Revert "CoreTidy: Don't seq unfoldings"

This reverts commit b3da6a6c as it
reintroduces the original space leak.

compiler/coreSyn/CoreTidy.hs

@@ -15,7 +15,7 @@ module CoreTidy (
 #include "HsVersions.h"
 
 import CoreSyn
-import CoreUnfold ( mkCoreUnfolding )
+import CoreSeq ( seqUnfolding )
 import CoreArity
 import Id
 import IdInfo
@@ -221,21 +221,17 @@ tidyUnfolding tidy_env df@(DFunUnfolding { df_bndrs = bndrs, df_args = args }) _
     (tidy_env', bndrs') = tidyBndrs tidy_env bndrs
 
 tidyUnfolding tidy_env
-              (CoreUnfolding { uf_tmpl = unf_rhs, uf_is_top = top_lvl
-                             , uf_src = src, uf_guidance = guidance })
+              unf@(CoreUnfolding { uf_tmpl = unf_rhs, uf_src = src })
               unf_from_rhs
   | isStableSource src
-  = mkCoreUnfolding src top_lvl (tidyExpr tidy_env unf_rhs) guidance
-    -- Preserves OccInfo
-
-    -- Note that uf_is_value and friends may be a thunk containing a reference
-    -- to the old template. Consequently it is important that we rebuild them,
-    -- despite the fact that they won't change, to avoid a space leak (since,
-    -- e.g., ToIface doesn't look at them; see #13564). This is the same
-    -- approach we use in Simplify.simplUnfolding and TcIface.tcUnfolding.
+  = seqIt $ unf { uf_tmpl = tidyExpr tidy_env unf_rhs }    -- Preserves OccInfo
+    -- This seqIt avoids a space leak: otherwise the uf_is_value,
+    -- uf_is_conlike, ... fields may retain a reference to the
+    -- pre-tidied expression forever (ToIface doesn't look at them)
 
   | otherwise
   = unf_from_rhs
+  where seqIt unf = seqUnfolding unf `seq` unf
 tidyUnfolding _ unf _ = unf     -- NoUnfolding or OtherCon
 
 {-

testsuite/tests/perf/compiler/all.T

@@ -744,7 +744,7 @@ test('T9020',
 test('T9675',
      [ only_ways(['optasm']),
        compiler_stats_num_field('max_bytes_used', # Note [residency]
-          [(wordsize(64), 25381032, 15),
+          [(wordsize(64), 17675240, 15),
           # 2014-10-13    29596552
           # 2014-10-13    26570896   seq the DmdEnv in seqDmdType as well
           # 2014-10-13    18582472   different machines giving different results..
@@ -755,13 +755,12 @@ test('T9675',
           # 2016-03-14    38776008   Final demand analyzer run
           # 2016-04-01    29871032   Fix leaks in demand analysis
           # 2016-04-30    17675240   Fix leaks in tidy unfoldings
-          # 2017-05-08    25381032   CoreTidy: Don't seq unfoldings
            (wordsize(32), 18043224, 15)
           # 2015-07-11    15341228   (x86/Linux, 64-bit machine) use +RTS -G1
           # 2016-04-06    18043224   (x86/Linux, 64-bit machine)
           ]),
        compiler_stats_num_field('peak_megabytes_allocated', # Note [residency]
-          [(wordsize(64), 94, 15),
+          [(wordsize(64), 63, 15),
           # 2014-10-13    66
           # 2014-10-13    58         seq the DmdEnv in seqDmdType as well
           # 2014-10-13    49         different machines giving different results...
@@ -773,7 +772,6 @@ test('T9675',
           # 2016-04-14    144        Final demand analyzer run
           # 2016-07-26    121        Unboxed sums?
           # 2017-04-30    63         Fix leaks in tidy unfoldings
-          # 2017-05-08    94         CoreTidy: Don't seq unfoldings
             (wordsize(32), 56, 15)
           # 2015-07-11    56         (x86/Linux, 64-bit machine) use +RTS -G1
           ]),