diff options
Diffstat (limited to 'compiler/codeGen')
| -rw-r--r-- | compiler/codeGen/StgCmmHeap.hs | 2 | ||||
| -rw-r--r-- | compiler/codeGen/StgCmmLayout.hs | 5 | ||||
| -rw-r--r-- | compiler/codeGen/StgCmmMonad.hs | 36 |
3 files changed, 37 insertions, 6 deletions
diff --git a/compiler/codeGen/StgCmmHeap.hs b/compiler/codeGen/StgCmmHeap.hs index 488a0e05bc..a3a47a65e7 100644 --- a/compiler/codeGen/StgCmmHeap.hs +++ b/compiler/codeGen/StgCmmHeap.hs @@ -8,7 +8,7 @@ module StgCmmHeap ( getVirtHp, setVirtHp, setRealHp, - getHpRelOffset, hpRel, + getHpRelOffset, entryHeapCheck, altHeapCheck, noEscapeHeapCheck, altHeapCheckReturnsTo, heapStackCheckGen, diff --git a/compiler/codeGen/StgCmmLayout.hs b/compiler/codeGen/StgCmmLayout.hs index 7fbcbced81..59afc897dc 100644 --- a/compiler/codeGen/StgCmmLayout.hs +++ b/compiler/codeGen/StgCmmLayout.hs @@ -15,7 +15,7 @@ module StgCmmLayout ( slowCall, directCall, - mkVirtHeapOffsets, mkVirtConstrOffsets, getHpRelOffset, hpRel, + mkVirtHeapOffsets, mkVirtConstrOffsets, getHpRelOffset, ArgRep(..), toArgRep, argRepSizeW -- re-exported from StgCmmArgRep ) where @@ -366,13 +366,14 @@ slowArgs dflags args -- careful: reps contains voids (V), but args does not ---- Laying out objects on the heap and stack ------------------------------------------------------------------------- --- The heap always grows upwards, so hpRel is easy +-- The heap always grows upwards, so hpRel is easy to compute hpRel :: VirtualHpOffset -- virtual offset of Hp -> VirtualHpOffset -- virtual offset of The Thing -> WordOff -- integer word offset hpRel hp off = off - hp getHpRelOffset :: VirtualHpOffset -> FCode CmmExpr +-- See Note [Virtual and real heap pointers] in StgCmmMonad getHpRelOffset virtual_offset = do dflags <- getDynFlags hp_usg <- getHpUsage diff --git a/compiler/codeGen/StgCmmMonad.hs b/compiler/codeGen/StgCmmMonad.hs index 3d82e69402..348b7b9299 100644 --- a/compiler/codeGen/StgCmmMonad.hs +++ b/compiler/codeGen/StgCmmMonad.hs @@ -331,17 +331,47 @@ data CgState cgs_uniqs :: UniqSupply } -data HeapUsage = - HeapUsage { +data HeapUsage -- See Note [Virtual and real heap pointers] + = HeapUsage { virtHp :: VirtualHpOffset, -- Virtual offset of highest-allocated word -- Incremented whenever we allocate realHp :: VirtualHpOffset -- realHp: Virtual offset of real heap ptr -- Used in instruction addressing modes - } + } type VirtualHpOffset = WordOff +{- Note [Virtual and real heap pointers] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The code generator can allocate one or more objects contiguously, performing +one heap check to cover allocation of all the objects at once. Let's call +this little chunk of heap space an "allocation chunk". The code generator +will emit code to + * Perform a heap-exhaustion check + * Move the heap pointer to the end of the allocation chunk + * Allocate multiple objects within the chunk + +The code generator uses VirtualHpOffsets to address words within a +single allocation chunk; these start at one and increase positively. +The first word of the chunk has VirtualHpOffset=1, the second has +VirtualHpOffset=2, and so on. + + * The field realHp tracks (the VirtualHpOffset) where the real Hp + register is pointing. Typically it'll be pointing to the end of the + allocation chunk. + + * The field virtHp gives the VirtualHpOffset of the highest-allocated + word so far. It starts at zero (meaning no word has been allocated), + and increases whenever an object is allocated. + +The difference between realHp and virtHp gives the offset from the +real Hp register of a particular word in the allocation chunk. This +is what getHpRelOffset does. Since the returned offset is relative +to the real Hp register, it is valid only until you change the real +Hp register. (Changing virtHp doesn't matter.) +-} + initCgState :: UniqSupply -> CgState initCgState uniqs |