[PATCH 3/3] evaluate: warn on identical exprs on ?:

[Chris Forbes <chrisf@ijw.co.nz>]

Adds a warning when identical expressions are found on both the true and false branches of ?:. This is another common copy-paste error.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
---
 evaluate.c                                 |    8 +++++++-
 validation/check_identical_exprs_on_cond.c |   13 +++++++++++++
 2 files changed, 20 insertions(+), 1 deletions(-)
 create mode 100644 validation/check_identical_exprs_on_cond.c

diff --git a/evaluate.c b/evaluate.c
index 11de7aa..c339e63 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -898,7 +898,7 @@ static int expr_list_equiv(struct expression_list *lhs,
 int expr_equiv(struct expression *lhs, struct expression *rhs)
 {
 	/* recursively determine if lhs ~ rhs. */
-	if (!lhs ^ !rhs) return 0;
+	if (!lhs || !rhs) return 0;
 
 	if (lhs->type != rhs->type) return 0;
 	if (lhs->flags != rhs->flags) return 0;
@@ -1220,6 +1220,12 @@ static struct symbol *evaluate_conditional_expression(struct expression *expr)
 	const char * typediff;
 	int qual;
 
+	if (!preprocessing) {
+		if (expr_equiv(expr->cond_true, expr->cond_false))
+			warning(expr->pos, "identical expressions on both "
+				"branches of '?:'");
+	}
+
 	if (!evaluate_conditional(expr->conditional, 0))
 		return NULL;
 	if (!evaluate_expression(expr->cond_false))
diff --git a/validation/check_identical_exprs_on_cond.c b/validation/check_identical_exprs_on_cond.c
new file mode 100644
index 0000000..85a9938
--- /dev/null
+++ b/validation/check_identical_exprs_on_cond.c
@@ -0,0 +1,13 @@
+extern void bar(void);
+
+static void foo(void *a, void *b, void *c)
+{
+	void * d = a ? b : b; /* should warn */
+}
+/*
+ * check-name: A warning should be issued for identical expressions on both the true and false branches of the '?:' operator.
+ *
+ * check-error-start
+check_identical_exprs_on_cond.c:5:22: warning: identical expressions on both branches of '?:'
+ * check-error-end
+ */
-- 
1.7.4.1