diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/cmm/CmmLayoutStack.hs | 24 |
1 files changed, 12 insertions, 12 deletions
diff --git a/compiler/cmm/CmmLayoutStack.hs b/compiler/cmm/CmmLayoutStack.hs index 4ac5725df1..2efb806a1e 100644 --- a/compiler/cmm/CmmLayoutStack.hs +++ b/compiler/cmm/CmmLayoutStack.hs @@ -773,24 +773,24 @@ areaToSp :: DynFlags -> ByteOff -> ByteOff -> (Area -> StackLoc) -> CmmExpr -> C areaToSp dflags sp_old _sp_hwm area_off (CmmStackSlot area n) = cmmOffset dflags (CmmReg spReg) (sp_old - area_off area - n) areaToSp dflags _ sp_hwm _ (CmmLit CmmHighStackMark) = mkIntExpr dflags sp_hwm -areaToSp dflags _ _ _ (CmmMachOp (MO_U_Lt _) -- Note [null stack check] +areaToSp dflags _ _ _ (CmmMachOp (MO_U_Lt _) -- Note [Always false stack check] [CmmMachOp (MO_Sub _) - [ CmmReg (CmmGlobal Sp) - , CmmLit (CmmInt 0 _)], - CmmReg (CmmGlobal SpLim)]) = zeroExpr dflags + [ CmmRegOff (CmmGlobal Sp) off + , CmmLit (CmmInt lit _)], + CmmReg (CmmGlobal SpLim)]) + | fromIntegral off == lit = zeroExpr dflags areaToSp _ _ _ _ other = other --- ----------------------------------------------------------------------------- --- Note [null stack check] +-- Note [Always false stack check] +-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- --- If the high-water Sp is zero, then we end up with +-- We can optimise stack checks of the form -- --- if (Sp - 0 < SpLim) then .. else .. +-- if ((Sp + x) - x < SpLim) then .. else .. -- --- and possibly some dead code for the failure case. Optimising this --- away depends on knowing that SpLim <= Sp, so it is really the job --- of the stack layout algorithm, hence we do it now. This is also --- convenient because control-flow optimisation later will drop the +-- where x is an integer offset. Optimising this away depends on knowing that +-- SpLim <= Sp, so it is really the job of the stack layout algorithm, hence we +-- do it now. This is also convenient because sinking pass will later drop the -- dead code. optStackCheck :: CmmNode O C -> CmmNode O C |