diff options
Diffstat (limited to 'compiler/GHC/CmmToAsm/Monad.hs')
| -rw-r--r-- | compiler/GHC/CmmToAsm/Monad.hs | 38 |
1 files changed, 36 insertions, 2 deletions
diff --git a/compiler/GHC/CmmToAsm/Monad.hs b/compiler/GHC/CmmToAsm/Monad.hs index eb445649c3..2a61ff0314 100644 --- a/compiler/GHC/CmmToAsm/Monad.hs +++ b/compiler/GHC/CmmToAsm/Monad.hs @@ -67,7 +67,7 @@ import GHC.Types.Unique.Supply import GHC.Types.Unique ( Unique ) import GHC.Unit.Module -import GHC.Utils.Outputable (SDoc, ppr) +import GHC.Utils.Outputable (SDoc, HDoc, ppr) import GHC.Utils.Panic (pprPanic) import GHC.Utils.Monad.State.Strict (State (..), runState, state) import GHC.Utils.Misc @@ -84,7 +84,9 @@ data NcgImpl statics instr jumpDest = NcgImpl { shortcutJump :: (BlockId -> Maybe jumpDest) -> instr -> instr, -- | 'Module' is only for printing internal labels. See Note [Internal proc -- labels] in CLabel. - pprNatCmmDecl :: NatCmmDecl statics instr -> SDoc, + pprNatCmmDeclS :: NatCmmDecl statics instr -> SDoc, + pprNatCmmDeclH :: NatCmmDecl statics instr -> HDoc, + -- see Note [pprNatCmmDeclS and pprNatCmmDeclH] maxSpillSlots :: Int, allocatableRegs :: [RealReg], ncgAllocMoreStack :: Int -> NatCmmDecl statics instr @@ -103,6 +105,38 @@ data NcgImpl statics instr jumpDest = NcgImpl { -- when possible. } +{- Note [pprNatCmmDeclS and pprNatCmmDeclH] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Each NcgImpl provides two implementations of its CmmDecl printer, pprNatCmmDeclS +and pprNatCmmDeclH, which are specialized to SDoc and HDoc, respectively +(see Note [SDoc versus HDoc] in GHC.Utils.Outputable). These are both internally +implemented as a single, polymorphic function, but they need to be stored using +monomorphic types to ensure the specialized versions are used, which is +essential for performance (see Note [SPECIALIZE to HDoc] in GHC.Utils.Outputable). + +One might wonder why we bother with pprNatCmmDeclS and SDoc at all, since we +have a perfectly serviceable HDoc-based implementation that is more efficient. +However, it turns out we benefit from keeping both, for two (related) reasons: + + 1. Although we absolutely want to take care to use pprNatCmmDeclH for actual + code generation (the improved performance there is why we have HDoc at + all!), we also sometimes print assembly for debug dumps, when requested via + -ddump-asm. In this case, it’s more convenient to produce an SDoc, which + can be concatenated with other SDocs for consistency with the general- + purpose dump file infrastructure. + + 2. Some debug information is sometimes useful to include in -ddump-asm that is + neither necessary nor useful in normal code generation, and it turns out to + be tricky to format neatly using the one-line-at-a-time model of HLine/HDoc. + +Therefore, we provide both pprNatCmmDeclS and pprNatCmmDeclH, and we sometimes +include additional information in the SDoc variant using dualDoc +(see Note [dualLine and dualDoc] in GHC.Utils.Outputable). However, it is +absolutely *critical* that pprNatCmmDeclS is not actually used unless -ddump-asm +is provided, as that would rather defeat the whole point. (Fortunately, the +difference in allocations between the two implementations is so vast that such a +mistake would readily show up in performance tests). -} + data NatM_State = NatM_State { natm_us :: UniqSupply, |