DCE fixes

Author: Frotty

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

@@ -213,6 +213,22 @@ private List<ImExpr> collectSideEffects(ImExpr expr, SideEffectAnalyzer analyzer
     }
 
     private boolean mayTrapAtRuntime(Element elem) {
+        return mayTrapAtRuntime(elem, new HashMap<>(), new LinkedHashSet<>());
+    }
+
+    private boolean mayTrapAtRuntime(Element elem, Map<ImFunction, Boolean> functionCache, Set<ImFunction> inProgress) {
+        if (elem instanceof ImFunctionCall) {
+            ImFunction calledFunc = ((ImFunctionCall) elem).getFunc();
+            if (functionMayTrapAtRuntime(calledFunc, functionCache, inProgress)) {
+                return true;
+            }
+        } else if (elem instanceof ImMethodCall) {
+            ImFunction calledFunc = ((ImMethodCall) elem).getMethod().getImplementation();
+            if (calledFunc == null || functionMayTrapAtRuntime(calledFunc, functionCache, inProgress)) {
+                return true;
+            }
+        }
+
         if (elem instanceof ImOperatorCall) {
             ImOperatorCall opCall = (ImOperatorCall) elem;
             WurstOperator op = opCall.getOp();
@@ -226,10 +242,31 @@ private boolean mayTrapAtRuntime(Element elem) {
         }
         for (int i = 0; i < elem.size(); i++) {
             Element child = elem.get(i);
-            if (mayTrapAtRuntime(child)) {
+            if (mayTrapAtRuntime(child, functionCache, inProgress)) {
                 return true;
             }
         }
         return false;
     }
+
+    private boolean functionMayTrapAtRuntime(ImFunction function, Map<ImFunction, Boolean> functionCache, Set<ImFunction> inProgress) {
+        if (function.isNative()) {
+            return false;
+        }
+
+        Boolean cachedResult = functionCache.get(function);
+        if (cachedResult != null) {
+            return cachedResult;
+        }
+
+        if (!inProgress.add(function)) {
+            // Recursive cycles are conservatively treated as potentially trapping.
+            return true;
+        }
+
+        boolean mayTrap = mayTrapAtRuntime(function.getBody(), functionCache, inProgress);
+        inProgress.remove(function);
+        functionCache.put(function, mayTrap);
+        return mayTrap;
+    }
 }

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

@@ -613,6 +613,22 @@ public void deadStoreKeepsPotentialDivisionTrap() throws IOException {
         assertTrue(compiledNoOpt.contains("1 /"), "potential division trap should be preserved");
     }
 
+    @Test
+    public void deadStoreKeepsPotentialDivisionTrapInCallee() throws IOException {
+        test().executeProg(false).lines(
+            "package test",
+            "	@extern native I2S(int i) returns string",
+            "	native getY() returns int",
+            "	function wrap(int y) returns int",
+            "		return 1 div y",
+            "	init",
+            "		int y = getY()",
+            "		string x = I2S(wrap(y))",
+            "endpackage");
+        String compiledNoOpt = Files.toString(new File("test-output/OptimizerTests_deadStoreKeepsPotentialDivisionTrapInCallee_no_opts.j"), Charsets.UTF_8);
+        assertTrue(compiledNoOpt.contains("1 /"), "potential division trap in callee should be preserved");
+    }
+
     @Test
     public void test_unreachableCodeRemover() throws IOException {
         test().withStdLib().lines(