StgCmmForeign: Push local register creation into code generation

The interfaces to {save,load}ThreadState were quite messy due to the
need to pass in local registers (produced with draws from a unique
supply) since they were used from both FCode and UniqSM.

This, however, is entirely unnecessary as we already have an
abstraction to capture this effect: MonadUnique. Use it.

This is part of an effort to properly represent stack unwinding
information
for foreign calls.

Test Plan: validate

Reviewers: austin, simonmar

Reviewed By: simonmar

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1733

3 files changed, 59 insertions, 58 deletions

diff --git a/compiler/codeGen/StgCmmForeign.hs b/compiler/codeGen/StgCmmForeign.hs
index 1dc430d06c..cbbf3b64dd 100644
--- a/compiler/codeGen/StgCmmForeign.hs
+++ b/compiler/codeGen/StgCmmForeign.hs
@@ -41,6 +41,7 @@ import ForeignCall
 import DynFlags
 import Maybes
 import Outputable
+import UniqSupply
 import BasicTypes
 
 import Control.Monad
@@ -274,22 +275,20 @@ maybe_assign_temp e = do
 emitSaveThreadState :: FCode ()
 emitSaveThreadState = do
   dflags <- getDynFlags
-  tso <- newTemp (gcWord dflags)
-  cn <- newTemp (bWord dflags)
-  emit $ saveThreadState dflags tso cn
-
+  code <- saveThreadState dflags
+  emit code
 
--- saveThreadState must be usable from the stack layout pass, where we
--- don't have FCode.  Therefore it takes LocalRegs as arguments, so
--- the caller can create these.
-saveThreadState :: DynFlags -> LocalReg -> LocalReg -> CmmAGraph
-saveThreadState dflags tso cn =
-  catAGraphs [
+-- | Produce code to save the current thread state to @CurrentTSO@
+saveThreadState :: MonadUnique m => DynFlags -> m CmmAGraph
+saveThreadState dflags = do
+  tso <- newTemp (gcWord dflags)
+  close_nursery <- closeNursery dflags tso
+  pure $ catAGraphs [
     -- tso = CurrentTSO;
     mkAssign (CmmLocal tso) stgCurrentTSO,
     -- tso->stackobj->sp = Sp;
     mkStore (cmmOffset dflags (CmmLoad (cmmOffset dflags (CmmReg (CmmLocal tso)) (tso_stackobj dflags)) (bWord dflags)) (stack_SP dflags)) stgSp,
-    closeNursery dflags tso cn,
+    close_nursery,
     -- and save the current cost centre stack in the TSO when profiling:
     if gopt Opt_SccProfilingOn dflags then
         mkStore (cmmOffset dflags (CmmReg (CmmLocal tso)) (tso_CCCS dflags)) curCCS
@@ -299,14 +298,18 @@ saveThreadState dflags tso cn =
 emitCloseNursery :: FCode ()
 emitCloseNursery = do
   dflags <- getDynFlags
-  tso <- newTemp (gcWord dflags)
-  cn <- newTemp (bWord dflags)
-  emit $ mkAssign (CmmLocal tso) stgCurrentTSO <*>
-         closeNursery dflags tso cn
+  tso <- newTemp (bWord dflags)
+  code <- closeNursery dflags tso
+  emit $ mkAssign (CmmLocal tso) stgCurrentTSO <*> code
+
+{- |
+@closeNursery dflags tso@ produces code to close the nursery.
+A local register holding the value of @CurrentTSO@ is expected for
+efficiency.
 
-{-
 Closing the nursery corresponds to the following code:
 
+@
   tso = CurrentTSO;
   cn = CurrentNuresry;
 
@@ -318,15 +321,13 @@ Closing the nursery corresponds to the following code:
 
   // Set cn->free to the next unoccupied word in the block
   cn->free = Hp + WDS(1);
+@
 -}
-
-closeNursery :: DynFlags -> LocalReg -> LocalReg -> CmmAGraph
-closeNursery df tso cn =
-  let
-      tsoreg     = CmmLocal tso
-      cnreg      = CmmLocal cn
-  in
-  catAGraphs [
+closeNursery :: MonadUnique m => DynFlags -> LocalReg -> m CmmAGraph
+closeNursery df tso = do
+  let tsoreg  = CmmLocal tso
+  cnreg      <- CmmLocal <$> newTemp (bWord df)
+  pure $ catAGraphs [
     mkAssign cnreg stgCurrentNursery,
 
