[Git][ghc/ghc][wip/ioref-swap-xchg] compiler: Implement atomicSwapIORef with xchg

[Ben Gamari (@bgamari)]

Ben Gamari pushed to branch wip/ioref-swap-xchg at Glasgow Haskell Compiler / GHC


Commits:
873cfa51 by Ben Gamari at 2023-03-24T00:15:11-04:00
compiler: Implement atomicSwapIORef with xchg

- - - - -


8 changed files:

- compiler/GHC/Builtin/primops.txt.pp
- compiler/GHC/StgToCmm/Prim.hs
- compiler/GHC/StgToJS/Prim.hs
- libraries/base/GHC/IORef.hs
- rts/PrimOps.cmm
- rts/RtsSymbols.c
- rts/include/Cmm.h
- rts/include/stg/MiscClosures.h


Changes:

=====================================
compiler/GHC/Builtin/primops.txt.pp
=====================================
@@ -2513,6 +2513,13 @@ primop  WriteMutVarOp "writeMutVar#"  GenPrimOp
    has_side_effects = True
    code_size = { primOpCodeSizeForeignCall } -- for the write barrier
 
+primop  AtomicSwapMutVarOp "atomicSwapMutVar#" GenPrimOp
+   MutVar# s v -> v -> State# s -> (# State# s, v #)
+   {Atomically exchange the value of a 'MutVar#'.}
+   with
+   out_of_line = True
+   has_side_effects = True
+
 -- Note [Why not an unboxed tuple in atomicModifyMutVar2#?]
 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 -- Looking at the type of atomicModifyMutVar2#, one might wonder why


=====================================
compiler/GHC/StgToCmm/Prim.hs
=====================================
@@ -1559,6 +1559,7 @@ emitPrimOp cfg primop =
   ResizeMutableByteArrayOp_Char -> alwaysExternal
   ShrinkSmallMutableArrayOp_Char -> alwaysExternal
   NewMutVarOp -> alwaysExternal
+  AtomicSwapMutVarOp -> alwaysExternal
   AtomicModifyMutVar2Op -> alwaysExternal
   AtomicModifyMutVar_Op -> alwaysExternal
   CasMutVarOp -> alwaysExternal


=====================================
compiler/GHC/StgToJS/Prim.hs
=====================================
@@ -859,6 +859,8 @@ genPrim prof bound ty op = case op of
   AtomicModifyMutVar2Op -> \[r1,r2] [m,f] -> PrimInline $ appT [r1,r2] "h$atomicModifyMutVar2" [m,f]
   AtomicModifyMutVar_Op -> \[r1,r2] [m,f] -> PrimInline $ appT [r1,r2] "h$atomicModifyMutVar" [m,f]
 
+  AtomicSwapMutVarOp    -> \[r] [mv,v] -> PrimInline $ mconcat
+                                                [ r |= mv .^ "val", mv .^ "val" |= v ]
   CasMutVarOp -> \[status,r] [mv,o,n] -> PrimInline $ ifS (mv .^ "val" .===. o)
                    (mconcat [status |= zero_, r |= n, mv .^ "val" |= n])
                    (mconcat [status |= one_ , r |= mv .^ "val"])


=====================================
libraries/base/GHC/IORef.hs
=====================================
@@ -127,12 +127,9 @@ atomicModifyIORef'_ ref f = do
 -- | Atomically replace the contents of an 'IORef', returning
 -- the old contents.
 atomicSwapIORef :: IORef a -> a -> IO a
--- Bad implementation! This will be a primop shortly.
 atomicSwapIORef (IORef (STRef ref)) new = IO $ \s ->
-  case atomicModifyMutVar2# ref (\_old -> Box new) s of
-    (# s', old, Box _new #) -> (# s', old #)
-
-data Box a = Box a
+  case atomicSwapMutVar# ref new s of
+    (# s', old #) -> (# s', old #)
 
 -- | Strict version of 'Data.IORef.atomicModifyIORef'. This forces both
 -- the value stored in the 'IORef' and the value returned. The new value


=====================================
rts/PrimOps.cmm
=====================================
@@ -689,6 +689,17 @@ stg_newMutVarzh ( gcptr init )
     return (mv);
 }
 
+stg_atomicSwapMutVarzh ( gcptr mv, gcptr new )
+ /* MutVar# s a -> a -> State# s -> (# State#, a #) */
+{
+    W_ old;
+    (old) = prim %xchgW(mv + SIZEOF_StgHeader + OFFSET_StgMutVar_var, new);
+    if (GET_INFO(mv) == stg_MUT_VAR_CLEAN_info) {
+        ccall dirty_MUT_VAR(BaseReg "ptr", mv "ptr", old "ptr");
+    }
+    return (old);
+}
+
 // RRN: To support the "ticketed" approach, we return the NEW rather
 // than old value if the CAS is successful.  This is received in an
 // opaque form in the Haskell code, preventing the compiler from


=====================================
rts/RtsSymbols.c
=====================================
@@ -633,6 +633,7 @@ extern char **environ;
       SymI_HasDataProto(stg_writeIOPortzh)                                  \
       SymI_HasDataProto(stg_newIOPortzh)                                    \
       SymI_HasDataProto(stg_noDuplicatezh)                                  \
+      SymI_HasDataProto(stg_atomicSwapMutVarzh)                             \
       SymI_HasDataProto(stg_atomicModifyMutVar2zh)                          \
       SymI_HasDataProto(stg_atomicModifyMutVarzuzh)                         \
       SymI_HasDataProto(stg_casMutVarzh)                                    \


=====================================
rts/include/Cmm.h
=====================================
@@ -193,8 +193,10 @@
 
 #if SIZEOF_W == 4
 #define cmpxchgW cmpxchg32
+#define xchgW xchg32
 #elif SIZEOF_W == 8
 #define cmpxchgW cmpxchg64
+#define xchgW xchg64
 #endif
 
 /* -----------------------------------------------------------------------------


=====================================
rts/include/stg/MiscClosures.h
=====================================
@@ -481,6 +481,7 @@ RTS_FUN_DECL(stg_copySmallMutableArrayzh);
 RTS_FUN_DECL(stg_casSmallArrayzh);
 
 RTS_FUN_DECL(stg_newMutVarzh);
+RTS_FUN_DECL(stg_atomicSwapMutVarzh);
 RTS_FUN_DECL(stg_atomicModifyMutVar2zh);
 RTS_FUN_DECL(stg_atomicModifyMutVarzuzh);
 RTS_FUN_DECL(stg_casMutVarzh);



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/873cfa51f3b49dfc8c4923456c10c7eb9d3cfef2

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/873cfa51f3b49dfc8c4923456c10c7eb9d3cfef2
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