Improve accuracy of get/setAllocationCounter

Summary:
get/setAllocationCounter didn't take into account allocations in the
current block. This was known at the time, but it turns out to be
important to have more accuracy when using these in a fine-grained
way.

Test Plan:
New unit test to test incrementally larger allocaitons.  Before I got
results like this:

```
+0
+0
+0
+0
+0
+4096
+0
+0
+0
+0
+0
+4064
+0
+0
+4088
+4056
+0
+0
+0
+4088
+4096
+4056
+4096
```

Notice how the results aren't always monotonically increasing.  After
this patch:

```
+344
+416
+488
+560
+632
+704
+776
+848
+920
+992
+1064
+1136
+1208
+1280
+1352
+1424
+1496
+1568
+1640
+1712
+1784
+1856
+1928
+2000
+2072
+2144
```

Reviewers: niteria, bgamari, hvr, erikd

Subscribers: rwbarton, thomie, carter

Differential Revision: https://phabricator.haskell.org/D4288

1 files changed, 19 insertions, 0 deletions

diff --git a/testsuite/tests/rts/alloccounter1.hs b/testsuite/tests/rts/alloccounter1.hs
new file mode 100644
index 0000000000..4b81896d2c
--- /dev/null
+++ b/testsuite/tests/rts/alloccounter1.hs
@@ -0,0 +1,19 @@
+module Main where
+
+import Control.Exception
+import Control.Monad
+import Data.List
+import System.Mem
+
+main = do
+  let
+    testAlloc n = do
+      let start = 999999
+      setAllocationCounter start
+      evaluate (last [1..n])
+      c <- getAllocationCounter
+      -- print (start - c)
+      return (start - c)
+  results <- forM [1..1000] testAlloc
+  print (sort results == results)
+    -- results better be in ascending order