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.
ghc · May 4, 2007 · 5943ce9 · 5943ce9
1 parent 6f1d589
commit 5943ce9
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Showing 7 changed files with 86 additions and 42 deletions.
diff --git 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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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>
@@ -961,14 +961,6 @@
 	      <entry><option>-fno-excess-precision</option></entry>
 	    </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>
@@ -983,13 +975,6 @@
 	      <entry><option>-fno-ignore-interface-pragmas</option></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>
 	      <entry><option>-fomit-interface-pragmas</option></entry>
 	      <entry>Don't generate interface pragmas</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>