fixed incorrect ZAM optimization of expressions seen in single-statement inlined functions

src/script_opt/GenIDDefs.cc

@@ -92,11 +92,18 @@ TraversalCode GenIDDefs::PreStmt(const Stmt* s) {
                     st->Traverse(this);
                 }
             }
-            else
-                // If there's just a single statement then there are no
-                // expressions computed subsequent to it that we need to
-                // worry about, so just do ordinary traversal.
+            else {
+                // If there's just a single statement then there are two
+                // possibilities. If the statement is atomic (no sub-statements)
+                // then given that it's in reduced form, it's not going to have
+                // any expressions that we can leverage. OTOH, if it's compound
+                // (if/for/while/switch) then there's no safe re-using of
+                // expressions within it since they may-or-may-not wind up
+                // being computed. So we should always start a new block.
+                StartConfluenceBlock(s);
+                did_confluence = true;
                 block->Traverse(this);
+            }
 
             if ( did_confluence )
                 EndConfluenceBlock();

testing/btest/Baseline/opt.regress-inlining-temps/output

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+T, [field1=3], 3

testing/btest/opt/regress-inlining-temps.zeek

@@ -0,0 +1,30 @@
+# @TEST-DOC: Regression test for incorrect reuse of temporaries when inlining
+# @TEST-REQUIRES: test "${ZEEK_USE_CPP}" != "1"
+# @TEST-EXEC: zeek -b -O ZAM %INPUT >output
+# @TEST-EXEC: btest-diff output
+
+type R: record {
+	field1: count;
+};
+
+global yes = T;
+
+function pred(my_R: R): bool
+	{
+	# In the following, my_R$field1 will never be evaluated ...
+	if ( yes || my_R$field1 == 4 )
+		return T;
+	else
+		return F;
+	}
+
+event zeek_init()
+	{
+	local my_R = R($field1=3);
+
+	# ... prior to the regression, the third argument in this print
+	# was taken from the temporary in pred() that *would* have held
+	# my_R$field1 had that ever been evaluated, but instead it holds
+	# the default ZVal value of 0.
+	print pred(my_R), my_R, my_R$field1;
+	}