diff options
Diffstat (limited to 'compiler/cmm/CmmOpt.hs')
| -rw-r--r-- | compiler/cmm/CmmOpt.hs | 83 |
1 files changed, 57 insertions, 26 deletions
diff --git a/compiler/cmm/CmmOpt.hs b/compiler/cmm/CmmOpt.hs index 38c399ebc4..3cb28217f2 100644 --- a/compiler/cmm/CmmOpt.hs +++ b/compiler/cmm/CmmOpt.hs @@ -284,48 +284,68 @@ cmmMachOpFoldM dflags cmp [CmmMachOp conv [x], CmmLit (CmmInt i _)] maybe_comparison _ _ _ = Nothing -- We can often do something with constants of 0 and 1 ... +-- See Note [Comparison operators] cmmMachOpFoldM dflags mop [x, y@(CmmLit (CmmInt 0 _))] = case mop of - MO_Add _ -> Just x - MO_Sub _ -> Just x - MO_Mul _ -> Just y - MO_And _ -> Just y - MO_Or _ -> Just x - MO_Xor _ -> Just x - MO_Shl _ -> Just x - MO_S_Shr _ -> Just x + -- Arithmetic + MO_Add _ -> Just x -- x + 0 = x + MO_Sub _ -> Just x -- x - 0 = x + MO_Mul _ -> Just y -- x * 0 = 0 + + -- Logical operations + MO_And _ -> Just y -- x & 0 = 0 + MO_Or _ -> Just x -- x | 0 = x + MO_Xor _ -> Just x -- x `xor` 0 = x + + -- Shifts + MO_Shl _ -> Just x -- x << 0 = x + MO_S_Shr _ -> Just x -- ditto shift-right MO_U_Shr _ -> Just x - MO_Ne _ | isComparisonExpr x -> Just x - MO_Eq _ | Just x' <- maybeInvertCmmExpr x -> Just x' - MO_U_Gt _ | isComparisonExpr x -> Just x - MO_S_Gt _ | isComparisonExpr x -> Just x - MO_U_Lt _ | isComparisonExpr x -> Just $ CmmLit (CmmInt 0 (wordWidth dflags)) - MO_S_Lt _ | isComparisonExpr x -> Just $ CmmLit (CmmInt 0 (wordWidth dflags)) - MO_U_Ge _ | isComparisonExpr x -> Just $ CmmLit (CmmInt 1 (wordWidth dflags)) - MO_S_Ge _ | isComparisonExpr x -> Just $ CmmLit (CmmInt 1 (wordWidth dflags)) - MO_U_Le _ | Just x' <- maybeInvertCmmExpr x -> Just x' + + -- Comparisons; these ones are trickier + -- See Note [Comparison operators] + MO_Ne _ | isComparisonExpr x -> Just x -- (x > y) != 0 = x > y + MO_Eq _ | Just x' <- maybeInvertCmmExpr x -> Just x' -- (x > y) == 0 = x <= y + MO_U_Gt _ | isComparisonExpr x -> Just x -- (x > y) > 0 = x > y + MO_S_Gt _ | isComparisonExpr x -> Just x -- ditto + MO_U_Lt _ | isComparisonExpr x -> Just zero -- (x > y) < 0 = 0 + MO_S_Lt _ | isComparisonExpr x -> Just zero + MO_U_Ge _ | isComparisonExpr x -> Just one -- (x > y) >= 0 = 1 + MO_S_Ge _ | isComparisonExpr x -> Just one + + MO_U_Le _ | Just x' <- maybeInvertCmmExpr x -> Just x' -- (x > y) <= 0 = x <= y MO_S_Le _ | Just x' <- maybeInvertCmmExpr x -> Just x' _ -> Nothing + where + zero = CmmLit (CmmInt 0 (wordWidth dflags)) + one = CmmLit (CmmInt 1 (wordWidth dflags)) cmmMachOpFoldM dflags mop [x, (CmmLit (CmmInt 1 rep))] = case mop of + -- Arithmetic: x*1 = x, etc MO_Mul _ -> Just x MO_S_Quot _ -> Just x MO_U_Quot _ -> Just x MO_S_Rem _ -> Just $ CmmLit (CmmInt 0 rep) MO_U_Rem _ -> Just $ CmmLit (CmmInt 0 rep) - MO_Ne _ | Just x' <- maybeInvertCmmExpr x -> Just x' - MO_Eq _ | isComparisonExpr x -> Just x - MO_U_Lt _ | Just x' <- maybeInvertCmmExpr x -> Just x' - MO_S_Lt _ | Just x' <- maybeInvertCmmExpr x -> Just x' - MO_U_Gt _ | isComparisonExpr x -> Just $ CmmLit (CmmInt 0 (wordWidth dflags)) - MO_S_Gt _ | isComparisonExpr x -> Just $ CmmLit (CmmInt 0 (wordWidth dflags)) - MO_U_Le _ | isComparisonExpr x -> Just $ CmmLit (CmmInt 1 (wordWidth dflags)) - MO_S_Le _ | isComparisonExpr x -> Just $ CmmLit (CmmInt 1 (wordWidth dflags)) - MO_U_Ge _ | isComparisonExpr x -> Just x + + -- Comparisons; trickier + -- See Note [Comparison operators] + MO_Ne _ | Just x' <- maybeInvertCmmExpr x -> Just x' -- (x>y) != 1 = x<=y + MO_Eq _ | isComparisonExpr x -> Just x -- (x>y) == 1 = x>y + MO_U_Lt _ | Just x' <- maybeInvertCmmExpr x -> Just x' -- (x>y) < 1 = x<=y + MO_S_Lt _ | Just x' <- maybeInvertCmmExpr x -> Just x' -- ditto + MO_U_Gt _ | isComparisonExpr x -> Just zero -- (x>y) > 1 = 0 + MO_S_Gt _ | isComparisonExpr x -> Just zero + MO_U_Le _ | isComparisonExpr x -> Just one -- (x>y) <= 1 = 1 + MO_S_Le _ | isComparisonExpr x -> Just one + MO_U_Ge _ | isComparisonExpr x -> Just x -- (x>y) >= 1 = x>y MO_S_Ge _ | isComparisonExpr x -> Just x _ -> Nothing + where + zero = CmmLit (CmmInt 0 (wordWidth dflags)) + one = CmmLit (CmmInt 1 (wordWidth dflags)) -- Now look for multiplication/division by powers of 2 (integers). @@ -376,6 +396,17 @@ cmmMachOpFoldM dflags mop [x, (CmmLit (CmmInt n _))] cmmMachOpFoldM _ _ _ = Nothing +{- Note [Comparison operators] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +If we have + CmmCondBranch ((x>#y) == 1) t f +we really want to convert to + CmmCondBranch (x>#y) t f + +That's what the constant-folding operations on comparison operators do above. +-} + + -- ----------------------------------------------------------------------------- -- Utils |