diff options
Diffstat (limited to 'compiler/codeGen/StgCmmExpr.hs')
| -rw-r--r-- | compiler/codeGen/StgCmmExpr.hs | 28 |
1 files changed, 24 insertions, 4 deletions
diff --git a/compiler/codeGen/StgCmmExpr.hs b/compiler/codeGen/StgCmmExpr.hs index 395e8d6fa6..3fbec6fcb7 100644 --- a/compiler/codeGen/StgCmmExpr.hs +++ b/compiler/codeGen/StgCmmExpr.hs @@ -304,6 +304,7 @@ cgCase (StgOpApp (StgPrimOp op) args _) bndr (AlgAlt tycon) alts ; (mb_deflt, branches) <- cgAlgAltRhss (NoGcInAlts,AssignedDirectly) (NonVoid bndr) alts + -- See Note [GC for conditionals] ; emitSwitch tag_expr branches mb_deflt 0 (tyConFamilySize tycon - 1) ; return AssignedDirectly } @@ -469,7 +470,8 @@ cgCase scrut bndr alt_type alts ; let ret_bndrs = chooseReturnBndrs bndr alt_type alts alt_regs = map (idToReg dflags) ret_bndrs ; simple_scrut <- isSimpleScrut scrut alt_type - ; let do_gc | not simple_scrut = True + ; let do_gc | is_cmp_op scrut = False -- See Note [GC for conditionals] + | not simple_scrut = True | isSingleton alts = False | up_hp_usg > 0 = False | otherwise = True @@ -484,11 +486,29 @@ cgCase scrut bndr alt_type alts ; _ <- bindArgsToRegs ret_bndrs ; cgAlts (gc_plan,ret_kind) (NonVoid bndr) alt_type alts } + where + is_cmp_op (StgOpApp (StgPrimOp op) _ _) = isComparisonPrimOp op + is_cmp_op _ = False + +{- Note [GC for conditionals] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +For boolean conditionals it seems that we have always done NoGcInAlts. +That is, we have always done the GC check before the conditional. +This is enshrined in the special case for + case tagToEnum# (a>b) of ... +See Note [case on bool] + +It's odd, and it's flagrantly inconsistent with the rules described +Note [Compiling case expressions]. However, after eliminating the +tagToEnum# (Trac #13397) we will have: + case (a>b) of ... +Rather than make it behave quite differently, I am testing for a +comparison operator here in in the general case as well. + +ToDo: figure out what the Right Rule should be. - -{- Note [scrut sequel] - +~~~~~~~~~~~~~~~~~~~ The job of the scrutinee is to assign its value(s) to alt_regs. Additionally, if we plan to do a heap-check in the alternatives (see Note [Compiling case expressions]), then we *must* retreat Hp to |