Simon Jakobi pushed to branch wip/sjakobi/mr16259 at Glasgow Haskell Compiler / GHC

Commits:

• 201c4864
  by Simon Jakobi at 2026-07-11T09:00:05+02:00

  wasm: untag the Weak# obtained through a StablePtr in rts_promiseThrowTo
  
  Same defect class as the hs_try_putmvar fixes: the Weak# created around
  a JSFFI export's TSO now carries tag 1 (#23173) and makeStablePtr#
  stores it tagged, so rts_promiseThrowTo read all StgWeak fields one
  byte off and crashed in throwToMsg (jsffi/cancel in the second CI run
  of !16329). The resolve/reject paths were already covered by the
  hs_try_putmvar_with_value fix.
  
  Assisted-by: Claude Fable 5
  

• 4dde58bb
  by Simon Jakobi at 2026-07-11T09:00:05+02:00

  Accept remaining compile-time metric increases from enter-taggable enforcement
  
  Second CI run of !16329 flagged three more compile-time allocation
  increases beyond T13960: T20049 (+2.0%, right at the window edge, on
  x86_64 validate jobs) and, on the wasm cross job only, T6048 (+2.2%)
  and T16577 (+5.7%). These are the emitEnter tag-test cost of the
  invariant enforcement (#23173); the wasm numbers suggest the cost is
  higher without TablesNextToCode.
  
  The perf driver reads the Metric Increase block from the HEAD commit
  only, hence this empty commit at the branch tip; it supersedes the
  earlier one for T13960.
  
  -------------------------
  Metric Increase:
      T13960
      T16577
      T20049
      T6048
  -------------------------
  
  Assisted-by: Claude Fable 5
  

1 changed file:

• rts/wasm/JSFFI.c

Changes:

 void rts_promiseThrowTo(HsStablePtr, HsJSVal);

 void rts_promiseThrowTo(HsStablePtr sp, HsJSVal js_err) {

   Capability *cap = &MainCapability;

-  StgWeak *w = (StgWeak *)deRefStablePtr(sp);

+  // Weak# pointers carry tag 1; see Note [Pointer tagging of unlifted boxed

+  // primitives] in GHC.StgToCmm.Prim. (The key field is stored untagged.)

+  StgWeak *w = (StgWeak *)UNTAG_CLOSURE((StgClosure *)deRefStablePtr(sp));

   if (w->header.info == &stg_DEAD_WEAK_info) {

     return;

   }