## Summary GHC 9.4.5 panics with lookupIdSubst when building a benchmark of my library. ``` [2 of 3] Compiling IGA ( benchmark/IGA.hs, /tmp/haskell-floating-point/dist-newstyle/build/x86_64-linux/ghc-9.4.5/rounded-hw-0.3.0/build/rounded-hw-benchmark/rounded-hw-benchmark-tmp/IGA.o ) <no location info>: error: panic! (the 'impossible' happened) GHC version 9.4.5: lookupIdSubst df_sfFs InScope {$dUnbox_X0 $dIArray_Xf $dFractional_Xg $dIArray_adxd df_adxe $dUnbox_adxf $dFractional_adxs $dIArray_adxt df_adxu $dUnbox_adxv $sintervalGaussianEliminationU_ddPi $sintervalGaussianEliminationU_ddPj $sintervalGaussianEliminationU_ddPk intervalGaussianElimination intervalGaussianEliminationU benchmark $trModule $trModule_seOB $trModule_seOC $trModule_seOD $trModule_seOE loc_seOF loc_seOG loc_seOH loc_seOI loc_seOJ loc_seOK loc_seOL $dIP_seOM $dIP_seON $dIP_seOO loc_seRU loc_seRV loc_seRW loc_seRX loc_seRY loc_seRZ loc_seS0 $dIP_seS1 $dIP_seS2 $dIP_seS3 loc_seZA loc_seZB loc_seZC loc_seZD loc_seZE loc_seZF loc_seZG $dIP_seZH $dIP_seZI $dIP_seZJ benchmark_sfzR benchmark_sfzS} Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/GHC/Utils/Panic.hs:182:37 in ghc:GHC.Utils.Panic pprPanic, called at compiler/GHC/Core/Subst.hs:260:17 in ghc:GHC.Core.Subst Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug Error: cabal: Failed to build rounded-hw-0.3.0. ``` ## Steps to reproduce ``` $ git clone https://github.com/minoki/haskell-floating-point.git $ cd haskell-floating-point/ $ cabal build -w ghc-9.4.5 --enable-benchmarks rounded-hw ``` ## Expected behavior The benchmark should build fine. ## Environment * GHC version used: 9.4.5 The GHC built from https://gitlab.haskell.org/ghc/ghc/-/commits/wip/9.4.6-backports/ is also affected, so this is a different issue from #22761. Other series (9.2.x, 9.6.x, 9.8.1-alpha1) are not affected. Optional: * Operating System: x86\_64 and AArch64 * System Architecture: Linux and macOS