     -- CurrentNursery->free = Hp+1;
@@ -350,21 +351,16 @@ closeNursery df tso cn =
 emitLoadThreadState :: FCode ()
 emitLoadThreadState = do
   dflags <- getDynFlags
+  code <- loadThreadState dflags
+  emit code
+
+-- | Produce code to load the current thread state from @CurrentTSO@
+loadThreadState :: MonadUnique m => DynFlags -> m CmmAGraph
+loadThreadState dflags = do
   tso <- newTemp (gcWord dflags)
   stack <- newTemp (gcWord dflags)
-  cn <- newTemp (bWord dflags)
-  bdfree <- newTemp (bWord dflags)
-  bdstart <- newTemp (bWord dflags)
-  emit $ loadThreadState dflags tso stack cn bdfree bdstart
-
--- loadThreadState must be usable from the stack layout pass, where we
--- don't have FCode.  Therefore it takes LocalRegs as arguments, so
--- the caller can create these.
-loadThreadState :: DynFlags
-                -> LocalReg -> LocalReg -> LocalReg -> LocalReg -> LocalReg
-                -> CmmAGraph
-loadThreadState dflags tso stack cn bdfree bdstart =
-  catAGraphs [
+  open_nursery <- openNursery dflags tso
+  pure $ catAGraphs [
     -- tso = CurrentTSO;
     mkAssign (CmmLocal tso) stgCurrentTSO,
     -- stack = tso->stackobj;
@@ -378,7 +374,7 @@ loadThreadState dflags tso stack cn bdfree bdstart =
     --   HpAlloc is assumed to be set to non-zero only by a failed
     --   a heap check, see HeapStackCheck.cmm:GC_GENERIC
     mkAssign hpAlloc (zeroExpr dflags),
-    openNursery dflags tso cn bdfree bdstart,
+    open_nursery,
     -- and load the current cost centre stack from the TSO when profiling:
     if gopt Opt_SccProfilingOn dflags
        then storeCurCCS
@@ -391,16 +387,17 @@ loadThreadState dflags tso stack cn bdfree bdstart =
 emitOpenNursery :: FCode ()
 emitOpenNursery = do
   dflags <- getDynFlags
-  tso <- newTemp (gcWord dflags)
-  cn <- newTemp (bWord dflags)
-  bdfree <- newTemp (bWord dflags)
-  bdstart <- newTemp (bWord dflags)
-  emit $ mkAssign (CmmLocal tso) stgCurrentTSO <*>
-         openNursery dflags tso cn bdfree bdstart
+  tso <- newTemp (bWord dflags)
+  code <- openNursery dflags tso
+  emit $ mkAssign (CmmLocal tso) stgCurrentTSO <*> code
+
+{- |
+@openNursery dflags tso@ produces code to open the nursery. A local register
+holding the value of @CurrentTSO@ is expected for efficiency.
 
-{-
 Opening the nursery corresponds to the following code:
 
+@
    tso = CurrentTSO;
    cn = CurrentNursery;
    bdfree = CurrentNuresry->free;
@@ -420,23 +417,20 @@ Opening the nursery corresponds to the following code:
    // Set HpLim to the end of the current nursery block (note that this block
    // might be a block group, consisting of several adjacent blocks.
    HpLim = bdstart + CurrentNursery->blocks*BLOCK_SIZE_W - 1;
+@
 -}
+openNursery :: MonadUnique m => DynFlags -> LocalReg -> m CmmAGraph
+openNursery df tso = do
+  let tsoreg =  CmmLocal tso
+  cnreg      <- CmmLocal <$> newTemp (bWord df)
+  bdfreereg  <- CmmLocal <$> newTemp (bWord df)
+  bdstartreg <- CmmLocal <$> newTemp (bWord df)
 
-openNursery :: DynFlags
-            -> LocalReg -> LocalReg -> LocalReg -> LocalReg
-            -> CmmAGraph
-openNursery df tso cn bdfree bdstart =
-  let
-      tsoreg     = CmmLocal tso
-      cnreg      = CmmLocal cn
-      bdfreereg  = CmmLocal bdfree
-      bdstartreg = CmmLocal bdstart
-  in
   -- These assignments are carefully ordered to reduce register
   -- pressure and generate not completely awful code on x86.  To see
   -- what code we generate, look at the assembly for
   -- stg_returnToStackTop in rts/StgStartup.cmm.
-  catAGraphs [
+  pure $ catAGraphs [
      mkAssign cnreg stgCurrentNursery,
      mkAssign bdfreereg  (CmmLoad (nursery_bdescr_free df cnreg)  (bWord df)),
 
diff --git a/compiler/codeGen/StgCmmMonad.hs b/compiler/codeGen/StgCmmMonad.hs
index 6611b2944e..42033200c8 100644
--- a/compiler/codeGen/StgCmmMonad.hs
+++ b/compiler/codeGen/StgCmmMonad.hs
@@ -127,6 +127,12 @@ instance Monad FCode where
 {-# INLINE thenFC #-}
 {-# INLINE returnFC #-}
 
+instance MonadUnique FCode where
+  getUniqueSupplyM = cgs_uniqs <$> getState
+  getUniqueM = FCode $ \_ st ->
+    let (u, us') = takeUniqFromSupply (cgs_uniqs st)
+    in (# u, st { cgs_uniqs = us' } #)
+
 initC :: IO CgState
 initC  = do { uniqs <- mkSplitUniqSupply 'c'
             ; return (initCgState uniqs) }
diff --git a/compiler/codeGen/StgCmmUtils.hs b/compiler/codeGen/StgCmmUtils.hs
index b4dd869039..a98ce739fd 100644
--- a/compiler/codeGen/StgCmmUtils.hs
+++ b/compiler/codeGen/StgCmmUtils.hs
@@ -63,6 +63,7 @@ import Literal
 import Digraph
 import Util
 import Unique
+import UniqSupply (MonadUnique(..))
 import DynFlags
 import FastString
 import Outputable
@@ -345,8 +346,8 @@ assignTemp e = do { dflags <- getDynFlags
                   ; emitAssign (CmmLocal reg) e
                   ; return reg }
 
-newTemp :: CmmType -> FCode LocalReg
-newTemp rep = do { uniq <- newUnique
+newTemp :: MonadUnique m => CmmType -> m LocalReg
+newTemp rep = do { uniq <- getUniqueM
                  ; return (LocalReg uniq rep) }
 
 newUnboxedTupleRegs :: Type -> FCode ([LocalReg], [ForeignHint])