[GHC] #15570: Core transformations generate bad indexCharOffAddr# call

[GHC]

#15570: Core transformations generate bad indexCharOffAddr# call
-------------------------------------+-------------------------------------
        Reporter:  alpmestan         |                Owner:  alpmestan
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.5
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 OK, with some help from Andrey I added to `hadrian/src/UserSettings.hs`
 {{{
 verboseCommand :: Predicate
 verboseCommand = input "//*.hs"
 }}}
 Now if I touch `GHC/Real.hs` I get its command line, which is super-
 helpful; so I can compile with changing flags.

 Turns out that the reason for the strange `GHC.Real.even3` is that we have
 {{{
 GHC.Real.even4 :: Int
 GHC.Real.even4 = GHC.Types.I# 1#

 -- RHS size: {terms: 3, types: 1, coercions: 0, joins: 0/0}
 GHC.Real.even3 :: Int
 GHC.Real.even3 = negate @ Int GHC.Num.$fNumInt GHC.Real.even4
 }}}
 Wny aren't we negating that constant?  '''Turns out that it's because we
 aren't optimising `GHC.Num`'''!!! It's not surprising that we get terrible
 code.

 Here are the command lines printed by Hadrian for `GHC.Num` and `GHC.Real`
 {{{
 -- GHC.Real.  Notice that it finishes with -O
 _build/stage0/bin/ghc -Wall -hisuf dyn_hi -osuf dyn_o -hcsuf dyn_hc -fPIC
 -dynamic -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-gmp-1.0.2.0' '-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/simonpj/code/HEAD-3/_build/stage1/lib/x86_64-linux-
 ghc-8.7.20180825/integer-gmp-1.0.2.0/include
 -I/home/simonpj/code/HEAD-3/_build/stage1/lib/x86_64-linux-
 ghc-8.7.20180825/rts-1.0/include -I_build/generated -optc-
 I_build/generated -optP-include
 -optP_build/stage1/libraries/base/build/autogen/cabal_macros.h -optc-fno-
 stack-protector -optP-DOPTIMISE_INTEGER_GCD_LCM -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/Real.hs -o
 _build/stage1/libraries/base/build/GHC/Real.dyn_o -O0 -H64m -this-unit-id
 base -Wcompat -Wnoncanonical-monad-instances -XHaskell2010 -ghcversion-
 file=/home/simonpj/code/HEAD-3/_build/generated/ghcversion.h -O -Wno-
 deprecated-flags -Wno-trustworthy-safe

 -- GHC.Num. The -O is there but it's overridden with -O0
 _build/stage0/bin/ghc -Wall -hisuf dyn_hi -osuf dyn_o -hcsuf dyn_hc -fPIC
 -dynamic -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-gmp-1.0.2.0' '-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/simonpj/code/HEAD-3/_build/stage1/lib/x86_64-linux-
 ghc-8.7.20180825/integer-gmp-1.0.2.0/include
 -I/home/simonpj/code/HEAD-3/_build/stage1/lib/x86_64-linux-
 ghc-8.7.20180825/rts-1.0/include -I_build/generated -optc-
 I_build/generated -optP-include
 -optP_build/stage1/libraries/base/build/autogen/cabal_macros.h -optc-fno-
 stack-protector -optP-DOPTIMISE_INTEGER_GCD_LCM -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.dyn_o -O0 -H64m -this-unit-id
 base -Wcompat -Wnoncanonical-monad-instances -XHaskell2010 -ghcversion-
 file=/home/simonpj/code/HEAD-3/_build/generated/ghcversion.h -O -O0 -fno-
 ignore-interface-pragmas -Wno-deprecated-flags -Wno-trustworthy-safe
 }}}
 Blimey. With `make` we'd be stuck: who is adding that `-O0`?  But with
 Hadrian and it's provenance tracking, it should be easy.

 But I have no idea where to start: Andrey, Alp, over to you.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15570#comment:10>
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