recursion-ninja pushed to branch wip/fix-25664 at Glasgow Haskell Compiler / GHC Commits: e020f066 by Recursion Ninja at 2025-10-09T12:22:57-04:00 Changing manner in which truncation occur. - - - - - 1 changed file: - compiler/GHC/Cmm/Opt.hs Changes: ===================================== compiler/GHC/Cmm/Opt.hs ===================================== @@ -395,26 +395,28 @@ cmmMachOpFoldM platform mop [x, (CmmLit (CmmInt 1 rep))] one = CmmLit (CmmInt 1 (wordWidth platform)) -- Now look for multiplication/division by powers of 2 (integers). - -cmmMachOpFoldM platform mop [x, (CmmLit (CmmInt n w))] +-- +-- ToDo: See #25664 (comment 605821) describing a change to the Cmm literal representation. +-- When/If this is completed, this code must be refactored to account for the explicit width sizes. +cmmMachOpFoldM platform mop [x, (CmmLit (CmmInt n _))] = case mop of MO_Mul rep - | Just p <- widthBoundedExactLog2 False w n -> + | Just p <- exactLog2 (narrowU rep n) -> Just $! (cmmMachOpFold platform (MO_Shl rep) [x, CmmLit (CmmInt p $ wordWidth platform)]) MO_U_Quot rep - | Just p <- widthBoundedExactLog2 False w n -> + | Just p <- exactLog2 (narrowU rep n) -> Just $! (cmmMachOpFold platform (MO_U_Shr rep) [x, CmmLit (CmmInt p $ wordWidth platform)]) MO_U_Rem rep - | Just _ <- widthBoundedExactLog2 False w n -> + | Just _ <- exactLog2 (narrowU rep n) -> Just $! (cmmMachOpFold platform (MO_And rep) [x, CmmLit (CmmInt (n - 1) rep)]) MO_S_Quot rep - | Just p <- widthBoundedExactLog2 True w n, + | Just p <- exactLog2 (narrowS rep n), CmmReg _ <- x -> -- We duplicate x in signedQuotRemHelper, hence require -- it is a reg. FIXME: remove this restriction. Just $! (cmmMachOpFold platform (MO_S_Shr rep) [signedQuotRemHelper rep p, CmmLit (CmmInt p $ wordWidth platform)]) MO_S_Rem rep - | Just p <- widthBoundedExactLog2 True w n, + | Just p <- exactLog2 (narrowS rep n), CmmReg _ <- x -> -- We duplicate x in signedQuotRemHelper, hence require -- it is a reg. FIXME: remove this restriction. -- We replace (x `rem` 2^p) by (x - (x `quot` 2^p) * 2^p). @@ -449,14 +451,6 @@ cmmMachOpFoldM platform mop [x, (CmmLit (CmmInt n w))] x1 = CmmMachOp shr [x, CmmLit (CmmInt bits $ wordWidth platform)] x2 = if p == 1 then x1 else CmmMachOp (MO_And rep) [x1, CmmLit (CmmInt (n-1) rep)] - -- Determine if the input is an exact power of 2 AND within the logical range - -- of values permited by the bit-width. Without this check, the bit shifting - -- operations to multiply/divide by oowers of 2 may be unsound and result in - -- incorrect runtime results. - widthBoundedExactLog2 :: Bool -> Width -> Integer -> Maybe Integer - widthBoundedExactLog2 signed rep v = case exactLog2 v of - Just p | p >= fromIntegral (widthInBits rep - fromEnum signed) -> Nothing - m -> m -- ToDo (#7116): optimise floating-point multiplication, e.g. x*2.0 -> x+x -- Unfortunately this needs a unique supply because x might not be a View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/e020f06667f520353b367cc4882f1891... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/e020f06667f520353b367cc4882f1891... You're receiving this email because of your account on gitlab.haskell.org.