[Git][ghc/ghc][wip/marge_bot_batch_merge_job] 7 commits: Implement -Wredundant-bang-patterns (#17340)

[Marge Bot]

 Marge Bot pushed to branch wip/marge_bot_batch_merge_job at Glasgow Haskell Compiler / GHC


Commits:
731c8d3b by nineonine at 2020-08-19T18:47:39-04:00
Implement -Wredundant-bang-patterns (#17340)

Add new flag '-Wredundant-bang-patterns' that enables checks for "dead" bangs.
Dead bangs are the ones that under no circumstances can force a thunk that
wasn't already forced. Dead bangs are a form of redundant bangs. The new check
is performed in Pattern-Match Coverage Checker along with other checks (namely,
redundant and inaccessible RHSs). Given

    f :: Bool -> Int
    f True = 1
    f !x   = 2

we can detect dead bang patterns by checking whether @x ~ ⊥@ is satisfiable
where the PmBang appears in 'checkGrdTree'. If not, then clearly the bang is
dead. Such a dead bang is then indicated in the annotated pattern-match tree by
a 'RedundantSrcBang' wrapping. In 'redundantAndInaccessibles', we collect
all dead bangs to warn about.

Note that we don't want to warn for a dead bang that appears on a redundant
clause. That is because in that case, we recommend to delete the clause wholly,
including its leading pattern match.

Dead bang patterns are redundant. But there are bang patterns which are
redundant that aren't dead, for example

    f !() = 0

the bang still forces the match variable, before we attempt to match on (). But
it is redundant with the forcing done by the () match. We currently don't
detect redundant bangs that aren't dead.

- - - - -
eb9bdaef by Simon Peyton Jones at 2020-08-19T18:48:14-04:00
Add right-to-left rule for pattern bindings

Fix #18323 by adding a few lines of code to handle non-recursive
pattern bindings.  see GHC.Tc.Gen.Bind
Note [Special case for non-recursive pattern bindings]

Alas, this confused the pattern-match overlap checker; see #18323.

Note that this patch only affects pattern bindings like that
for (x,y) in this program

  combine :: (forall a . [a] -> a) -> [forall a. a -> a]
          -> ((forall a . [a] -> a), [forall a. a -> a])

  breaks = let (x,y) = combine head ids
           in x y True

We need ImpredicativeTypes for those [forall a. a->a] types to be
valid. And with ImpredicativeTypes the old, unprincipled "allow
unification variables to unify with a polytype" story actually
works quite well. So this test compiles fine (if delicatedly) with
old GHCs; but not with QuickLook unless we add this patch

- - - - -
de201efc by Sylvain Henry at 2020-08-21T02:56:25-04:00
Put CFG weights into their own module (#17957)

It avoids having to query DynFlags to get them

- - - - -
b3ca4d70 by Sylvain Henry at 2020-08-21T02:56:25-04:00
Don't use DynFlags in CmmToAsm.BlockLayout (#17957)

- - - - -
0f17d2a2 by Sylvain Henry at 2020-08-21T02:56:25-04:00
NCG: Dwarf configuration

* remove references to DynFlags in GHC.CmmToAsm.Dwarf
* add specific Dwarf options in NCGConfig instead of directly querying
  the debug level

- - - - -
1c0bf320 by Sylvain Henry at 2020-08-21T02:56:26-04:00
Fix -ddump-stg flag

-ddump-stg was dumping the initial STG (just after Core-to-STG pass)
which was misleading because we want the final STG to know if a function
allocates or not. Now we have a new flag -ddump-stg-from-core for this and
-ddump-stg is deprecated.

- - - - -
2773b144 by Vladislav Zavialov at 2020-08-21T02:56:27-04:00
Import qualified Prelude in Cmm/Parser.y

In preparation for the next version of 'happy', c95920 added a qualified
import to GHC/Parser.y but for some reason neglected GHC/Cmm/Parser.y

This patch adds the missing qualified import to GHC/Cmm/Parser.y and
also adds a clarifying comment to explain why this import is needed.

- - - - -


30 changed files:

- compiler/GHC/Cmm/Info/Build.hs
- compiler/GHC/Cmm/Parser.y
- compiler/GHC/CmmToAsm.hs
- compiler/GHC/CmmToAsm/BlockLayout.hs
- compiler/GHC/CmmToAsm/CFG.hs
- + compiler/GHC/CmmToAsm/CFG/Weight.hs
- compiler/GHC/CmmToAsm/Config.hs
- compiler/GHC/CmmToAsm/Dwarf.hs
- compiler/GHC/CmmToAsm/Monad.hs
- compiler/GHC/CmmToAsm/PPC/Ppr.hs
- compiler/GHC/CmmToAsm/X86/CodeGen.hs
- compiler/GHC/CmmToAsm/X86/Ppr.hs
- compiler/GHC/CmmToLlvm/Base.hs
- compiler/GHC/CmmToLlvm/CodeGen.hs
- compiler/GHC/Driver/Backpack.hs
- compiler/GHC/Driver/Flags.hs
- compiler/GHC/Driver/Ppr.hs
- compiler/GHC/Driver/Session.hs
- compiler/GHC/Hs/Binds.hs
- compiler/GHC/Hs/Utils.hs
- compiler/GHC/HsToCore/Binds.hs
- compiler/GHC/HsToCore/Expr.hs
- compiler/GHC/HsToCore/PmCheck.hs
- compiler/GHC/Parser.y
- compiler/GHC/Stg/Pipeline.hs
- compiler/GHC/Tc/Gen/Bind.hs
- compiler/GHC/Tc/Gen/Match.hs
- compiler/GHC/Tc/Gen/Match.hs-boot
- compiler/GHC/Tc/Utils/Zonk.hs
- compiler/GHC/Unit/State.hs


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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/74e57004c54728ad9e9f1e6af8ebb92365e8ed95...2773b14489540e729bc6fe1744dc6f817ec1a559

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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/74e57004c54728ad9e9f1e6af8ebb92365e8ed95...2773b14489540e729bc6fe1744dc6f817ec1a559
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