Make -frewrite-rules into a dynamic flag; off for -O0

Argubly rewrite rules should not fire with -O0, and it turns
out that when compiling GHC.Base with -O0 we get a crash if
the rewrite rules do fire (see Note [Scoping for Builtin rules]
in PrelRules).

So unless someone yells, rewrite rules are off with -O0.

The new (now dynamic) flag is
    -frewrite rules (with -fno-rewrite-rules to disable)

The old (static) flag -frules-off is gone.

diff --git a/compiler/deSugar/DsListComp.lhs b/compiler/deSugar/DsListComp.lhs
index 6a25a75..ccc1a7b 100644 (file)
--- a/compiler/deSugar/DsListComp.lhs
+++ b/compiler/deSugar/DsListComp.lhs
@@ -50,7 +50,7 @@ dsListComp lquals body elt_ty
     let
        quals = map unLoc lquals
     in
-    if opt_RulesOff || dopt Opt_IgnoreInterfacePragmas dflags
+    if not (dopt Opt_RewriteRules dflags) || dopt Opt_IgnoreInterfacePragmas dflags
        -- Either rules are switched off, or we are ignoring what there are;
        -- Either way foldr/build won't happen, so use the more efficient
        -- Wadler-style desugaring

diff --git a/compiler/main/DynFlags.hs b/compiler/main/DynFlags.hs
index 7022964..046e2b2 100644 (file)
--- a/compiler/main/DynFlags.hs
+++ b/compiler/main/DynFlags.hs
@@ -192,6 +192,7 @@ data DynFlag
    | Opt_CaseMerge
    | Opt_UnboxStrictFields
    | Opt_DictsCheap
+   | Opt_RewriteRules
 
    -- misc opts
    | Opt_Cpp
@@ -560,12 +561,16 @@ optLevelFlags :: [([Int], DynFlag)]
 optLevelFlags
   = [ ([0],    Opt_IgnoreInterfacePragmas)
     , ([0],     Opt_OmitInterfacePragmas)
+
     , ([1,2],  Opt_IgnoreAsserts)
+    , ([1,2],  Opt_RewriteRules)       -- Off for -O0; see Note [Scoping for Builtin rules]
+                                       --              in PrelRules
     , ([1,2],  Opt_DoEtaReduction)
     , ([1,2],  Opt_CaseMerge)
     , ([1,2],  Opt_Strictness)
     , ([1,2],  Opt_CSE)
     , ([1,2],  Opt_FullLaziness)
+
     , ([2],    Opt_LiberateCase)
     , ([2],    Opt_SpecConstr)
 
@@ -1067,7 +1072,8 @@ fFlags = [
   ( "asm-mangling",                    Opt_DoAsmMangling ),
   ( "print-bind-result",               Opt_PrintBindResult ),
   ( "force-recomp",                    Opt_ForceRecomp ),
-  ( "hpc-no-auto",                     Opt_Hpc_No_Auto )
+  ( "hpc-no-auto",                     Opt_Hpc_No_Auto ),
+  ( "rewrite-rules",                   Opt_RewriteRules )
   ]
 
 

diff --git a/compiler/main/StaticFlags.hs b/compiler/main/StaticFlags.hs
index fbdcb68..2a8c4dc 100644 (file)
--- a/compiler/main/StaticFlags.hs
+++ b/compiler/main/StaticFlags.hs
@@ -42,7 +42,6 @@ module StaticFlags (
        opt_NoMethodSharing, 
        opt_NoStateHack,
        opt_CprOff,
-       opt_RulesOff,
        opt_SimplNoPreInlining,
        opt_SimplExcessPrecision,
        opt_MaxWorkerArgs,
@@ -296,7 +295,6 @@ opt_Flatten                 = lookUp  FSLIT("-fflatten")
 opt_NoStateHack                        = lookUp  FSLIT("-fno-state-hack")
 opt_NoMethodSharing            = lookUp  FSLIT("-fno-method-sharing")
 opt_CprOff                     = lookUp  FSLIT("-fcpr-off")
-opt_RulesOff                   = lookUp  FSLIT("-frules-off")
        -- Switch off CPR analysis in the new demand analyser
 opt_MaxWorkerArgs              = lookup_def_int "-fmax-worker-args" (10::Int)
 
