proper support for bitfields

2 files changed, 11 insertions, 2 deletions

diff --git a/src/jsifier.js b/src/jsifier.js
index e5ab6b4c..17fe4fd3 100644
--- a/src/jsifier.js
+++ b/src/jsifier.js
@@ -749,7 +749,15 @@ function JSify(data, functionsOnly, givenTypes, givenFunctions) {
           default: throw 'Unknown fcmp variant: ' + variant
         }
       }
-      case 'zext': case 'fpext': case 'trunc': case 'sext': case 'fptrunc': return ident1;
+      case 'zext': case 'fpext': case 'sext': case 'fptrunc': return ident1;
+      case 'trunc': {
+        // Unlike extending, which we just 'do' (by doing nothing),
+        // truncating can change the number, e.g. by truncating to an i1
+        // in order to get the first bit
+        assert(ident2[0] == 'i');
+        var bitsLeft = ident2.substr(1);
+        return '((' + ident1 + ') & ' + (Math.pow(2, bitsLeft)-1) + ')';
+      }
       case 'select': return ident1 + ' ? ' + ident2 + ' : ' + ident3;
       case 'ptrtoint': {
         //if (type != 'i8*') print('// XXX Warning: Risky ptrtoint operation on line ' + lineNum);
diff --git a/src/preamble.js b/src/preamble.js
index 7ae7e0ad..aa58e172 100644
--- a/src/preamble.js
+++ b/src/preamble.js
@@ -35,7 +35,8 @@ function SAFE_HEAP_ACCESS(dest, type, store) {
     }
     var history = HEAP_HISTORY[dest];
     if (history === null) return;
-    assert(history, 'Must have a history for a safe heap load!');
+    assert(history, 'Must have a history for a safe heap load!'); // Warning - bit fields in C structs cause loads+stores for each store, so
+                                                                  //           they will show up here...
 //    assert((history && history[0]) /* || HEAP[dest] === 0 */, "Loading from where there was no store! " + dest + ',' + HEAP[dest] + ',' + type + ', \n\n' + new Error().stack + '\n');
 //    if (history[0].type !== type) {
     if (history !== type) {