Fix an SRT-related bug

We were using the SRT information generated by the computeSRTs pass to
decide whether to add a static link field to a constructor or not, and
this broke when I disabled computeSRTs for the new code generator.  So
I've hacked it for now to only rely on the SRT information generated
by CoreToStg.

compiler/codeGen/StgCmmBind.hs

@@ -76,16 +76,16 @@ cgTopRhsClosure :: Id
 cgTopRhsClosure id ccs _ upd_flag srt args body = do
   {	-- LAY OUT THE OBJECT
     let name = idName id
-  ; lf_info  <- mkClosureLFInfo id TopLevel [] upd_flag args
-  ; srt_info <- getSRTInfo srt
+  ; lf_info <- mkClosureLFInfo id TopLevel [] upd_flag args
+  ; has_srt <- getSRTInfo srt
   ; mod_name <- getModuleName
   ; let descr         = closureDescription mod_name name
-	closure_info  = mkClosureInfo True id lf_info 0 0 srt_info descr
+        closure_info  = mkClosureInfo True id lf_info 0 0 descr
 	closure_label = mkLocalClosureLabel name (idCafInfo id)
     	cg_id_info    = litIdInfo id lf_info (CmmLabel closure_label)
         caffy         = idCafInfo id
         info_tbl      = mkCmmInfo closure_info -- XXX short-cut
-        closure_rep   = mkStaticClosureFields info_tbl ccs caffy []
+        closure_rep   = mkStaticClosureFields info_tbl ccs caffy has_srt []
 
   	 -- BUILD THE OBJECT, AND GENERATE INFO TABLE (IF NECESSARY)
   ; emitDataLits closure_label closure_rep
@@ -161,8 +161,8 @@ cgRhs :: Id -> StgRhs -> FCode (CgIdInfo, CmmAGraph)
 cgRhs name (StgRhsCon cc con args)
   = buildDynCon name cc con args
 
-cgRhs name (StgRhsClosure cc bi fvs upd_flag srt args body)
-  = mkRhsClosure name cc bi (nonVoidIds fvs) upd_flag srt args body
+cgRhs name (StgRhsClosure cc bi fvs upd_flag _srt args body)
+  = mkRhsClosure name cc bi (nonVoidIds fvs) upd_flag args body
 
 ------------------------------------------------------------------------
 --		Non-constructor right hand sides
@@ -170,7 +170,7 @@ cgRhs name (StgRhsClosure cc bi fvs upd_flag srt args body)
 
 mkRhsClosure :: Id -> CostCentreStack -> StgBinderInfo
 	     -> [NonVoid Id]			-- Free vars
-	     -> UpdateFlag -> SRT
+             -> UpdateFlag
 	     -> [Id]			        -- Args
 	     -> StgExpr
 	     -> FCode (CgIdInfo, CmmAGraph)
@@ -214,8 +214,7 @@ for semi-obvious reasons.
 mkRhsClosure	bndr cc bi
 		[NonVoid the_fv]   		-- Just one free var
 		upd_flag		-- Updatable thunk
-		_srt
-		[]			-- A thunk
+                []                      -- A thunk
 		body@(StgCase (StgApp scrutinee [{-no args-}])
 		      _ _ _ _   -- ignore uniq, etc.
 		      (AlgAlt _)
@@ -246,8 +245,7 @@ mkRhsClosure	bndr cc bi
 mkRhsClosure    bndr cc bi
 		fvs
 		upd_flag
-		_srt
-		[]			-- No args; a thunk
+                []                      -- No args; a thunk
 		body@(StgApp fun_id args)
 
   | args `lengthIs` (arity-1)
@@ -268,7 +266,7 @@ mkRhsClosure    bndr cc bi
 	arity 	= length fvs
 
 ---------- Default case ------------------
-mkRhsClosure bndr cc _ fvs upd_flag srt args body
+mkRhsClosure bndr cc _ fvs upd_flag args body
   = do	{ 	-- LAY OUT THE OBJECT
 	-- If the binder is itself a free variable, then don't store
 	-- it in the closure.  Instead, just bind it to Node on entry.
@@ -287,8 +285,7 @@ mkRhsClosure bndr cc _ fvs upd_flag srt args body
 	-- MAKE CLOSURE INFO FOR THIS CLOSURE
 	; lf_info <- mkClosureLFInfo bndr NotTopLevel fvs upd_flag args
 	; mod_name <- getModuleName
-	; c_srt <- getSRTInfo srt
-	; let	name  = idName bndr
+        ; let   name  = idName bndr
 		descr = closureDescription mod_name name
 		fv_details :: [(NonVoid Id, VirtualHpOffset)]
 		(tot_wds, ptr_wds, fv_details)
@@ -296,7 +293,7 @@ mkRhsClosure bndr cc _ fvs upd_flag srt args body
 				       (addIdReps (map stripNV reduced_fvs))
 		closure_info = mkClosureInfo False	-- Not static
 					     bndr lf_info tot_wds ptr_wds
-					     c_srt descr
+                                             descr
 
