memory growth must be manually enabled with ALLOW_MEMORY_GROWTH, in which case the eliminator runs in safe mode

2 files changed, 12 insertions, 1 deletions

diff --git a/src/preamble.js b/src/preamble.js
index b197ef02..24277014 100644
--- a/src/preamble.js
+++ b/src/preamble.js
@@ -576,9 +576,12 @@ var STACK_ROOT, STACKTOP, STACK_MAX;
 var STATICTOP;
 #if USE_TYPED_ARRAYS
 function enlargeMemory() {
+#if ALLOW_MEMORY_GROWTH == 0
+  abort('Cannot enlarge memory arrays. Adjust TOTAL_MEMORY or compile with ALLOW_MEMORY_GROWTH');
+#else
   // TOTAL_MEMORY is the current size of the actual array, and STATICTOP is the new top.
 #if ASSERTIONS
-  Module.printErr('Warning: Enlarging memory arrays, this is not fast, and can also break in high optimization levels where we assume globals are not modified! ' + [STATICTOP, TOTAL_MEMORY]); // XXX perhaps never do elimination optimizations of calls that can lead to resizing, to avoid HEAP[malloc()] = X; where JS semantic will write to the old HEAP if malloc replaces it
+  Module.printErr('Warning: Enlarging memory arrays, this is not fast, and ALLOW_MEMORY_GROWTH is not fully tested with all optimizations on! ' + [STATICTOP, TOTAL_MEMORY]); // We perform safe elimination instead of elimination in this mode, but if you see this error, try to disable it and other optimizations entirely
   assert(STATICTOP >= TOTAL_MEMORY);
   assert(TOTAL_MEMORY > 4); // So the loop below will not be infinite
 #endif
@@ -609,6 +612,7 @@ function enlargeMemory() {
   HEAPF64 = new Float64Array(buffer);
   HEAP8.set(oldHEAP8);
 #endif
+#endif
 }
 #endif
 
diff --git a/src/settings.js b/src/settings.js
index a1c41de7..7e7caa6f 100644
--- a/src/settings.js
+++ b/src/settings.js
@@ -48,6 +48,13 @@ var TOTAL_MEMORY = 10*1024*1024; // The total amount of memory to use. Using mor
                                  // we need to copy the old heap into a new one in that case.
 var FAST_MEMORY = 2*1024*1024; // The amount of memory to initialize to 0. This ensures it will be
                                // in a flat array. This only matters in non-typed array builds.
+var ALLOW_MEMORY_GROWTH = 0; // If false, we abort with an error if we try to allocate more memory than
+                             // we can (TOTAL_MEMORY). If true, we will grow the memory arrays at
+                             // runtime, seamlessly and dynamically. This has a performance cost though,
+                             // both during the actual growth and in general (the latter is because in
+                             // that case we must be careful about optimizations, in particular the
+                             // eliminator). Note that memory growth is only supported with typed
+                             // arrays.
 
 // Code embetterments
 var MICRO_OPTS = 1; // Various micro-optimizations, like nativizing variables