fix removing 1 / 0

Author: Frotty

de.peeeq.wurstscript/src/main/java/de/peeeq/wurstscript/translation/imoptimizer/ImOptimizer.java

@@ -2,6 +2,7 @@
 
 import com.google.common.collect.Lists;
 import de.peeeq.wurstio.TimeTaker;
+import de.peeeq.wurstscript.WurstOperator;
 import de.peeeq.wurstscript.WLogger;
 import de.peeeq.wurstscript.intermediatelang.optimizer.BranchMerger;
 import de.peeeq.wurstscript.intermediatelang.optimizer.ConstantAndCopyPropagation;
@@ -201,10 +202,34 @@ private List<ImExpr> collectSideEffects(ImExpr expr, SideEffectAnalyzer analyzer
         if (expr == null) {
             return Collections.emptyList();
         }
+        if (mayTrapAtRuntime(expr)) {
+            return Collections.singletonList(expr);
+        }
         if (analyzer.hasObservableSideEffects(expr, func -> func.isNative()
             && UselessFunctionCallsRemover.isFunctionWithoutSideEffect(func.getName()))) {
             return Collections.singletonList(expr);
         }
         return Collections.emptyList();
     }
+
+    private boolean mayTrapAtRuntime(Element elem) {
+        if (elem instanceof ImOperatorCall) {
+            ImOperatorCall opCall = (ImOperatorCall) elem;
+            WurstOperator op = opCall.getOp();
+            if ((op == WurstOperator.DIV_INT || op == WurstOperator.MOD_INT) && opCall.getArguments().size() >= 2) {
+                ImExpr denominator = opCall.getArguments().get(1);
+                // Preserve integer div/mod unless denominator is provably non-zero.
+                if (!(denominator instanceof ImIntVal) || ((ImIntVal) denominator).getValI() == 0) {
+                    return true;
+                }
+            }
+        }
+        for (int i = 0; i < elem.size(); i++) {
+            Element child = elem.get(i);
+            if (mayTrapAtRuntime(child)) {
+                return true;
+            }
+        }
+        return false;
+    }
 }

de.peeeq.wurstscript/src/test/java/tests/wurstscript/tests/OptimizerTests.java

@@ -599,6 +599,20 @@ public void test_unused_func_remover2() throws IOException {
         assertTrue(compiledAndOptimized.contains("I2S"), "I2S should not be removed");
     }
 
+    @Test
+    public void deadStoreKeepsPotentialDivisionTrap() throws IOException {
+        test().executeProg(false).lines(
+            "package test",
+            "	@extern native I2S(int i) returns string",
+            "	native getY() returns int",
+            "	init",
+            "		int y = getY()",
+            "		string x = I2S(1 div y)",
+            "endpackage");
+        String compiledNoOpt = Files.toString(new File("test-output/OptimizerTests_deadStoreKeepsPotentialDivisionTrap_no_opts.j"), Charsets.UTF_8);
+        assertTrue(compiledNoOpt.contains("1 /"), "potential division trap should be preserved");
+    }
+
     @Test
     public void test_unreachableCodeRemover() throws IOException {
         test().withStdLib().lines(