Never tick primitive string literalswip/libdw-prof

This is a more aggressive approach to the problem initially solved in
f5b275a239d2554c4da0b7621211642bf3b10650, where top-level primitive string
literals were being wrapped by ticks. This breaks the Core invariant descirbed
in Note [CoreSyn top-level string literals]. However, the previous approach was
incomplete and left several places where inappropriate ticks could sneak in.

This commit kills the problem at the source: we simply never tick any primitive
string literal expression. The assumption here is that these expressions are
destined for the top-level, where they cannot be ticked, anyways. So even if
they haven't been floated out yet there is no reason to tick them.

This partially reverts commit f5b275a239d2554c4da0b7621211642bf3b10650.

Test Plan: Validate with `-g`

Reviewers: austin, scpmw, simonpj, simonmar, dfeuer

Subscribers: dfeuer, simonmar, thomie

Differential Revision: https://phabricator.haskell.org/D3063

1 files changed, 2 insertions, 6 deletions

diff --git a/compiler/simplCore/Simplify.hs b/compiler/simplCore/Simplify.hs
index b123055387..ed2c9afa6c 100644
--- a/compiler/simplCore/Simplify.hs
+++ b/compiler/simplCore/Simplify.hs
@@ -438,15 +438,11 @@ prepareRhs mode top_lvl occ _ rhs0
         -- On the other hand, for scoping ticks we need to be able to
         -- copy them on the floats, which in turn is only allowed if
         -- we can obtain non-counting ticks.
-        | (not (tickishCounts t) || tickishCanSplit t)
+        | not (tickishCounts t) || tickishCanSplit t
         = do { (is_exp, floats, rhs') <- go n_val_args rhs
-             ; let tickIt (id, expr)
                        -- we have to take care not to tick top-level literal
                        -- strings. See Note [CoreSyn top-level string literals].
-                     | isTopLevel top_lvl && exprIsLiteralString expr
-                     = (id, expr)
-                     | otherwise
-                     = (id, mkTick (mkNoCount t) expr)
+             ; let tickIt (id, expr) = (id, mkTick (mkNoCount t) expr)
                    floats' = mapLetFloats floats tickIt
              ; return (is_exp, floats', Tick t rhs') }