Change the way module initialisation is done (#3252, #4417)

Previously the code generator generated small code fragments labelled
with __stginit_M for each module M, and these performed whatever
initialisation was necessary for that module and recursively invoked
the initialisation functions for imported modules.  This appraoch had
drawbacks:

 - FFI users had to call hs_add_root() to ensure the correct
   initialisation routines were called.  This is a non-standard,
   and ugly, API.

 - unless we were using -split-objs, the __stginit dependencies would
   entail linking the whole transitive closure of modules imported,
   whether they were actually used or not.  In an extreme case (#4387,
   #4417), a module from GHC might be imported for use in Template
   Haskell or an annotation, and that would force the whole of GHC to
   be needlessly linked into the final executable.

So now instead we do our initialisation with C functions marked with
__attribute__((constructor)), which are automatically invoked at
program startup time (or DSO load-time).  The C initialisers are
emitted into the stub.c file.  This means that every time we compile
with -prof or -hpc, we now get a stub file, but thanks to #3687 that
is now invisible to the user.

There are some refactorings in the RTS (particularly for HPC) to
handle the fact that initialisers now get run earlier than they did
before.

The __stginit symbols are still generated, and the hs_add_root()
function still exists (but does nothing), for backwards compatibility.

1 files changed, 22 insertions, 148 deletions

diff --git a/compiler/codeGen/CodeGen.lhs b/compiler/codeGen/CodeGen.lhs
index 6ce8fca55b..81a65f7325 100644
--- a/compiler/codeGen/CodeGen.lhs
+++ b/compiler/codeGen/CodeGen.lhs
@@ -29,7 +29,6 @@ import CgHpc
 
 import CLabel
 import OldCmm
-import OldCmmUtils
 import OldPprCmm
 
 import StgSyn
@@ -51,8 +50,7 @@ import Panic
 codeGen :: DynFlags
 	-> Module
 	-> [TyCon]
-	-> [Module]		-- directly-imported modules
-	-> CollectedCCs		-- (Local/global) cost-centres needing declaring/registering.
+        -> CollectedCCs         -- (Local/global) cost-centres needing declaring/registering.
 	-> [(StgBinding,[(Id,[Id])])]	-- Bindings to convert, with SRTs
 	-> HpcInfo
 	-> IO [Cmm]		-- Output
@@ -61,8 +59,7 @@ codeGen :: DynFlags
                 -- possible for object splitting to split up the
                 -- pieces later.
 
-codeGen dflags this_mod data_tycons imported_mods 
-	cost_centre_info stg_binds hpc_info
+codeGen dflags this_mod data_tycons cost_centre_info stg_binds hpc_info
   = do	
   { showPass dflags "CodeGen"
 
@@ -73,167 +70,46 @@ codeGen dflags this_mod data_tycons imported_mods
 		{ cmm_binds  <- mapM (getCmm . cgTopBinding dflags) stg_binds
 		; cmm_tycons <- mapM cgTyCon data_tycons
 		; cmm_init   <- getCmm (mkModuleInit dflags cost_centre_info 
-					     this_mod imported_mods hpc_info)
-		; return (cmm_binds ++ concat cmm_tycons ++ [cmm_init])
+                                             this_mod hpc_info)
+                ; return (cmm_init : cmm_binds ++ concat cmm_tycons)
 		}
 		-- Put datatype_stuff after code_stuff, because the
 		-- datatype closure table (for enumeration types) to
 		-- (say) PrelBase_True_closure, which is defined in
 		-- code_stuff
 
+                -- Note [codegen-split-init] the cmm_init block must
+                -- come FIRST.  This is because when -split-objs is on
+                -- we need to combine this block with its
+                -- initialisation routines; see Note
+                -- [pipeline-split-init].
+
   ; dumpIfSet_dyn dflags Opt_D_dump_cmm "Cmm" (pprCmms code_stuff)
 
   ; return code_stuff }
-\end{code}
-
-%************************************************************************
-%*									*
-\subsection[codegen-init]{Module initialisation code}
-%*									*
-%************************************************************************
-
-/* -----------------------------------------------------------------------------
-   Module initialisation
-
-   The module initialisation code looks like this, roughly:
-
-	FN(__stginit_Foo) {
- 	  JMP_(__stginit_Foo_1_p)
-	}
-
-	FN(__stginit_Foo_1_p) {
-	...
-	}
-
-   We have one version of the init code with a module version and the
-   'way' attached to it.  The version number helps to catch cases
-   where modules are not compiled in dependency order before being
-   linked: if a module has been compiled since any modules which depend on
-   it, then the latter modules will refer to a different version in their
-   init blocks and a link error will ensue.
-
-   The 'way' suffix helps to catch cases where modules compiled in different
-   ways are linked together (eg. profiled and non-profiled).
-
-   We provide a plain, unadorned, version of the module init code
-   which just jumps to the version with the label and way attached.  The
-   reason for this is that when using foreign exports, the caller of
-   startupHaskell() must supply the name of the init function for the "top"
-   module in the program, and we don't want to require that this name
-   has the version and way info appended to it.
-   --------------------------------------------------------------------------  */
-
-We initialise the module tree by keeping a work-stack, 
-	* pointed to by Sp
-	* that grows downward
-	* Sp points to the last occupied slot
-
 
