Merge remote-tracking branch 'origin/topic/vern/zam-degenerate-CFT-propagation'

* origin/topic/vern/zam-degenerate-CFT-propagation:
  fixes for ZAM's propagation of control flow information for some degenerate constructs

CHANGES

@@ -1,3 +1,7 @@
+7.1.0-dev.475 | 2024-11-08 15:35:00 +0100
+
+  * fixes for ZAM's propagation of control flow information for some degenerate constructs (Vern Paxson, Corelight)
+
 7.1.0-dev.473 | 2024-11-08 15:31:39 +0100
 
   * fixed ZAM memory leak when looping over vectors of records (Vern Paxson, Corelight)

VERSION

@@ -1 +1 @@
-7.1.0-dev.473
+7.1.0-dev.475

src/script_opt/ZAM/AM-Opt.cc

@@ -1020,8 +1020,11 @@ void ZAMCompiler::BackPropagateCFT(int inst_num, ControlFlowType cf_type) {
         if ( insts1[j]->live )
             break;
 
-    // We should never wind up killing an instruction that has no predecessor.
+    // Initializations of unused variables in functions with no arguments can
-    ASSERT(j >= 0);
+    // come at the very beginning of the function, in which case there will
+    // be no predecessor to back-propagate to.
+    if ( j < 0 )
+        return;
 
     // Make sure the CFT entry is created.
     AddCFT(insts1[j], cf_type);

src/script_opt/ZAM/Stmt.cc

@@ -154,7 +154,11 @@ const ZAMStmt ZAMCompiler::IfElse(const Expr* e, const Stmt* s1, const Stmt* s2)
 
             SetV(cond_stmt, GoToTargetBeyond(branch_after_s1), branch_v);
             SetGoTo(branch_after_s1, GoToTargetBeyond(s2_end));
-            AddCFT(insts1[else_start], CFT_ELSE);
+
+            if ( else_start < insts1.size() )
+                // There was a non-empty else branch.
+                AddCFT(insts1[else_start], CFT_ELSE);
+
             AddCFT(insts1.back(), CFT_BLOCK_END);
 
             return s2_end;
@@ -848,6 +852,11 @@ const ZAMStmt ZAMCompiler::Loop(const Stmt* body) {
     auto head = StartingBlock();
     auto b = CompileStmt(body);
 
+    if ( head.stmt_num == static_cast<int>(insts1.size()) ) {
+        reporter->Error("infinite empty loop: %s", obj_desc(body).c_str());
+        return head;
+    }
+
     AddCFT(insts1[head.stmt_num], CFT_LOOP);
     AddCFT(insts1[b.stmt_num], CFT_LOOP_END);
 

testing/btest/Baseline/opt.infinite-empty-loop/.stderr

@@ -0,0 +1,3 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error: infinite empty loop: ; <...>/infinite-empty-loop.zeek, line 13
+fatal error: Optimized script execution aborted due to errors

testing/btest/Baseline/opt.null-inline/output

@@ -0,0 +1,4 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+got through the conditional #1
+got through the conditional #2
+got through the conditional #3

testing/btest/opt/infinite-empty-loop.zeek

@@ -0,0 +1,14 @@
+# @TEST-DOC: Regression tests for past ZAM bugs handling empty infinite loops
+# @TEST-REQUIRES: test "${ZEEK_USE_CPP}" != "1"
+#
+# @TEST-EXEC-FAIL: zeek -b -O ZAM %INPUT
+# @TEST-EXEC: TEST_DIFF_CANONIFIER=$SCRIPTS/diff-remove-abspath btest-diff .stderr
+
+event zeek_init()
+	{
+	# It used to be that ZAM would fault doing control-flow propagation
+	# when compiling empty infinite loops. Now it should generate a
+	# compile-time error.
+	while ( T )
+		;
+	}

testing/btest/opt/null-inline.zeek

@@ -0,0 +1,36 @@
+# @TEST-DOC: Regression tests for past ZAM bugs inlining empty functions
+# @TEST-REQUIRES: test "${ZEEK_USE_CPP}" != "1"
+#
+# @TEST-EXEC: zeek -b -O ZAM %INPUT >output
+# @TEST-EXEC: btest-diff output
+
+function empty_func1() { }
+function empty_func2() { local i: int; }
+function empty_func3() { local i = 1; }
+
+# Use a global to avoid constant propagation optimizing out the conditional.
+global bar = F;
+
+event zeek_init()
+	{
+	if ( bar )
+		empty_func1();
+	else
+		empty_func1();
+
+	print "got through the conditional #1";
+
+	if ( bar )
+		empty_func2();
+	else
+		empty_func2();
+
+	print "got through the conditional #2";
+
+	if ( bar )
+		empty_func3();
+	else
+		empty_func3();
+
+	print "got through the conditional #3";
+	}