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Ben Gamari pushed to branch wip/bco-docs at Glasgow Haskell Compiler / GHC

Commits:

acd08fcd

by Ben Gamari at 2025-05-15T13:05:59-04:00

compiler: Use field selectors when creating BCOs

This makes it easier to grep for these fields.

882ffdec

by Ben Gamari at 2025-05-15T13:06:02-04:00

compiler: Clarify BCO size

Previously the semantics and size of StgBCO was a bit unclear.
Specifically, the `size` field was documented to contain the size of the
bitmap whereas it was actually the size of the closure *and* bitmap.
Additionally, it was not as clear as it could be that the bitmap was a
full StgLargeBitmap with its own `size` field.

4 changed files:

compiler/GHC/ByteCode/Asm.hs
compiler/GHC/ByteCode/Linker.hs
rts/PrimOps.cmm
rts/include/rts/storage/Closures.h

Changes:

compiler/GHC/ByteCode/Asm.hs

@@ -266,7 +266,13 @@ assembleBCO platform
    let !insns_arr =  mkBCOByteArray $ final_isn_array
        !bitmap_arr = mkBCOByteArray $ mkBitmapArray bsize bitmap
 -      ul_bco = UnlinkedBCO nm arity insns_arr bitmap_arr (fromSmallArray final_lit_array) (fromSmallArray final_ptr_array)
 +      ul_bco = UnlinkedBCO { unlinkedBCOName = nm
 +                           , unlinkedBCOArity = arity
 +                           , unlinkedBCOInstrs = insns_arr
 +                           , unlinkedBCOBitmap = bitmap_arr
 +                           , unlinkedBCOLits = fromSmallArray final_lit_array
 +                           , unlinkedBCOPtrs = fromSmallArray final_ptr_array
 +                           }
    -- 8 Aug 01: Finalisers aren't safe when attached to non-primitive
    -- objects, since they might get run too early.  Disable this until
@@ -275,6 +281,7 @@ assembleBCO platform
    return ul_bco
 +-- | Construct a word-array containing an @StgLargeBitmap@.
  mkBitmapArray :: Word -> [StgWord] -> UArray Int Word
  -- Here the return type must be an array of Words, not StgWords,
  -- because the underlying ByteArray# will end up as a component

compiler/GHC/ByteCode/Linker.hs

@@ -65,11 +65,13 @@ linkBCO interp pkgs_loaded le bco_ix
    (lits :: [Word]) <- mapM (fmap fromIntegral . lookupLiteral interp pkgs_loaded le) (elemsFlatBag lits0)
    ptrs <- mapM (resolvePtr interp pkgs_loaded le bco_ix) (elemsFlatBag ptrs0)
    let lits' = listArray (0 :: Int, fromIntegral (sizeFlatBag lits0)-1) lits
 -  return (ResolvedBCO isLittleEndian arity
 -              insns
 -              bitmap
 -              (mkBCOByteArray lits')
 -              (addListToSS emptySS ptrs))
 +  return $ ResolvedBCO { resolvedBCOIsLE   = isLittleEndian
 +                       , resolvedBCOArity  = arity
 +                       , resolvedBCOInstrs = insns
 +                       , resolvedBCOBitmap = bitmap
 +                       , resolvedBCOLits   = mkBCOByteArray lits'
 +                       , resolvedBCOPtrs   = addListToSS emptySS ptrs
 +                       }
  lookupLiteral :: Interp -> PkgsLoaded -> LinkerEnv -> BCONPtr -> IO Word
  lookupLiteral interp pkgs_loaded le ptr = case ptr of

rts/PrimOps.cmm

@@ -2440,6 +2440,7 @@ stg_newBCOzh ( P_ instrs,
                 W_ arity,
                 P_ bitmap_arr )
+ {
 +    // N.B. bitmap_arr contains a full StgLargeBitmap object.
      W_ bco, bytes, words;
      words = BYTES_TO_WDS(SIZEOF_StgBCO) + BYTE_ARR_WDS(bitmap_arr);

rts/include/rts/storage/Closures.h

@@ -427,7 +427,7 @@ typedef struct {
      StgArrBytes   *literals; // literals used by the instructions
      StgMutArrPtrs *ptrs; // free variables
      StgHalfWord   arity; // arity of this BCO
 -    StgHalfWord   size;  // size of the bitmap
 +    StgHalfWord   size;  // size of the closure and bitmap
      StgWord       bitmap[]; // an StgLargeBitmap
  } StgBCO;