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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2019-08-30 13:43:24 +0100 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2019-09-20 10:50:21 +0100 |
| commit | 0dad81ca5fd1f63bf8a3b6ad09787559e8bd05c0 (patch) | |
| tree | 8759889c9a5bfe5f59dda0f809c2bfc1b8fab3f1 /compiler/simplCore/SimplUtils.hs | |
| parent | 1755424806839d57a0c5672922a4b65b838f7d17 (diff) | |
| download | haskell-0dad81ca5fd1f63bf8a3b6ad09787559e8bd05c0.tar.gz | |
Fix bogus type of case expressionwip/T17056
Issue #17056 revealed that we were sometimes building a case
expression whose type field (in the Case constructor) was bogus.
Consider a phantom type synonym
type S a = Int
and we want to form the case expression
case x of K (a::*) -> (e :: S a)
We must not make the type field of the Case constructor be (S a)
because 'a' isn't in scope. We must instead expand the synonym.
Changes in this patch:
* Expand synonyms in the new function CoreUtils.mkSingleAltCase.
* Use mkSingleAltCase in MkCore.wrapFloat, which was the proximate
source of the bug (when called by exprIsConApp_maybe)
* Use mkSingleAltCase elsewhere
* Documentation
CoreSyn new invariant (6) in Note [Case expression invariants]
CoreSyn Note [Why does Case have a 'Type' field?]
CoreUtils Note [Care with the type of a case expression]
* I improved Core Lint's error reporting, which was pretty
confusing in this case, because it didn't mention that the offending
type was the return type of a case expression.
* A little bit of cosmetic refactoring in CoreUtils
Diffstat (limited to 'compiler/simplCore/SimplUtils.hs')
| -rw-r--r-- | compiler/simplCore/SimplUtils.hs | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/compiler/simplCore/SimplUtils.hs b/compiler/simplCore/SimplUtils.hs index 63c216fce2..4eeb51ceaa 100644 --- a/compiler/simplCore/SimplUtils.hs +++ b/compiler/simplCore/SimplUtils.hs @@ -2212,8 +2212,10 @@ mkCase2 dflags scrut bndr alts_ty alts ; return (ex_tvs ++ arg_ids) } mk_new_bndrs _ _ = return [] - re_sort :: [CoreAlt] -> [CoreAlt] -- Re-sort the alternatives to - re_sort alts = sortBy cmpAlt alts -- preserve the #case_invariants# + re_sort :: [CoreAlt] -> [CoreAlt] + -- Sort the alternatives to re-establish + -- CoreSyn Note [Case expression invariants] + re_sort alts = sortBy cmpAlt alts add_default :: [CoreAlt] -> [CoreAlt] -- See Note [Literal cases] |