Improve compile times by enabling +RTS -H for GHC (only when bootstrapped)

1 files changed, 8 insertions, 0 deletions

diff --git a/ghc/hschooks.c b/ghc/hschooks.c
index 232ac08045..b8a720b209 100644
--- a/ghc/hschooks.c
+++ b/ghc/hschooks.c
@@ -18,7 +18,15 @@ in instead of the defaults.
 void
 defaultsHook (void)
 {
+#if __GLASGOW_HASKELL__ >= 707
+    // This helps particularly with large compiles, but didn't work
+    // very well with earlier GHCs because it caused large amounts of
+    // fragmentation.  See rts/sm/BlockAlloc.c:allocLargeChunk().
+    RtsFlags.GcFlags.heapSizeSuggestionAuto = rtsTrue;
+#else
     RtsFlags.GcFlags.heapSizeSuggestion = 6*1024*1024 / BLOCK_SIZE;
+#endif
+
     RtsFlags.GcFlags.maxStkSize         = 512*1024*1024 / sizeof(W_);
     RtsFlags.GcFlags.giveStats = COLLECT_GC_STATS;