make function pointer aliasing configurable

3 files changed, 9 insertions, 5 deletions

diff --git a/src/modules.js b/src/modules.js
index 9662200c..d9888c24 100644
--- a/src/modules.js
+++ b/src/modules.js
@@ -234,7 +234,7 @@ var Types = {
   preciseI64MathUsed: (PRECISE_I64_MATH == 2)
 };
 
-var firstTableIndex = (ASM_JS ? 2*RESERVED_FUNCTION_POINTERS : 0) + 2;
+var firstTableIndex = FUNCTION_POINTER_ALIGNMENT * ((ASM_JS ? RESERVED_FUNCTION_POINTERS : 0) + 1);
 
 var Functions = {
   // All functions that will be implemented in this file. Maps id to signature
@@ -287,7 +287,7 @@ var Functions = {
       ret = this.indexedFunctions[ident];
       if (!ret) {
         ret = this.nextIndex;
-        this.nextIndex += 2; // Need to have indexes be even numbers, see |polymorph| test
+        this.nextIndex += FUNCTION_POINTER_ALIGNMENT;
         this.indexedFunctions[ident] = ret;
       }
       ret = ret.toString();
diff --git a/src/runtime.js b/src/runtime.js
index 00031fed..a281045b 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -347,22 +347,23 @@ var Runtime = {
     for (var i = 0; i < Runtime.functionPointers.length; i++) {
       if (!Runtime.functionPointers[i]) {
         Runtime.functionPointers[i] = func;
-        return 2 + 2*i;
+        return {{{ FUNCTION_POINTER_ALIGNMENT }}}*(1 + i);
       }
     }
     throw 'Finished up all reserved function pointers. Use a higher value for RESERVED_FUNCTION_POINTERS.';
 #else
     var table = FUNCTION_TABLE;
     var ret = table.length;
+    assert(ret % {{{ FUNCTION_POINTER_ALIGNMENT }}} === 0);
     table.push(func);
-    table.push(0);
+    for (var i = 0; i < {{{ FUNCTION_POINTER_ALIGNMENT }}}-1; i++) table.push(0);
     return ret;
 #endif
   },
 
   removeFunction: function(index) {
 #if ASM_JS
-    Runtime.functionPointers[(index-2)/2] = null;
+    Runtime.functionPointers[(index-{{{ FUNCTION_POINTER_ALIGNMENT }}})/{{{ FUNCTION_POINTER_ALIGNMENT }}}] = null;
 #else
     var table = FUNCTION_TABLE;
     table[index] = null;
diff --git a/src/settings.js b/src/settings.js
index 5cf054a9..3eb43f1c 100644
--- a/src/settings.js
+++ b/src/settings.js
@@ -170,6 +170,9 @@ var ALIASING_FUNCTION_POINTERS = 0; // Whether to allow function pointers to ali
                                     // a different type. This can greatly decrease table sizes
                                     // in asm.js, but can break code that compares function
                                     // pointers across different types.
+var FUNCTION_POINTER_ALIGNMENT = 2; // Byte alignment of function pointers - we will fill the
+                                    // tables with zeros on aligned values. 1 means all values
+                                    // are aligned and all will be used (which is optimal).
 
 var ASM_HEAP_LOG = 0; // Simple heap logging, like SAFE_HEAP_LOG but cheaper, and in asm.js