Wibbles to the inline-in-InlineRule stuff

[ghc-hetmet.git] / compiler / simplCore / SimplUtils.lhs

diff --git a/compiler/simplCore/SimplUtils.lhs b/compiler/simplCore/SimplUtils.lhs
index 1511a2f..c87e1fc 100644 (file)
--- a/compiler/simplCore/SimplUtils.lhs
+++ b/compiler/simplCore/SimplUtils.lhs
@@ -11,7 +11,7 @@ module SimplUtils (
        -- Inlining,
        preInlineUnconditionally, postInlineUnconditionally, 
        activeInline, activeRule, 
-        simplEnvForGHCi, simplEnvForRules, simplGentlyForInlineRules,
+        simplEnvForGHCi, simplEnvForRules, updModeForInlineRules,
 
        -- The continuation type
        SimplCont(..), DupFlag(..), ArgInfo(..),
@@ -422,8 +422,11 @@ simplEnvForRules :: SimplEnv
 simplEnvForRules = mkSimplEnv allOffSwitchChecker $
                    SimplGently { sm_rules = True, sm_inline = False }
 
-simplGentlyForInlineRules :: SimplifierMode
-simplGentlyForInlineRules = SimplGently { sm_rules = True, sm_inline = True }
+updModeForInlineRules :: SimplifierMode -> SimplifierMode
+updModeForInlineRules mode
+  = case mode of      
+      SimplGently {} -> mode   -- Don't modify mode if we already gentle
+      SimplPhase  {} -> SimplGently { sm_rules = True, sm_inline = True }
        -- Simplify as much as possible, subject to the usual "gentle" rules
 \end{code}
 
@@ -476,6 +479,19 @@ running it, we don't want to use -O2.  Indeed, we don't want to inline
 anything, because the byte-code interpreter might get confused about 
 unboxed tuples and suchlike.
 
+Note [RULEs enabled in SimplGently]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+RULES are enabled when doing "gentle" simplification.  Two reasons:
+
+  * We really want the class-op cancellation to happen:
+        op (df d1 d2) --> $cop3 d1 d2
+    because this breaks the mutual recursion between 'op' and 'df'
+
+  * I wanted the RULE
+        lift String ===> ...
+    to work in Template Haskell when simplifying
+    splices, so we get simpler code for literal strings
+
 Note [Simplifying gently inside InlineRules]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 We don't do much simplification inside InlineRules (which come from
@@ -805,13 +821,8 @@ activeRule dflags env
   | otherwise
   = case getMode env of
       SimplGently { sm_rules = rules_on } 
-        | rules_on  -> Just isEarlyActive
+        | rules_on  -> Just isEarlyActive      -- Note [RULEs enabled in SimplGently]
         | otherwise -> Nothing
-                       -- Used to be Nothing (no rules in gentle mode)
-                       -- Main motivation for changing is that I wanted
-                       --      lift String ===> ...
-                       -- to work in Template Haskell when simplifying
-                       -- splices, so we get simpler code for literal strings
       SimplPhase n _ -> Just (isActive n)
 \end{code}