diff options
Diffstat (limited to 'compiler/codeGen')
| -rw-r--r-- | compiler/codeGen/StgCmmExpr.hs | 20 |
1 files changed, 14 insertions, 6 deletions
diff --git a/compiler/codeGen/StgCmmExpr.hs b/compiler/codeGen/StgCmmExpr.hs index 2f2cdbba14..51578b1cc4 100644 --- a/compiler/codeGen/StgCmmExpr.hs +++ b/compiler/codeGen/StgCmmExpr.hs @@ -432,18 +432,26 @@ cgCase scrut bndr alt_type alts ; mb_cc <- maybeSaveCostCentre simple_scrut - -- if do_gc then our sequel will be ReturnTo - -- - generate code for the sequel now - -- - pass info about the sequel to cgAlts for use in the heap check - -- else sequel will be AssignTo - - ; ret_kind <- withSequel (AssignTo alt_regs False) (cgExpr scrut) + ; let sequel = AssignTo alt_regs do_gc{- Note [scrut sequel] -} + ; ret_kind <- withSequel sequel (cgExpr scrut) ; restoreCurrentCostCentre mb_cc ; _ <- bindArgsToRegs ret_bndrs ; cgAlts (gc_plan,ret_kind) (NonVoid bndr) alt_type alts } +{- +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 +recover any unused heap before passing control to the sequel. If we +don't do this, then any unused heap will become slop because the heap +check will reset the heap usage. Slop in the heap breaks LDV profiling +(+RTS -hb) which needs to do a linear sweep through the nursery. +-} + ----------------- maybeSaveCostCentre :: Bool -> FCode (Maybe LocalReg) maybeSaveCostCentre simple_scrut |