Commit 48845462 authored by gmainlan@microsoft.com's avatar gmainlan@microsoft.com
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Allow case expressions with a single alternative to be floated in.

This change generalizes support for floating in case expressions. Previously,
case expression with an unlifted scrutinee and a single DEFAULT alternative were
floated in. In particular, this allowed array index operations to be floated
in. We also want to float in SIMD unpack primops, which return an unboxed tuple
of scalars, thus the generalization.
parent 000d4517
......@@ -354,19 +354,27 @@ For @Case@, the possible ``drop points'' for the \tr{to_drop}
bindings are: (a)~inside the scrutinee, (b)~inside one of the
alternatives/default [default FVs always {\em first}!].
Floating case expressions inward was added to fix Trac #5658: strict bindings
not floated in. In particular, this change allows array indexing operations,
which have a single DEFAULT alternative without any binders, to be floated
inward. SIMD primops for unpacking SIMD vectors into an unboxed tuple of unboxed
scalars also need to be floated inward, but unpacks have a single non-DEFAULT
alternative that binds the elements of the tuple. We now therefore also support
floating in cases with a single alternative that may bind values.
\begin{code}
fiExpr to_drop (_, AnnCase scrut case_bndr _ [(DEFAULT,[],rhs)])
fiExpr to_drop (_, AnnCase scrut case_bndr _ [(con,alt_bndrs,rhs)])
| isUnLiftedType (idType case_bndr)
, exprOkForSideEffects (deAnnotate scrut)
= wrapFloats shared_binds $
fiExpr (case_float : rhs_binds) rhs
where
case_float = FB (unitVarSet case_bndr) scrut_fvs
(FloatCase scrut' case_bndr DEFAULT [])
case_float = FB (mkVarSet (case_bndr : alt_bndrs)) scrut_fvs
(FloatCase scrut' case_bndr con alt_bndrs)
scrut' = fiExpr scrut_binds scrut
[shared_binds, scrut_binds, rhs_binds]
= sepBindsByDropPoint False [freeVarsOf scrut, rhs_fvs] to_drop
rhs_fvs = freeVarsOf rhs `delVarSet` case_bndr
rhs_fvs = freeVarsOf rhs `delVarSetList` (case_bndr : alt_bndrs)
scrut_fvs = freeVarsOf scrut
fiExpr to_drop (_, AnnCase scrut case_bndr ty alts)
......
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