SKIP_STACK_IN_SMALL option

2 files changed, 7 insertions, 5 deletions

diff --git a/src/runtime.js b/src/runtime.js
index 0b809d6b..c99d9d6f 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -30,10 +30,7 @@ RuntimeGenerator = {
   },
 
   stackEnter: function(initial) {
-    if (initial === 0) return ''; // Note that we don't even push the stack! This is faster, but
-                                  // means that we don't clear stack allocations done in this function
-                                  // until the parent unwinds its stack. So potentially if we are in
-                                  // a loop, we can use a lot of memory.
+    if (initial === 0 && SKIP_STACK_IN_SMALL) return '';
     var ret = 'var __stackBase__  = STACKTOP; STACKTOP += ' + initial;
     if (ASSERTIONS) {
       ret += '; assert(STACKTOP < STACK_MAX)';
@@ -45,7 +42,7 @@ RuntimeGenerator = {
   },
 
   stackExit: function(initial) {
-    if (initial === 0) return ''; // See comment in stackEnter
+    if (initial === 0 && SKIP_STACK_IN_SMALL) return '';
     var ret = '';
     if (SAFE_HEAP) {
       ret += 'for (var i = __stackBase__; i < STACKTOP; i++) SAFE_HEAP_CLEAR(i);';
diff --git a/src/settings.js b/src/settings.js
index 7fd9f17c..0243a191 100644
--- a/src/settings.js
+++ b/src/settings.js
@@ -38,6 +38,11 @@ INIT_HEAP = 0; // Whether to initialize memory anywhere other than the stack to
 OPTIMIZE = 0; // Optimize llvm operations into js commands
 RELOOP = 0; // Recreate js native loops from llvm data
 USE_TYPED_ARRAYS = 0; // Try to use typed arrays for the heap
+SKIP_STACK_IN_SMALL = 1; // When enabled, does not push/pop the stack at all in
+                         // functions that have no basic stack usage. But, they
+                         // may allocate stack later, and in a loop, this can be
+                         // very bad. In particular, when debugging, printf()ing
+                         // a lot can exhaust the stack very fast, with this option.
 
 // Generated code debugging options
 SAFE_HEAP = 0; // Check each write to the heap against a list of blocked addresses