[Git][ghc/ghc][wip/mpickering-hannes] Force inner_bh outside of unsafeInterleaveIO

[Matthew Pickering (@mpickering)]

Matthew Pickering pushed to branch wip/mpickering-hannes at Glasgow Haskell Compiler / GHC


Commits:
4ef9f2b1 by Matthew Pickering at 2024-03-23T15:59:39+00:00
Force inner_bh outside of unsafeInterleaveIO

This reduces the size of the FUN closure from 96 to 56 bytes.

Which saves ~12mb live bytes overall.

- - - - -


1 changed file:

- compiler/GHC/Utils/Binary.hs


Changes:

=====================================
compiler/GHC/Utils/Binary.hs
=====================================
@@ -1144,15 +1144,17 @@ lazyGet' :: HasCallStack => Maybe (IORef BinHandle) -> (Bin () -> BinHandle -> I
 lazyGet' mbh f bh = do
     p <- get @(Bin ()) bh -- a BinPtr
     p_a <- tellBin bh
+    -- Do this before to avoid retaining reference to old BH inside the unsafeInterleaveIO.
+    let !get_inner_bh = maybe (pure bh) readIORef mbh
     a <- unsafeInterleaveIO $ do
         -- NB: Use a fresh off_r variable in the child thread, for thread
         -- safety.
-        inner_bh <- maybe (pure bh) readIORef mbh
+        inner_bh <- get_inner_bh
         off_r <- newFastMutInt 0
         let bh' = inner_bh { _off_r = off_r }
-        seekBin bh' p_a
+        seekBinNoExpand bh' p_a
         f p bh'
-    seekBin bh p -- skip over the object for now
+    seekBinNoExpand bh p -- skip over the object for now
     return a
 
 -- | Serialize the constructor strictly but lazily serialize a value inside a
@@ -1282,6 +1284,8 @@ getGenericSymbolTable :: forall a. (Bin () -> BinHandle -> IO a) -> IORef BinHan
 getGenericSymbolTable deserialiser bhRef bh = do
   sz <- forwardGet bh (get bh) :: IO Int
   mut_arr <- newArray_ (0, sz-1) :: IO (IOArray Int a)
+  -- Using lazyPut/lazyGet is quite space inefficient as each usage will allocate a large closure
+  -- (6 arguments-ish).
   forM_ [0..(sz-1)] $ \i -> do
     f <- lazyGet' (Just bhRef) deserialiser bh
     writeArray mut_arr i f



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/4ef9f2b17f1ef12e735475a21c99564135176632

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/4ef9f2b17f1ef12e735475a21c99564135176632
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