Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC

Commits:

• 4bfbf5c8
  by ARATA Mizuki at 2026-09-01T18:55:08-04:00

  testsuite: Fix out-of-bounds access in T3586
  
  unsafeRead and unsafeWrite use 0-based index.
  
  Looking at #3586, the expected output seems to be 2.8e8.
  
  Addresses #27596
  

• 3f9db6d4
  by ARATA Mizuki at 2026-09-01T18:55:08-04:00

  testsuite: Fix out-of-bounds access in T21305
  
  writeInt64Array# takes an index measured in units of Int64 elements.
  
  Fixes #27596
  

3 changed files:

• testsuite/tests/ffi/should_run/T21305.hs
• testsuite/tests/perf/should_run/T3586.hs
• testsuite/tests/perf/should_run/T3586.stdout

Changes:

 writeByteArray# _   _   []          s = s

 writeByteArray# mba off (I64# i:is) s =

   case writeInt64Array# mba off i s of

-    s' -> writeByteArray# mba (off +# 8#) is s'

+    s' -> writeByteArray# mba (off +# 1#) is s'

 go !a i !acc

     | i < 1     = return acc

     | otherwise = do

-         b <- unsafeRead a i

-         unsafeWrite a i (b+3.0)

-         c <- unsafeRead a i

+         -- unsafeRead/unsafeWrite use 0-based index

+         b <- unsafeRead a (i-1)

+         unsafeWrite a (i-1) (b+3.0)

+         c <- unsafeRead a (i-1)

          go a (i-1) (c+acc)

-2.79999863e8

+2.8e8