#13410: GHC HEAD regression: Template variable unbound in rewrite rule -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.2.1 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by RyanGlScott: Old description:
`hybrid-vectors-0.2.1` currently fails to build with GHC HEAD. I've attached a minimized repro file with no dependencies (it's 410 lines long, since I had to copy-paste a lot of code from `vector` in order to reproduce this). The attached file builds on GHC 7.10.3 and 8.0.2, but fails on GHC HEAD with this panic:
{{{ $ ~/Software/ghc2/inplace/bin/ghc-stage2 -O2 -fforce-recomp Bug.hs [1 of 1] Compiling Data.Vector.Hybrid.Internal ( Bug.hs, Bug.o )
Bug.hs:389:10: warning: [-Wmissing-methods] • No explicit implementation for ‘gmbasicOverlaps’, ‘gmbasicInitialize’, and ‘gmbasicUnsafeRead’ • In the instance declaration for ‘GMVector (MVector u v) (a, b)’ | 389 | instance (GMVector u a, GMVector v b) => GMVector (MVector u v) (a, b) where | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Bug.hs:407:10: warning: [-Wmissing-methods] • No explicit implementation for ‘gbasicUnsafeFreeze’, ‘gbasicUnsafeThaw’, ‘gbasicLength’, ‘gbasicUnsafeSlice’, and ‘gbasicUnsafeIndexM’ • In the instance declaration for ‘GVector (Vector u v) (a, b)’ | 407 | instance (GVector u a, GVector v b) => GVector (Vector u v) (a, b) where | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.3.20170310 for x86_64-unknown-linux): Template variable unbound in rewrite rule Variable: sc_s8FV Rule "SC:$j0" Rule bndrs: [sc_s8FV, sc_s8FW, sc_s8FX, sg_s8FY, sc_s8FU] LHS args: [sc_s8FU, (MV @ (GMutable u_a4oM) @ (GMutable v_a4oO) @ (PrimState (ST RealWorld)) @ (a_a4oN, b_a4oP) @ a_a4oN @ b_a4oP @~ (<(a_a4oN, b_a4oP)>_N :: ((a_a4oN, b_a4oP) :: *) ~# ((a_a4oN, b_a4oP) :: *)) sc_s8FW sc_s8FX) `cast` (sg_s8FY :: (MVector (GMutable u_a4oM) (GMutable v_a4oO) (PrimState (ST RealWorld)) (a_a4oN, b_a4oP) :: *) ~R# (GMutable (Vector u_a4oM v_a4oO) (PrimState (ST RealWorld)) c_a4oQ :: *))] Actual args: [sc_s8FS, wild_X3x `cast` (Sub (Sym (D:R:GMutableVector[0]
_N _N)) _N (Sym cobox_a4Gz) :: (MVector (GMutable u_a4oM) (GMutable v_a4oO) (PrimState (ST RealWorld)) (a_a4oN, b_a4oP) :: *) ~R# (GMutable (Vector u_a4oM v_a4oO) (PrimState (ST RealWorld)) c_a4oQ :: *))] Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1191:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1195:37 in ghc:Outputable pprPanic, called at compiler/specialise/Rules.hs:579:19 in ghc:Rules }}} Some important things to note:
* `-O2` is required to trigger this bug; using `-O1` or below works fine. * The problematic code is the `Read (Vector u v c)` instance at the very bottom. In particular, commenting out the last line `readPrec = greadPrec` makes the panic go away. * Moreover, there's a particular `INLINE` pragma in the `GMVector (MVector u v) (a, b)` instance that is critical to triggering the panic (it's on line 394; I've added a comment `Removing this INLINE pragma makes it compile` above it).
New description:
`hybrid-vectors-0.2.1` currently fails to build with GHC HEAD. I've
attached a minimized repro file with no dependencies (it's 410 lines long,
since I had to copy-paste a lot of code from `vector` in order to
reproduce this). The attached file builds on GHC 7.10.3 and 8.0.2, but
fails on GHC HEAD with this panic:
{{{
$ ~/Software/ghc2/inplace/bin/ghc-stage2 -O2 -fforce-recomp Bug.hs
[1 of 1] Compiling Data.Vector.Hybrid.Internal ( Bug.hs, Bug.o )
Bug.hs:389:10: warning: [-Wmissing-methods]
• No explicit implementation for
‘gmbasicOverlaps’, ‘gmbasicInitialize’, and ‘gmbasicUnsafeRead’
• In the instance declaration for ‘GMVector (MVector u v) (a, b)’
|
389 | instance (GMVector u a, GMVector v b) => GMVector (MVector u v) (a,
b) where
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Bug.hs:407:10: warning: [-Wmissing-methods]
• No explicit implementation for
‘gbasicUnsafeFreeze’, ‘gbasicUnsafeThaw’, ‘gbasicLength’,
‘gbasicUnsafeSlice’, and ‘gbasicUnsafeIndexM’
• In the instance declaration for ‘GVector (Vector u v) (a, b)’
|
407 | instance (GVector u a, GVector v b) => GVector (Vector u v) (a, b)
where
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ghc-stage2: panic! (the 'impossible' happened)
(GHC version 8.3.20170310 for x86_64-unknown-linux):
Template variable unbound in rewrite rule
Variable: sc_s8FV
Rule "SC:$j0"
Rule bndrs: [sc_s8FV, sc_s8FW, sc_s8FX, sg_s8FY, sc_s8FU]
LHS args: [sc_s8FU,
(MV
@ (GMutable u_a4oM)
@ (GMutable v_a4oO)
@ (PrimState (ST RealWorld))
@ (a_a4oN, b_a4oP)
@ a_a4oN
@ b_a4oP
@~ (<(a_a4oN, b_a4oP)>_N
:: ((a_a4oN, b_a4oP) :: *) ~# ((a_a4oN, b_a4oP) :: *))
sc_s8FW
sc_s8FX)
`cast` (sg_s8FY
:: (MVector
(GMutable u_a4oM)
(GMutable v_a4oO)
(PrimState (ST RealWorld))
(a_a4oN, b_a4oP) :: *)
~R#
(GMutable
(Vector u_a4oM v_a4oO) (PrimState (ST
RealWorld)) c_a4oQ :: *))]
Actual args: [sc_s8FS,
wild_X3x
`cast` (Sub
(Sym (D:R:GMutableVector[0]