayName(..), v_Ways, v_Build_tag,
-                         v_RTS_Build_tag )
+                         v_RTS_Build_tag, opt_Hpc )
 import {-# SOURCE #-} Packages (PackageState)
 import DriverPhases    ( Phase(..), phaseInputExt )
 import Config
@@ -677,6 +677,7 @@ getCoreToDo dflags
     cse           = dopt Opt_CSE dflags
     spec_constr   = dopt Opt_SpecConstr dflags
     liberate_case = dopt Opt_LiberateCase dflags
+                 && not opt_Hpc 
     rule_check    = ruleCheck dflags
 
     core_todo =