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| author | Joachim Breitner <mail@joachim-breitner.de> | 2014-07-22 10:37:56 +0200 |
|---|---|---|
| committer | Joachim Breitner <mail@joachim-breitner.de> | 2014-07-22 10:37:56 +0200 |
| commit | 1c126cfb4a9067d4ac5987d9371f6920328f6f29 (patch) | |
| tree | 5492f65fe27a1c48443263d7b945fa297c0cfa0a | |
| parent | 7aabfa6292c2469cf3250e006869273fb1b356ce (diff) | |
| download | haskell-wip/T9339.tar.gz | |
Make last a good consumerwip/T9339
simply by implementing it as foldl. This fixes #9339. Thanks to David
Feuer for bringing it up.
| -rw-r--r-- | libraries/base/GHC/List.lhs | 7 | ||||
| -rw-r--r-- | testsuite/tests/perf/should_run/T9339.hs | 4 | ||||
| -rw-r--r-- | testsuite/tests/perf/should_run/T9339.stdout | 1 | ||||
| -rw-r--r-- | testsuite/tests/perf/should_run/all.T | 9 |
4 files changed, 16 insertions, 5 deletions
diff --git a/libraries/base/GHC/List.lhs b/libraries/base/GHC/List.lhs index e004ded1e8..9b6cc2eb19 100644 --- a/libraries/base/GHC/List.lhs +++ b/libraries/base/GHC/List.lhs @@ -83,11 +83,8 @@ last [x] = x last (_:xs) = last xs last [] = errorEmptyList "last" #else --- eliminate repeated cases -last [] = errorEmptyList "last" -last (x:xs) = last' x xs - where last' y [] = y - last' _ (y:ys) = last' y ys +-- use foldl to allow fusion +last = foldl (\_ x -> x) (errorEmptyList "last") #endif -- | Return all the elements of a list except the last one. diff --git a/testsuite/tests/perf/should_run/T9339.hs b/testsuite/tests/perf/should_run/T9339.hs new file mode 100644 index 0000000000..96f5f7201a --- /dev/null +++ b/testsuite/tests/perf/should_run/T9339.hs @@ -0,0 +1,4 @@ +-- Tests that `last` successfully fuses. + +main :: IO () +main = print $ last $ filter odd $ [1::Int ..10000000] diff --git a/testsuite/tests/perf/should_run/T9339.stdout b/testsuite/tests/perf/should_run/T9339.stdout new file mode 100644 index 0000000000..e161ae3694 --- /dev/null +++ b/testsuite/tests/perf/should_run/T9339.stdout @@ -0,0 +1 @@ +9999999 diff --git a/testsuite/tests/perf/should_run/all.T b/testsuite/tests/perf/should_run/all.T index a9d7c0325d..924f7f15b8 100644 --- a/testsuite/tests/perf/should_run/all.T +++ b/testsuite/tests/perf/should_run/all.T @@ -379,3 +379,12 @@ test('T9203', only_ways(['normal'])], compile_and_run, ['-O2']) + +test('T9339', + [stats_num_field('bytes allocated', + [ (wordsize(64), 80050760, 5) ]), + # w/o fusing last: 320005080 + # 2014-07-22: 80050760 + only_ways(['normal'])], + compile_and_run, + ['-O2']) |