Bug 1542279 - Fix a problem with rounding down to zero r=jonco

Differential Revision: https://phabricator.services.mozilla.com/D26463

--HG--
extra : moz-landing-system : lando

js/src/gc/Nursery.cpp

@@ -1248,7 +1248,10 @@ bool js::Nursery::maybeResizeExact(JS::GCReason reason) {
     newMaxNurseryChunksChecked = 1;
   }
   unsigned newMaxNurseryChunks = newMaxNurseryChunksChecked.value();
-  MOZ_ASSERT(newMaxNurseryChunks > 0);
+  if (newMaxNurseryChunks == 0) {
+    // The above code rounded down, but don't round down all the way to zero.
+    newMaxNurseryChunks = 1;
+  }
   if (newMaxNurseryChunks != chunkCountLimit_) {
     chunkCountLimit_ = newMaxNurseryChunks;
     /* The configured maximum nursery size is changing */

js/src/jit-test/tests/gc/bug-1542279.js

@@ -1,3 +1,8 @@
 
 gcparam('maxNurseryBytes', 2 ** 32 - 1);
+gc()
+
+gcparam('minNurseryBytes', 32*1024);
+gcparam('maxNurseryBytes', 64*1024);
+gc()