diff options
Diffstat (limited to 'compiler/simplCore/FloatOut.hs')
| -rw-r--r-- | compiler/simplCore/FloatOut.hs | 27 |
1 files changed, 13 insertions, 14 deletions
diff --git a/compiler/simplCore/FloatOut.hs b/compiler/simplCore/FloatOut.hs index 475108c7d8..10955d2861 100644 --- a/compiler/simplCore/FloatOut.hs +++ b/compiler/simplCore/FloatOut.hs @@ -260,26 +260,21 @@ floatBody lvl arg -- Used rec rhss, and case-alternative rhss {- Note [Floating past breakpoints] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -Notes from Peter Wortmann (re: #10052) +We used to disallow floating out of breakpoint ticks (see #10052). However, I +think this is too restrictive. -"This case clearly means we're trying to float past a breakpoint..." +Consider the case of an expression scoped over by a breakpoint tick, -Further: + tick<...> (let x = ... in f x) -"Breakpoints as they currently exist are the only Tikish that is not -scoped, counting, and not splittable. +In this case it is completely legal to float out x, despite the fact that +breakpoint ticks are scoped, -This means that we can't: - - Simply float code out of it, because the payload must still be covered (scoped) - - Copy the tick, because it would change entry counts (here: duplicate breakpoints)" + let x = ... in (tick<...> f x) -While this seems like an odd case, it can apparently occur in real -life: through the combination of optimizations + GHCi usage. For an -example, see #10052 as mentioned above. So not only does the -interpreter not like some compiler-generated things (like unboxed -tuples), the compiler doesn't like interpreter-introduced things! +The reason here is that we know that the breakpoint will still be hit when the +expression is entered since the tick still scopes over the RHS. -Also see Note [GHCi and -O] in GHC.hs. -} floatExpr :: LevelledExpr @@ -318,6 +313,10 @@ floatExpr (Tick tickish expr) (fs, annotated_defns, Tick tickish expr') } -- Note [Floating past breakpoints] + | Breakpoint{} <- tickish + = case (floatExpr expr) of { (fs, floating_defns, expr') -> + (fs, floating_defns, Tick tickish expr') } + | otherwise = pprPanic "floatExpr tick" (ppr tickish) |