Fix increment/decrement not wrapping small ints in simplified case, see #26

src/compiler.ts

@@ -3343,32 +3343,42 @@ export class Compiler extends DiagnosticEmitter {
         throw new Error("unary postfix operator expected");
     }
 
+    var setValue: ExpressionRef;
+    var tempLocal: Local | null = null;
+
     // simplify if dropped anyway
-    if (contextualType == Type.void)
-      return this.compileAssignmentWithValue(expression.operand,
-        this.module.createBinary(op,
-          getValue,
-          nativeOne
-        ), false
+    if (contextualType == Type.void) {
+      setValue = this.module.createBinary(op,
+        getValue,
+        nativeOne
       );
 
-    // use a temp local for the intermediate value and prepare a setter
-    var tempLocal = this.currentFunction.getTempLocal(this.currentType);
-    var setValue = this.module.createBinary(op,
-      this.module.createGetLocal(tempLocal.index, nativeType),
-      nativeOne
-    );
+    // otherwise use a temp local for the intermediate value
+    } else {
+      tempLocal = this.currentFunction.getTempLocal(this.currentType);
+      setValue = this.module.createBinary(op,
+        this.module.createGetLocal(tempLocal.index, nativeType),
+        nativeOne
+      );
+    }
+
     if (possiblyOverflows) {
       assert(this.currentType.is(TypeFlags.SMALL | TypeFlags.INTEGER));
       setValue = makeSmallIntegerWrap(setValue, this.currentType, this.module);
     }
+
     setValue = this.compileAssignmentWithValue(expression.operand, setValue, false); // sets currentType = void
-    this.currentType = tempLocal.type;
-    this.currentFunction.freeTempLocal(tempLocal);
+    if (contextualType == Type.void) {
+      assert(!tempLocal);
+      return setValue;
+    }
+
+    this.currentType = assert(tempLocal).type;
+    this.currentFunction.freeTempLocal(<Local>tempLocal);
     return this.module.createBlock(null, [
-      this.module.createSetLocal(tempLocal.index, getValue),
+      this.module.createSetLocal((<Local>tempLocal).index, getValue),
       setValue,
-      this.module.createGetLocal(tempLocal.index, nativeType)
+      this.module.createGetLocal((<Local>tempLocal).index, nativeType)
     ], nativeType);
   }
 

tests/compiler/overflow.ts

@@ -1,47 +1,130 @@
-// see also: https://github.com/AssemblyScript/assemblyscript/issues/26
+// becomes simplified: val++
+// uses a temp. local: ctx = val++
 
-var badByte: u8 = 0xFF;
-badByte += 1;
-assert(badByte == 0);
+// i8
+{
+  let val: i8 = 127;
+  let ctx: i8;
 
-var anotherBadByte: u8 = 0xFF;
-var badIncrementer: u8 = 1;
-anotherBadByte += badIncrementer;
-assert(anotherBadByte == 0);
+  val++;
+  assert(val == -128);
 
-function local(): void {
-  var badByte: u8 = 0xFF;
-  badByte += 1;
-  assert(badByte == 0);
+  val--;
+  assert(val == 127);
 
-  var anotherBadByte: u8 = 0xFF;
-  var badIncrementer: u8 = 1;
-  anotherBadByte += badIncrementer;
-  assert(anotherBadByte == 0);
+  ctx = val++;
+  assert(val == -128);
+
+  ctx = val--;
+  assert(val == 127);
+
+  ++val;
+  assert(val == -128);
+
+  --val;
+  assert(val == 127);
+
+  ctx = ++val;
+  assert(val == -128);
+
+  ctx = --val;
+  assert(val == 127);
+
+  assert(val + 1 == -128);
 }
 
-local();
+// i16
+{
+  let val: i16 = 32767;
+  let ctx: i16;
 
-function loadU8FF(): u8 {
-  store<u8>(0, 0xff);
-  return load<u8>(0);
+  val++;
+  assert(val == -32768);
+
+  val--;
+  assert(val == 32767);
+
+  ctx = val++;
+  assert(val == -32768);
+
+  ctx = val--;
+  assert(val == 32767);
+
+  ++val;
+  assert(val == -32768);
+
+  --val;
+  assert(val == 32767);
+
+  ctx = ++val;
+  assert(val == -32768);
+
+  ctx = --val;
+  assert(val == 32767);
+
+  assert(val + 1 == -32768);
 }
 
-var valueU8: u8 = loadU8FF();
-valueU8 += 1;
-assert(valueU8 == 0);
+// u8
+{
+  let val: u8 = 0;
+  let ctx: u8;
 
-function storeU8FFadd1(val: u8): void {
-  store<u8>(0, val);
-  assert(load<u8>(0) == 0);
+  val--;
+  assert(val == 0xff);
+
+  val++;
+  assert(val == 0);
+
+  ctx = val--;
+  assert(val == 0xff);
+
+  ctx = val++;
+  assert(val == 0);
+
+  --val;
+  assert(val == 0xff);
+
+  ++val;
+  assert(val == 0);
+
+  ctx = --val;
+  assert(val == 0xff);
+
+  ctx = ++val;
+  assert(val == 0);
+
+  assert(val - 1 == 0xff);
 }
 
-valueU8 = 0xFF;
-storeU8FFadd1(valueU8 + 1);
+// u16
+{
+  let val: u16 = 0;
+  let ctx: u16;
 
-store<u8>(0, valueU8 + 1);
-assert(load<u8>(0) == 0);
+  val--;
+  assert(val == 0xffff);
 
-store<u8>(0, ++valueU8);
-assert(load<u8>(0) == 0);
-assert(valueU8 == 0);
+  val++;
+  assert(val == 0);
+
+  ctx = val--;
+  assert(val == 0xffff);
+
+  ctx = val++;
+  assert(val == 0);
+
+  --val;
+  assert(val == 0xffff);
+
+  ++val;
+  assert(val == 0);
+
+  ctx = --val;
+  assert(val == 0xffff);
+
+  ctx = ++val;
+  assert(val == 0);
+
+  assert(val - 1 == 0xffff);
+}