 	-- BUILD ITS INFO TABLE AND CODE
 	; forkClosureBody $
@@ -342,8 +339,7 @@ cgStdThunk bndr _cc _bndr_info _body lf_info payload
 	descr = closureDescription mod_name (idName bndr)
 	closure_info = mkClosureInfo False 	-- Not static
 				     bndr lf_info tot_wds ptr_wds
-				     NoC_SRT	-- No SRT for a std-form closure
-				     descr
+                                     descr
 
 --  ; (use_cc, blame_cc) <- chooseDynCostCentres cc [{- no args-}] body
   ; let use_cc = curCCS; blame_cc = curCCS

compiler/codeGen/StgCmmClosure.hs

@@ -650,7 +650,6 @@ data ClosureInfo
           -- the rest is just an unpacked CmmInfoTable.
         closureInfoLabel :: !CLabel,
         closureSMRep     :: !SMRep,          -- representation used by storage mgr
-        closureSRT       :: !C_SRT,          -- What SRT applies to this closure
         closureProf      :: !ProfilingInfo
     }
 
@@ -660,7 +659,7 @@ mkCmmInfo ClosureInfo {..}
   = CmmInfoTable { cit_lbl  = closureInfoLabel
                  , cit_rep  = closureSMRep
                  , cit_prof = closureProf
-                 , cit_srt  = closureSRT }
+                 , cit_srt  = NoC_SRT }
 
 
 --------------------------------------
@@ -671,16 +670,14 @@ mkClosureInfo :: Bool		-- Is static
 	      -> Id
 	      -> LambdaFormInfo 
 	      -> Int -> Int	-- Total and pointer words
-	      -> C_SRT
-	      -> String		-- String descriptor
+              -> String         -- String descriptor
 	      -> ClosureInfo
-mkClosureInfo is_static id lf_info tot_wds ptr_wds srt_info val_descr
+mkClosureInfo is_static id lf_info tot_wds ptr_wds val_descr
   = ClosureInfo { closureName      = name,
                   closureLFInfo    = lf_info,
-                  closureInfoLabel = info_lbl,
-                  closureSMRep     = sm_rep,    -- These four fields are a
-                  closureSRT       = srt_info,  --        CmmInfoTable
-                  closureProf      = prof }     -- ---
+                  closureInfoLabel = info_lbl,  -- These three fields are
+                  closureSMRep     = sm_rep,    -- (almost) an info table
+                  closureProf      = prof }     -- (we don't have an SRT yet)
   where
     name       = idName id
     sm_rep     = mkHeapRep is_static ptr_wds nonptr_wds (lfClosureType lf_info)
@@ -906,15 +903,21 @@ cafBlackHoleInfoTable
                  , cit_prof = NoProfilingInfo
                  , cit_srt  = NoC_SRT }
 
-staticClosureNeedsLink :: CmmInfoTable -> Bool
+staticClosureNeedsLink :: Bool -> CmmInfoTable -> Bool
 -- A static closure needs a link field to aid the GC when traversing
 -- the static closure graph.  But it only needs such a field if either
 -- 	a) it has an SRT
 --	b) it's a constructor with one or more pointer fields
 -- In case (b), the constructor's fields themselves play the role
 -- of the SRT.
-staticClosureNeedsLink info_tbl@CmmInfoTable{ cit_rep = smrep }
+--
+-- At this point, the cit_srt field has not been calculated (that
+-- happens right at the end of the Cmm pipeline), but we do have the
+-- VarSet of CAFs that CoreToStg attached, and if that is empty there
+-- will definitely not be an SRT.
+--
+staticClosureNeedsLink has_srt CmmInfoTable{ cit_rep = smrep }
   | isConRep smrep         = not (isStaticNoCafCon smrep)
-  | otherwise              = needsSRT (cit_srt info_tbl)
-staticClosureNeedsLink _ = False
+  | otherwise              = has_srt -- needsSRT (cit_srt info_tbl)
+staticClosureNeedsLink _ _ = False
 

compiler/codeGen/StgCmmCon.hs

@@ -92,6 +92,7 @@ cgTopRhsCon id con args
                              info_tbl
                              dontCareCCS                -- Because it's static data
                              caffy                      -- Has CAF refs
+                             False                      -- no SRT
                              payload
 
                 -- BUILD THE OBJECT

compiler/codeGen/StgCmmForeign.hs

@@ -72,10 +72,7 @@ cgForeignCall results result_hints (CCall (CCallSpec target cconv safety)) stg_a
               fc = ForeignConvention cconv arg_hints result_hints
               call_target = ForeignTarget cmm_target fc
 
