Commit 89597d21 authored by Simon Marlow's avatar Simon Marlow

Fix #3132: a case of bogus code generation

parent 65064489
......@@ -37,9 +37,12 @@ import ForeignCall
import VarSet
import CoreSyn
import PrimOp
import Type
import TyCon
import Util
import Outputable
import Control.Monad (when)
\end{code}
\begin{code}
......@@ -120,15 +123,38 @@ eliminate a heap check altogether.
\begin{code}
cgCase (StgApp v []) _live_in_whole_case _live_in_alts bndr
alt_type@(PrimAlt _) alts
= do { -- Careful! we can't just bind the default binder to the same thing
-- Note [ticket #3132]: we might be looking at a case of a lifted Id
-- that was cast to an unlifted type. The Id will always be bottom,
-- but we don't want the code generator to fall over here. If we
-- just emit an assignment here, the assignment will be
-- type-incorrect Cmm. Hence we check that the types match, and if
-- they don't we'll fall through and emit the usual enter/return
-- code. Test case: codeGen/should_compile/3132.hs
| isUnLiftedType (idType v)
-- However, we also want to allow an assignment to be generated
-- in the case when the types are compatible, because this allows
-- some slightly-dodgy but occasionally-useful casts to be used,
-- such as in RtClosureInspect where we cast an HValue to a MutVar#
-- so we can print out the contents of the MutVar#. If we generate
-- code that enters the HValue, then we'll get a runtime panic, because
-- the HValue really is a MutVar#. The types are compatible though,
-- so we can just generate an assignment.
|| reps_compatible
=
do { -- Careful! we can't just bind the default binder to the same thing
-- as the scrutinee, since it might be a stack location, and having
-- two bindings pointing at the same stack locn doesn't work (it
-- confuses nukeDeadBindings). Hence, use a new temp.
v_info <- getCgIdInfo v
when (not reps_compatible) $
panic "cgCase: reps do not match, perhaps a dodgy unsafeCoerce?"
; v_info <- getCgIdInfo v
; amode <- idInfoToAmode v_info
; tmp_reg <- bindNewToTemp bndr
; stmtC (CmmAssign (CmmLocal tmp_reg) amode)
; cgPrimAlts NoGC alt_type (CmmLocal tmp_reg) alts }
where
reps_compatible = idCgRep v == idCgRep bndr
\end{code}
Special case #3: inline PrimOps and foreign calls.
......
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