#15286: "Can't use Natural in base" when compiling GHC.Natural with -O0 -------------------------------------+------------------------------------- Reporter: alpmestan | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: | Version: 8.5 libraries/base | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Building GHC Unknown/Multiple | failed Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ _build/stage0/bin/ghc -Wall -hisuf hi -osuf o -hcsuf hc -static -hide-all- packages -no-user-package-db '-package-db _build/stage1/lib/package.conf.d' '-this-unit-id base-4.12.0.0' '-package- id ghc-prim-0.5.3' '-package-id integer-simple-0.1.1.1' '-package-id rts-1.0' -i -i_build/stage1/libraries/base/build -i_build/stage1/libraries/base/build/autogen -ilibraries/base/. -Iincludes -I_build/generated -I_build/stage1/libraries/base/build -I_build/stage1/libraries/base/build/include -Ilibraries/base/include -I/home/travis/build/snowleopard/hadrian/ghc/_build/stage1/lib/x86_64 -linux-ghc-8.5.20180617/rts-1.0/include -I_build/generated -optc- I_build/generated -optP-include -optP_build/stage1/libraries/base/build/autogen/cabal_macros.h -optc- std=gnu99 -optc-fno-stack-protector -optP-std=gnu99 -odir _build/stage1/libraries/base/build -hidir _build/stage1/libraries/base/build -stubdir _build/stage1/libraries/base/build -Wnoncanonical-monad-instances -optc- Werror=unused-but-set-variable -optc-Wno-error=inline -c libraries/base/GHC/Num.hs -o _build/stage1/libraries/base/build/GHC/Num.o -O0 -H64m -this-unit-id base -Wcompat -Wnoncanonical-monad-instances -XHaskell2010 -ghcversion- file=/home/travis/build/snowleopard/hadrian/ghc/_build/generated/ghcversion.h -Wno-deprecated-flags -Wno-trustworthy-safe Exit code: 1 Stderr: ghc: panic! (the 'impossible' happened) (GHC version 8.5.20180617 for x86_64-unknown-linux): Can't use Natural in base }}} We noticed this in hadrian land (in [https://github.com/snowleopard/hadrian/issues/499 this PR] and [https://github.com/snowleopard/hadrian/issues/629]), and noticed that this happens: - with 8.4.2 as the boot compiler but not 8.2.2 - with integer-simple as the integer library - only with the quickest flavour (or more generally when we build GHC.Natural with -O0) Some optimisation seems critical to making any trace of `Natural` disappear, but this seems rather fragile. The code that throws the error got introduced in fe770c211631e7b4c9b0b1e88ef9b6046c6585ef. The full build log is available [https://travis- ci.org/snowleopard/hadrian/jobs/393259151#L4209 here], anchored to where the error appears. An example of hadrian command to reproduce the problem, assuming a configured build tree: `hadrian/build.sh --flavour=quickest --integer- simple -j4`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15286 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler