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| author | Ben Gamari <ben@smart-cactus.org> | 2021-11-07 00:31:04 -0400 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2022-03-02 09:00:44 -0500 |
| commit | 4ddc62e55fa1eddaa98d54df54b3be1b1759a1e7 (patch) | |
| tree | 8237bf179b250ac6b5b6d0cb9097642d0e164ee1 | |
| parent | 7896cd36e4036648aa59c2b942eea4653466350b (diff) | |
| download | haskell-4ddc62e55fa1eddaa98d54df54b3be1b1759a1e7.tar.gz | |
cmm: narrow when folding signed quotients
Previously the constant-folding behavior for MO_S_Quot and MO_S_Rem
failed to narrow its arguments, meaning that a program like:
%zx64(%quot(%lobits8(0x00e1::bits16), 3::bits8))
would be miscompiled. Specifically, this program should reduce as
%lobits8(0x00e1::bits16) == -31
%quot(%lobits8(0x00e1::bits16), 3::bits8) == -10
%zx64(%quot(%lobits8(0x00e1::bits16), 3::bits8)) == 246
However, with this bug the `%lobits8(0x00e1::bits16)` would instead
be treated as `+31`, resulting in the incorrect result of `75`.
(cherry picked from commit 94e197e3dbb9a48991eb90a03b51ea13d39ba4cc)
(cherry picked from commit 5b950a7f939a35538abf61ea8e86ddd07cc75237)
| -rw-r--r-- | compiler/GHC/Cmm/Opt.hs | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/compiler/GHC/Cmm/Opt.hs b/compiler/GHC/Cmm/Opt.hs index 6a2945c4f8..dc81a2c7aa 100644 --- a/compiler/GHC/Cmm/Opt.hs +++ b/compiler/GHC/Cmm/Opt.hs @@ -134,8 +134,8 @@ cmmMachOpFoldM platform mop [CmmLit (CmmInt x xrep), CmmLit (CmmInt y _)] MO_Mul r -> Just $! CmmLit (CmmInt (x * y) r) MO_U_Quot r | y /= 0 -> Just $! CmmLit (CmmInt (x_u `quot` y_u) r) MO_U_Rem r | y /= 0 -> Just $! CmmLit (CmmInt (x_u `rem` y_u) r) - MO_S_Quot r | y /= 0 -> Just $! CmmLit (CmmInt (x `quot` y) r) - MO_S_Rem r | y /= 0 -> Just $! CmmLit (CmmInt (x `rem` y) r) + MO_S_Quot r | y /= 0 -> Just $! CmmLit (CmmInt (x_s `quot` y_s) r) + MO_S_Rem r | y /= 0 -> Just $! CmmLit (CmmInt (x_s `rem` y_s) r) MO_And r -> Just $! CmmLit (CmmInt (x .&. y) r) MO_Or r -> Just $! CmmLit (CmmInt (x .|. y) r) |