Comparison primops return Int# (Fixes #6135)

This patch modifies all comparison primops for Char#, Int#, Word#, Double#,
Float# and Addr# to return Int# instead of Bool. A value of 1# represents True
and 0# represents False. For a more detailed description of motivation for this
change, discussion of implementation details and benchmarking results please
visit the wiki page: http://hackage.haskell.org/trac/ghc/wiki/PrimBool

There's also some cleanup: whitespace fixes in files that were extensively edited
in this patch and constant folding rules for Integer div and mod operators (which
for some reason have been left out up till now).

2 files changed, 18 insertions, 23 deletions

diff --git a/compiler/codeGen/StgCmmExpr.hs b/compiler/codeGen/StgCmmExpr.hs
index 3d60def450..20b65ba4c7 100644
--- a/compiler/codeGen/StgCmmExpr.hs
+++ b/compiler/codeGen/StgCmmExpr.hs
@@ -141,9 +141,9 @@ cgLetNoEscapeRhsBody local_cc bndr (StgRhsClosure cc _bi _ _upd _ args body)
   = cgLetNoEscapeClosure bndr local_cc cc (nonVoidIds args) body
 cgLetNoEscapeRhsBody local_cc bndr (StgRhsCon cc con args)
   = cgLetNoEscapeClosure bndr local_cc cc [] (StgConApp con args)
-        -- For a constructor RHS we want to generate a single chunk of 
-        -- code which can be jumped to from many places, which will 
-        -- return the constructor. It's easy; just behave as if it 
+        -- For a constructor RHS we want to generate a single chunk of
+        -- code which can be jumped to from many places, which will
+        -- return the constructor. It's easy; just behave as if it
         -- was an StgRhsClosure with a ConApp inside!
 
 -------------------------
@@ -193,9 +193,9 @@ heapcheck will take their worst case into account.
 In favour of omitting !Q!, !R!:
 
  - *May* save a heap overflow test,
-   if ...P... allocates anything.  
+   if ...P... allocates anything.
 
- - We can use relative addressing from a single Hp to 
+ - We can use relative addressing from a single Hp to
    get at all the closures so allocated.
 
  - No need to save volatile vars etc across heap checks
@@ -203,7 +203,7 @@ In favour of omitting !Q!, !R!:
 
 Against omitting !Q!, !R!
 
-  - May put a heap-check into the inner loop.  Suppose 
+  - May put a heap-check into the inner loop.  Suppose
         the main loop is P -> R -> P -> R...
         Q is the loop exit, and only it does allocation.
     This only hurts us if P does no allocation.  If P allocates,
@@ -212,7 +212,7 @@ Against omitting !Q!, !R!
   - May do more allocation than reqd.  This sometimes bites us
     badly.  For example, nfib (ha!) allocates about 30\% more space if the
     worst-casing is done, because many many calls to nfib are leaf calls
-    which don't need to allocate anything. 
+    which don't need to allocate anything.
 
     We can un-allocate, but that costs an instruction
 
@@ -248,7 +248,7 @@ Hence: two basic plans for
 
         ...save current cost centre...
 
-        ...code for e, 
+        ...code for e,
            with sequel (SetLocals r)
 
         ...restore current cost centre...
@@ -338,8 +338,12 @@ So we add a special case to generate
 
 and later optimisations will further improve this.
 
-We should really change all these primops to return Int# instead, that
-would make this special case go away.
+Now that #6135 has been resolved it should be possible to remove that
+special case. The idea behind this special case and pre-6135 implementation
+of Bool-returning primops was that tagToEnum# was added implicitly in the
+codegen and then optimized away. Now the call to tagToEnum# is explicit
+in the source code, which allows to optimize it away at the earlier stages
+of compilation (i.e. at the Core level).
 -}
 
 
@@ -498,7 +502,7 @@ cgAlts gc_plan bndr (PrimAlt _) alts
                 -- PrimAlts always have a DEFAULT case
                 -- and it always comes first
 
-              tagged_cmms' = [(lit,code) 
+              tagged_cmms' = [(lit,code)
                              | (LitAlt lit, code) <- tagged_cmms]
         ; emitCmmLitSwitch (CmmReg bndr_reg) tagged_cmms' deflt
         ; return AssignedDirectly }
@@ -637,7 +641,7 @@ cgLneJump blk_id lne_regs args  -- Join point; discard sequel
         ; emitMultiAssign lne_regs cmm_args
         ; emit (mkBranch blk_id)
         ; return AssignedDirectly }
-    
+
 cgTailCall :: Id -> CgIdInfo -> [StgArg] -> FCode ReturnKind
 cgTailCall fun_id fun_info args = do
     dflags <- getDynFlags
@@ -645,7 +649,7 @@ cgTailCall fun_id fun_info args = do
 
             -- A value in WHNF, so we can just return it.
         ReturnIt -> emitReturn [fun]    -- ToDo: does ReturnIt guarantee tagged?
-    
+
         EnterIt -> ASSERT( null args )  -- Discarding arguments
                    emitEnter fun
 
@@ -653,7 +657,7 @@ cgTailCall fun_id fun_info args = do
                 { tickySlowCall lf_info args
                 ; emitComment $ mkFastString "slowCall"
                 ; slowCall fun args }
-    
+
         -- A direct function call (possibly with some left-over arguments)
         DirectEntry lbl arity -> do
                 { tickyDirectCall arity args
diff --git a/compiler/codeGen/StgCmmPrim.hs b/compiler/codeGen/StgCmmPrim.hs
index 7ce329a707..2c044faa42 100644
--- a/compiler/codeGen/StgCmmPrim.hs
+++ b/compiler/codeGen/StgCmmPrim.hs
@@ -107,15 +107,6 @@ cgOpApp (StgPrimOp primop) args res_ty
        cgPrimOp regs primop args
        emitReturn (map (CmmReg . CmmLocal) regs)
 
-  | ReturnsAlg tycon <- result_info
-  , isEnumerationTyCon tycon
-        -- c.f. cgExpr (...TagToEnumOp...)
-  = do dflags <- getDynFlags
-       tag_reg <- newTemp (bWord dflags)
-       cgPrimOp [tag_reg] primop args
-       emitReturn [tagToClosure dflags tycon
-                                (CmmReg (CmmLocal tag_reg))]
-
   | otherwise = panic "cgPrimop"
   where
      result_info = getPrimOpResultInfo primop