-        ; srt <- getSRTInfo NoSRT        -- SLPJ: Not sure what SRT
-                                        -- is right here
-                                        -- JD: Does it matter in the new codegen?
-        ; emitForeignCall safety results call_target call_args srt CmmMayReturn }
+        ; emitForeignCall safety results call_target call_args CmmMayReturn }
   where
         -- in the stdcall calling convention, the symbol needs @size appended
         -- to it, where size is the total number of bytes of arguments.  We
@@ -93,9 +90,7 @@ emitCCall :: [(CmmFormal,ForeignHint)]
           -> [(CmmActual,ForeignHint)]
           -> FCode ()
 emitCCall hinted_results fn hinted_args
-  = emitForeignCall PlayRisky results target args
-                    NoC_SRT -- No SRT b/c we PlayRisky
-                    CmmMayReturn
+  = emitForeignCall PlayRisky results target args CmmMayReturn
   where
     (args, arg_hints) = unzip hinted_args
     (results, result_hints) = unzip hinted_results
@@ -105,7 +100,7 @@ emitCCall hinted_results fn hinted_args
 
 emitPrimCall :: [CmmFormal] -> CallishMachOp -> [CmmActual] -> FCode ()
 emitPrimCall res op args
-  = emitForeignCall PlayRisky res (PrimTarget op) args NoC_SRT CmmMayReturn
+  = emitForeignCall PlayRisky res (PrimTarget op) args CmmMayReturn
 
 -- alternative entry point, used by CmmParse
 emitForeignCall
@@ -113,11 +108,10 @@ emitForeignCall
         -> [CmmFormal]          -- where to put the results
         -> ForeignTarget        -- the op
         -> [CmmActual]          -- arguments
-        -> C_SRT                -- the SRT of the calls continuation
         -> CmmReturnInfo        -- This can say "never returns"
                                 --   only RTS procedures do this
         -> FCode ()
-emitForeignCall safety results target args _srt _ret
+emitForeignCall safety results target args _ret
   | not (playSafe safety) = do
     let (caller_save, caller_load) = callerSaveVolatileRegs
     emit caller_save

compiler/codeGen/StgCmmHeap.hs

@@ -151,9 +151,10 @@ mkStaticClosureFields
         :: CmmInfoTable
         -> CostCentreStack
         -> CafInfo
+        -> Bool                 -- SRT is non-empty?
         -> [CmmLit]             -- Payload
         -> [CmmLit]             -- The full closure
-mkStaticClosureFields info_tbl ccs caf_refs payload
+mkStaticClosureFields info_tbl ccs caf_refs has_srt payload
   = mkStaticClosure info_lbl ccs payload padding
         static_link_field saved_info_field
   where
@@ -178,8 +179,10 @@ mkStaticClosureFields info_tbl ccs caf_refs payload
         | otherwise  = ASSERT(null payload) [mkIntCLit 0]
 
     static_link_field
-        | is_caf || staticClosureNeedsLink info_tbl = [static_link_value]
-        | otherwise                                 = []
+        | is_caf || staticClosureNeedsLink has_srt info_tbl
+        = [static_link_value]
+        | otherwise
+        = []
 
     saved_info_field
         | is_caf     = [mkIntCLit 0]

compiler/codeGen/StgCmmUtils.hs

@@ -71,6 +71,7 @@ import Module
 import Literal
 import Digraph
 import ListSetOps
+import VarSet
 import Util
 import Unique
 import DynFlags
@@ -811,36 +812,13 @@ assignTemp' e
 --
 -------------------------------------------------------------------------
 
--- There is just one SRT for each top level binding; all the nested
--- bindings use sub-sections of this SRT.  The label is passed down to
--- the nested bindings via the monad.
-
-getSRTInfo :: SRT -> FCode C_SRT
-getSRTInfo (SRTEntries {}) = return NoC_SRT --panic "getSRTInfo"
-
-getSRTInfo (SRT off len bmp)
-  | len > hALF_WORD_SIZE_IN_BITS || bmp == [fromIntegral srt_escape]
-  = do 	{ id <- newUnique
-	-- ; top_srt <- getSRTLabel
-        ; let srt_desc_lbl = mkLargeSRTLabel id
-        -- JD: We're not constructing and emitting SRTs in the back end,
-        -- which renders this code wrong (it now names a now-non-existent label).
-	-- ; emitRODataLits srt_desc_lbl
-        --      ( cmmLabelOffW top_srt off
-	--        : mkWordCLit (fromIntegral len)
-	--        : map mkWordCLit bmp)
-	; return (C_SRT srt_desc_lbl 0 srt_escape) }
-
-  | otherwise
-  = do	{ top_srt <- getSRTLabel
-	; return (C_SRT top_srt off (fromIntegral (head bmp))) }
-	-- The fromIntegral converts to StgHalfWord
-
-getSRTInfo NoSRT 
-  = -- TODO: Should we panic in this case?
-    -- Someone obviously thinks there should be an SRT
-    return NoC_SRT
-
+-- | Returns 'True' if there is a non-empty SRT, or 'False' otherwise
+-- NB. the SRT attached to an StgBind is still used in the new codegen
+-- to decide whether we need a static link field on a static closure
+-- or not.
+getSRTInfo :: SRT -> FCode Bool
+getSRTInfo (SRTEntries vs) = return (not (isEmptyVarSet vs))
+getSRTInfo _               = return False
 
 srt_escape :: StgHalfWord
 srt_escape = -1