c++: ICE with -Wtautological-compare in template [PR116534]

Pre r14-4793, we'd call warn_tautological_cmp -> operand_equal_p
with operands wrapped in NON_DEPENDENT_EXPR, which works, since
o_e_p bails for codes it doesn't know.  But now we pass operands
not encapsulated in NON_DEPENDENT_EXPR, and crash, because the
template tree for &a[x] has null DECL_FIELD_OFFSET.

This patch extends r12-7797 to cover the case when DECL_FIELD_OFFSET
is null.

	PR c++/116534

gcc/ChangeLog:

	* fold-const.cc (operand_compare::operand_equal_p): If either
	field's DECL_FIELD_OFFSET is null, compare the fields with ==.

gcc/testsuite/ChangeLog:

	* g++.dg/warn/Wtautological-compare4.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>
(cherry picked from commit 7ca486889b1b1c7e7bcbbca3b6caa103294ec07d)

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 869f6363560d8478ddcc5c7795fc876fb9714470..1e6b573ca01a7184612b0c2f98fe93055dbd73a7 100644 (file)
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -3578,9 +3578,15 @@ operand_compare::operand_equal_p (const_tree arg0, const_tree arg1,
 
                    /* Non-FIELD_DECL operands can appear in C++ templates.  */
                    if (TREE_CODE (field0) != FIELD_DECL
-                       || TREE_CODE (field1) != FIELD_DECL
-                       || !operand_equal_p (DECL_FIELD_OFFSET (field0),
-                                            DECL_FIELD_OFFSET (field1), flags)
+                       || TREE_CODE (field1) != FIELD_DECL)
+                     return false;
+
+                   if (!DECL_FIELD_OFFSET (field0)
+                       || !DECL_FIELD_OFFSET (field1))
+                     return field0 == field1;
+
+                   if (!operand_equal_p (DECL_FIELD_OFFSET (field0),
+                                         DECL_FIELD_OFFSET (field1), flags)
                        || !operand_equal_p (DECL_FIELD_BIT_OFFSET (field0),
                                             DECL_FIELD_BIT_OFFSET (field1),
                                             flags))

diff --git a/gcc/testsuite/g++.dg/warn/Wtautological-compare4.C b/gcc/testsuite/g++.dg/warn/Wtautological-compare4.C
new file mode 100644 (file)
index 0000000..96308f4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wtautological-compare4.C
@@ -0,0 +1,21 @@
+// PR c++/116534
+// { dg-do compile }
+// { dg-options "-Wall" }
+
+template <class A>
+struct Test {
+    bool foo(unsigned x, unsigned y) {
+        bool test = &a[x] == &b[y];
+       return test;
+    }
+    unsigned *a;
+    unsigned *b;
+};
+
+void
+g ()
+{
+  Test<int> t;
+  t.foo (0u, 1u);
+  t.foo (0u, 0u);
+}