[project @ 2000-09-07 16:31:45 by simonpj]

* The simplifier used to glom together all the top-level bindings into
  a single Rec every time it was invoked.  The reason for this is explained
  in SimplCore.lhs, but for at least one simple program it meant that the
  simplifier never got around to unravelling the recursive group into
  non-recursive pieces.  So I've put the glomming under explicit flag
  control with a -fglom-binds simplifier pass.   A side benefit is
  that because it happens less often, the (expensive) SCC algorithm
  runs less often.

diff --git a/ghc/compiler/main/CmdLineOpts.lhs b/ghc/compiler/main/CmdLineOpts.lhs
index 49f35e0..73bc069 100644 (file)
--- a/ghc/compiler/main/CmdLineOpts.lhs
+++ b/ghc/compiler/main/CmdLineOpts.lhs
@@ -222,6 +222,7 @@ data CoreToDo               -- These are diff core-to-core passes,
   | CoreDoSpecialising
   | CoreDoUSPInf
   | CoreDoCPResult 
+  | CoreDoGlomBinds
   | CoreCSE
 \end{code}
 
@@ -506,6 +507,7 @@ classifyOpts = sep argv [] [] -- accumulators...
          "-ffloat-outwards-full" -> CORE_TD(CoreDoFloatOutwards True)
          "-fliberate-case"  -> CORE_TD(CoreLiberateCase)
          "-fcse"            -> CORE_TD(CoreCSE)
+         "-fglom-binds"     -> CORE_TD(CoreDoGlomBinds)
          "-fprint-core"     -> CORE_TD(CoreDoPrintCore)
          "-fstatic-args"    -> CORE_TD(CoreDoStaticArgs)
          "-fstrictness"     -> CORE_TD(CoreDoStrictness)

diff --git a/ghc/compiler/simplCore/SimplCore.lhs b/ghc/compiler/simplCore/SimplCore.lhs
index ddca237..cdeabf9 100644 (file)
--- a/ghc/compiler/simplCore/SimplCore.lhs
+++ b/ghc/compiler/simplCore/SimplCore.lhs
@@ -125,15 +125,8 @@ doCorePass us binds lrb rb CoreDoWorkerWrapper      = _scc_ "WorkWrap"      noSt
 doCorePass us binds lrb rb CoreDoSpecialising       = _scc_ "Specialise"    noStats (specProgram us binds)
 doCorePass us binds lrb rb CoreDoCPResult          = _scc_ "CPResult"      noStats (cprAnalyse binds)
 doCorePass us binds lrb rb CoreDoPrintCore         = _scc_ "PrintCore"     noStats (printCore binds)
-doCorePass us binds lrb rb CoreDoUSPInf
-  = _scc_ "CoreUsageSPInf" 
-    if opt_UsageSPOn then
-      do
-         (binds1, rules1) <- doUsageSPInf us binds lrb
-         return (zeroSimplCount, binds1, rules1)
-    else
-      trace "WARNING: ignoring requested -fusagesp pass; requires -fusagesp-on" $
-      return (zeroSimplCount, binds, Nothing)
+doCorePass us binds lrb rb CoreDoGlomBinds         = noStats (glomBinds binds)
+doCorePass us binds lrb rb CoreDoUSPInf                    = _scc_ "CoreUsageSPInf" noStats (doUsageSPInf us binds lrb)
 
 printCore binds = do dumpIfSet True "Print Core"
                               (pprCoreBindings binds)
@@ -144,6 +137,7 @@ noStats thing = do { binds <- thing; return (zeroSimplCount, binds, Nothing) }
 \end{code}
 
 
+
 %************************************************************************
 %*                                                                     *
 \subsection{Dealing with rules}
@@ -202,6 +196,41 @@ simpl_arg e
     returnSmpl (etaReduceExpr e')
 \end{code}
 
+\begin{code}
+glomBinds :: [CoreBind] -> IO [CoreBind]
+-- Glom all binds together in one Rec, in case any
+-- transformations have introduced any new dependencies
+--
+-- NB: the global invariant is this:
+--     *** the top level bindings are never cloned, and are always unique ***
+--
+-- We sort them into dependency order, but applying transformation rules may
+-- make something at the top refer to something at the bottom:
+--     f = \x -> p (q x)
+--     h = \y -> 3
+--     
+--     RULE:  p (q x) = h x
+--
+-- Applying this rule makes f refer to h, 
+-- although it doesn't appear to in the source program.  
+-- This pass lets us control where it happens.
+--
+-- NOTICE that this cannot happen for rules whose head is a locally-defined
+-- function.  It only happens for rules whose head is an imported function
+-- (p in the example above).  So, for example, the rule had been
+--     RULE: f (p x) = h x
+-- then the rule for f would be attached to f itself (in its IdInfo) 
+-- by prepareLocalRuleBase and h would be regarded by the occurrency 
+-- analyser as free in f.
+
+glomBinds binds
+  = do { beginPass "GlomBinds" ;
+        let { recd_binds = [Rec (flattenBinds binds)] } ;
+        return recd_binds }
+       -- Not much point in printing the result... 
+       -- just consumes output bandwidth
+\end{code}
+
 %************************************************************************
 %*                                                                     *
 \subsection{The driver for the simplifier}
@@ -220,26 +249,7 @@ simplifyPgm (imported_rule_ids, rule_lhs_fvs)
   = do {
        beginPass "Simplify";
 
-       -- Glom all binds together in one Rec, in case any
-       -- transformations have introduced any new dependencies
-       --
-       -- NB: the global invariant is this:
-       --      *** the top level bindings are never cloned, and are always unique ***
-       --
-       -- We sort them into dependency order, but applying transformation rules may
-       -- make something at the top refer to something at the bottom:
-       --      f = \x -> p (q x)
-       --      h = \y -> 3
-       --      
-       --      RULE:  p (q x) = h x
-       --
-       -- Applying this rule makes f refer to h, although it doesn't appear to in the
-       -- source program.  Our solution is to do this occasional glom-together step,
-       -- just once per overall simplfication step.
-
-       let { recd_binds = [Rec (flattenBinds binds)] };
-
-       (termination_msg, it_count, counts_out, binds') <- iteration us 1 zeroSimplCount recd_binds;
+       (termination_msg, it_count, counts_out, binds') <- iteration us 1 zeroSimplCount binds;
 
        dumpIfSet (opt_D_verbose_core2core && opt_D_dump_simpl_stats)
                  "Simplifier statistics"

diff --git a/ghc/driver/Main.hs b/ghc/driver/Main.hs
index d26abf8..5f37182 100644 (file)
--- a/ghc/driver/Main.hs
+++ b/ghc/driver/Main.hs
@@ -1,6 +1,6 @@
 {-# OPTIONS -W -fno-warn-incomplete-patterns #-}
 -----------------------------------------------------------------------------
--- $Id: Main.hs,v 1.56 2000/09/05 10:18:28 simonmar Exp $
+-- $Id: Main.hs,v 1.57 2000/09/07 16:31:45 simonpj Exp $
 --
 -- GHC Driver program
 --
@@ -517,6 +517,7 @@ hsc_minusO_flags = do
        "-fstrictness",
        "-fcpr-analyse",
        "-fworker-wrapper",
+       "-fglom-binds",
 
        "-fsimplify",
          "[",