-\begin{code}
-mkModuleInit 
+mkModuleInit
         :: DynFlags
 	-> CollectedCCs         -- cost centre info
 	-> Module
-	-> [Module]
-	-> HpcInfo
+        -> HpcInfo
 	-> Code
-mkModuleInit dflags cost_centre_info this_mod imported_mods hpc_info
-  = do	{ -- Allocate the static boolean that records if this
-          -- module has been registered already
-	  emitData Data [CmmDataLabel moduleRegdLabel, 
-		         CmmStaticLit zeroCLit]
 
+mkModuleInit dflags cost_centre_info this_mod hpc_info
+  = do	{ -- Allocate the static boolean that records if this
         ; whenC (opt_Hpc) $
               hpcTable this_mod hpc_info
 
-          -- we emit a recursive descent module search for all modules
-	  -- and *choose* to chase it in :Main, below.
-          -- In this way, Hpc enabled modules can interact seamlessly with
-	  -- not Hpc enabled moduled, provided Main is compiled with Hpc.
-
-        ; emitSimpleProc real_init_lbl $ do
-                       { ret_blk <- forkLabelledCode ret_code
-
-                        ; init_blk <- forkLabelledCode $ do
-                                        { mod_init_code; stmtC (CmmBranch ret_blk) }
-                                    
-                        ; stmtC (CmmCondBranch (cmmNeWord (CmmLit zeroCLit) mod_reg_val)
-                                    ret_blk)
-                        ; stmtC (CmmBranch init_blk)	    
-                        }
-
- 	    -- Make the "plain" procedure jump to the "real" init procedure
-	; emitSimpleProc plain_init_lbl jump_to_init
-
-	-- When compiling the module in which the 'main' function lives,
-	-- (that is, this_mod == main_mod)
-	-- we inject an extra stg_init procedure for stg_init_ZCMain, for the 
-	-- RTS to invoke.  We must consult the -main-is flag in case the
-	-- user specified a different function to Main.main
- 
-        -- Notice that the recursive descent is optional, depending on what options
-	-- are enabled.
-
-	; whenC (this_mod == main_mod)
-		(emitSimpleProc plain_main_init_lbl rec_descent_init)
-    }
-  where
-    -- The way string we attach to the __stginit label to catch
-    -- accidental linking of modules compiled in different ways.  We
-    -- omit "dyn" from this way, because we want to be able to load
-    -- both dynamic and non-dynamic modules into a dynamic GHC.
-    way = mkBuildTag (filter want_way (ways dflags))
-    want_way w = not (wayRTSOnly w) && wayName w /= WayDyn
-
-    main_mod = mainModIs dflags
-
-    plain_init_lbl = mkPlainModuleInitLabel this_mod
-    real_init_lbl  = mkModuleInitLabel this_mod way
-    plain_main_init_lbl = mkPlainModuleInitLabel rOOT_MAIN
-
-    jump_to_init = stmtC (CmmJump (mkLblExpr real_init_lbl) [])
-
-    mod_reg_val = CmmLoad (mkLblExpr moduleRegdLabel) bWord
-
-    -- Main refers to GHC.TopHandler.runIO, so make sure we call the
-    -- init function for GHC.TopHandler.
-    extra_imported_mods
-	| this_mod == main_mod = [gHC_TOP_HANDLER]
-	| otherwise	       = []
-
-    mod_init_code = do
-	{ 	-- Set mod_reg to 1 to record that we've been here
-	  stmtC (CmmStore (mkLblExpr moduleRegdLabel) (CmmLit (mkIntCLit 1)))
-
         ; whenC (opt_SccProfilingOn) $ do 
 	    initCostCentres cost_centre_info
 
-        ; whenC (opt_Hpc) $
-            initHpc this_mod hpc_info
-         
-	; mapCs (registerModuleImport way)
-		(imported_mods++extra_imported_mods)
-
-	} 
-
-                    -- The return-code pops the work stack by 
-                    -- incrementing Sp, and then jumpd to the popped item
-    ret_code = stmtsC [ CmmAssign spReg (cmmRegOffW spReg 1)
-                      , CmmJump (CmmLoad (cmmRegOffW spReg (-1)) bWord) [] ]
-
-
-    rec_descent_init = if opt_SccProfilingOn || isHpcUsed hpc_info
-		       then jump_to_init
-		       else ret_code
-
------------------------
-registerModuleImport :: String -> Module -> Code
-registerModuleImport way mod
-  | mod == gHC_PRIM
-  = nopC 
-  | otherwise 	-- Push the init procedure onto the work stack
-  = stmtsC [ CmmAssign spReg (cmmRegOffW spReg (-1))
-	   , CmmStore (CmmReg spReg) (mkLblExpr (mkModuleInitLabel mod way)) ]
+            -- For backwards compatibility: user code may refer to this
+            -- label for calling hs_add_root().
+        ; emitSimpleProc (mkPlainModuleInitLabel this_mod) $ return ()
+
+        ; whenC (this_mod == mainModIs dflags) $
+             emitSimpleProc (mkPlainModuleInitLabel rOOT_MAIN) $ return ()
+    }
 \end{code}
 
 
@@ -252,9 +128,7 @@ initCostCentres (local_CCs, ___extern_CCs, singleton_CCSs)
   | otherwise
   = do	{ mapM_ emitCostCentreDecl  	 local_CCs
 	; mapM_ emitCostCentreStackDecl  singleton_CCSs
-	; mapM_ emitRegisterCC           local_CCs
-	; mapM_ emitRegisterCCS          singleton_CCSs
-	}
+        }
 \end{code}
 
 %************************************************************************