HEAD panics with toIfaceCoercionX when dumping core.
I added dump flags to a file on head:
diff --git a/compiler/GHC/Tc/Gen/Head.hs b/compiler/GHC/Tc/Gen/Head.hs
index feb984fc26..7e227653d0 100644
--- a/compiler/GHC/Tc/Gen/Head.hs
+++ b/compiler/GHC/Tc/Gen/Head.hs
@@ -8,7 +8,7 @@
{-# LANGUAGE UndecidableInstances #-} -- Wrinkle in Note [Trees That Grow]
{-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}
-
+{-# OPTIONS_GHC -ddump-simpl -ddump-to-file -dverbose-core2core -ddump-stg-final #-}
{-
%
(c) The University of Glasgow 2006
I then tried to build the compiler but I get:
hadrian/build -j14 --flavour=default+no_profiled_libs -o_build2
...
!!! CoreTidy [GHC.Tc.Gen.Head]: finished in 375.00 milliseconds, allocated 510.122 megabytes
*** CorePrep [GHC.Tc.Gen.Head]:
ghc.exe: panic! (the 'impossible' happened)
(GHC version 9.3.20210428:
toIfaceCoercionX
Call stack:
CallStack (from HasCallStack):
callStackDoc, called at compiler\\GHC\\Utils\\Panic.hs:181:37 in ghc:GHC.Utils.Panic
pprPanic, called at compiler\\GHC\\CoreToIface.hs:316:35 in ghc:GHC.CoreToIface
Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug
This is likely caused by this commit as it introduced the panic: