id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
2011	[6.8.1 regression] panic: lookupVers1 base:GHC.Prim sym{tc}	simonmar	igloo	"When rebuilding the base package you might encounter this:

{{{
../../compiler/stage1/ghc-inplace -package-name base-3.0.1.0 -hide-all-packages -split-objs -i -idist/build/autogen -idist/build -i. -Idist/build -Iinclude -#include ""HsBase.h"" -odir dist/build -hidir dist/build -stubdir dist/build -package rts-1.0 -O -fglasgow-exts -package-name base -XCPP -idist/build  -H16m -O -O -Rghc-timing -fgenerics -c Data/Generics/Twins.hs -o dist/build/Data/Generics/Twins.o  -ohi dist/build/Data/Generics/Twins.hi
ghc-6.8.2: panic! (the 'impossible' happened)
  (GHC version 6.8.2 for powerpc-apple-darwin):
        lookupVers1 base:GHC.Prim sym{tc}
}}}

Workaround is to clean in `libraries/base`.

The problem is that `MkIface.computeChangedOccs` needs to avoid wired-in names when checking version numbers, because wired-in names are never mentioned in usages.

I believe simonpj has a patch for this in his working tree, we diagnosed it before disappearing for the Christmas period."	merge	closed	high	6.8.3	Compiler	6.8.2	fixed			Unknown/Multiple	Unknown/Multiple		Unknown