@@ -369,7 +367,6 @@ isStaticFlag f =
        "static",
        "funregisterised",
        "fext-core",
-       "frules-off",
        "fcpr-off",
        "ferror-spans",
        "fPIC"

diff --git a/compiler/prelude/PrelRules.lhs b/compiler/prelude/PrelRules.lhs
index 69901d3..165d008 100644 (file)
--- a/compiler/prelude/PrelRules.lhs
+++ b/compiler/prelude/PrelRules.lhs
@@ -44,9 +44,7 @@ import Name           ( Name, nameOccName )
 import Outputable
 import FastString
 import StaticFlags      ( opt_SimplExcessPrecision )
-
-import Data.Bits as Bits       ( Bits(..), shiftL, shiftR )
-       -- shiftL and shiftR were not always methods of Bits
+import Data.Bits as Bits
 import Data.Word       ( Word )
 \end{code}
 
@@ -447,6 +445,33 @@ dataToTagRule other = Nothing
 %*                                                                     *
 %************************************************************************
 
+Note [Scoping for Builtin rules]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+When compiling a (base-package) module that defines one of the
+functions mentioned in the RHS of a built-in rule, there's a danger
+that we'll see
+
+       f = ...(eq String x)....
+
+       ....and lower down...
+
+       eqString = ...
+
+Then a rewrite would give
+
+       f = ...(eqString x)...
+       ....and lower down...
+       eqString = ...
+
+and lo, eqString is not in scope.  This only really matters when we get to code
+generation.  With -O we do a GlomBinds step that does a new SCC analysis on the whole
+set of bindings, which sorts out the dependency.  Without -O we don't do any rule
+rewriting so again we are fine.
+
+(This whole thing doesn't show up for non-built-in rules because their dependencies
+are explicit.)
+
+
 \begin{code}
 builtinRules :: [CoreRule]
 -- Rules for non-primops that can't be expressed using a RULE pragma

diff --git a/compiler/simplCore/SimplUtils.lhs b/compiler/simplCore/SimplUtils.lhs
index 2e9c83d..3b304c6 100644 (file)
--- a/compiler/simplCore/SimplUtils.lhs
+++ b/compiler/simplCore/SimplUtils.lhs
@@ -774,10 +774,11 @@ activeInline env id
   where
     prag = idInlinePragma id
 
-activeRule :: SimplEnv -> Maybe (Activation -> Bool)
+activeRule :: DynFlags -> SimplEnv -> Maybe (Activation -> Bool)
 -- Nothing => No rules at all
-activeRule env
-  | opt_RulesOff = Nothing
+activeRule dflags env
+  | not (dopt Opt_RewriteRules dflags)
+  = Nothing    -- Rewriting is off
   | otherwise
   = case getMode env of
        SimplGently  -> Just isAlwaysActive

diff --git a/compiler/simplCore/Simplify.lhs b/compiler/simplCore/Simplify.lhs
index f27dcab..aab8925 100644 (file)
--- a/compiler/simplCore/Simplify.lhs
+++ b/compiler/simplCore/Simplify.lhs
@@ -967,7 +967,7 @@ completeCall env var cont
        -- So it's up to the programmer: rules can cause divergence
        ; let   in_scope   = getInScope env
                rules      = getRules env
-               maybe_rule = case activeRule env of
+               maybe_rule = case activeRule dflags env of
                                Nothing     -> Nothing  -- No rules apply
                                Just act_fn -> lookupRule act_fn in_scope 
                                                          rules var args 

diff --git a/docs/users_guide/flags.xml b/docs/users_guide/flags.xml
index 2f14127..b2c398d 100644 (file)
--- a/docs/users_guide/flags.xml
+++ b/docs/users_guide/flags.xml
@@ -928,7 +928,7 @@
          <tbody>
            <row>
              <entry><option>-fcase-merge</option></entry>
-             <entry>Enable case-merging</entry>
+             <entry>Enable case-merging. Implied by <option>-O</option>.</entry>
              <entry>dynamic</entry>
              <entry><option>-fno-case-merge</option></entry>
            </row>
@@ -942,7 +942,7 @@
 
            <row>
              <entry><option>-fdo-eta-reduction</option></entry>
-             <entry>Enable eta-reduction</entry>
+             <entry>Enable eta-reduction. Implied by <option>-O</option>.</entry>
              <entry>dynamic</entry>
              <entry><option>-fno-do-eta-reduction</option></entry>
            </row>
@@ -962,14 +962,6 @@
            </row>
 
            <row>
-             <entry><option>-frules-off</option></entry>
-             <entry>Switch off all rewrite rules (including rules
-             generated by automatic specialisation of overloaded functions)</entry>
-             <entry>static</entry>
-             <entry><option>-frules-off</option></entry>
-           </row>
-
-           <row>
              <entry><option>-fignore-asserts</option></entry>
              <entry>Ignore assertions in the source</entry>
              <entry>dynamic</entry>
@@ -984,13 +976,6 @@
            </row>
 
            <row>
-             <entry><option>-fliberate-case-threshold</option></entry>
-             <entry>Tweak the liberate-case optimisation (default: 10)</entry>
-             <entry>static</entry>
-             <entry><option>-fno-liberate-case-threshold</option></entry>
-           </row>
-
-           <row>
              <entry><option>-fomit-interface-pragmas</option></entry>
              <entry>Don't generate interface pragmas</entry>
              <entry>dynamic</entry>
@@ -1021,31 +1006,54 @@
            </row>
 
            <row>
-             <entry><option>-fno-cse</option></entry>
-             <entry>Turn off common sub-expression</entry>
+             <entry><option>-fcse</option></entry>
+             <entry>Turn on common sub-expression elimination. Implied by <option>-O</option>.</entry>
              <entry>dynamic</entry>
-             <entry>-</entry>
+             <entry>-fno-cse</entry>
            </row>
 
            <row>
-             <entry><option>-fno-full-laziness</option></entry>
-             <entry>Turn off full laziness (floating bindings outwards).</entry>
+             <entry><option>-ffull-laziness</option></entry>
+             <entry>Turn on full laziness (floating bindings outwards). Implied by <option>-O</option>.</entry>
              <entry>dynamic</entry>
-             <entry>-ffull-laziness</entry>
+             <entry>-fno-full-laziness</entry>
            </row>
 
            <row>
-             <entry><option>-fno-pre-inlining</option></entry>
-             <entry>Turn off pre-inlining</entry>
-             <entry>static</entry>
-             <entry>-</entry>
+             <entry><option>-frewrite-rules</option></entry>
+             <entry>Switch on all rewrite rules (including rules
+             generated by automatic specialisation of overloaded functions).
+             Implied by <option>-O</option>. </entry>
+             <entry>dynamic</entry>
+             <entry><option>-fno-rewrite-rules</option></entry>
            </row>
 
            <row>
-             <entry><option>-fno-strictness</option></entry>
-             <entry>Turn off strictness analysis</entry>
+             <entry><option>-fstrictness</option></entry>
+             <entry>Turn on strictness analysis. Implied by <option>-O</option>.</entry>
              <entry>dynamic</entry>
-             <entry>-</entry>
+             <entry>-fno-strictness</entry>
+           </row>
+
+           <row>
+             <entry><option>-fspec-constr</option></entry>
+             <entry>Turn on the SpecConstr transformation. Implied by <option>-O2</option>.</entry>
+             <entry>dynamic</entry>
+             <entry>-fno-spec-constr</entry>
+           </row>
+
+           <row>
+             <entry><option>-fliberate-case</option></entry>
+             <entry>Turn on the liberate-case transformation. Implied by <option>-O2</option>.</entry>
+             <entry>dynamic</entry>
+             <entry>-fno-liberate-case</entry>
+           </row>
+
+           <row>
+             <entry><option>-fliberate-case-threshold</option></entry>
+             <entry>Tweak the liberate-case optimisation (default: 10)</entry>
+             <entry>static</entry>
+             <entry><option>-fno-liberate-case-threshold</option></entry>
            </row>
 
            <row>
@@ -1089,6 +1097,13 @@
              <entry>static</entry>
              <entry><option>-fno-unfolding-use-threshold</option></entry>
            </row>
+
+           <row>
+             <entry><option>-fno-pre-inlining</option></entry>
+             <entry>Turn off pre-inlining</entry>
+             <entry>static</entry>
+             <entry>-</entry>
+           </row>
          </tbody>
        </tgroup>
       </informaltable>