@@ -4164,6 +4164,10 @@ cxx_eval_increment_expression (const constexpr_ctx *ctx, tree t,
tree offset = TREE_OPERAND (t, 1);
gcc_assert (TREE_CONSTANT (offset));
+ /* OFFSET is constant, but perhaps not constant enough. We need to
+ e.g. bash FLOAT_EXPRs to REAL_CSTs. */
+ offset = fold_simple (offset);
+
/* The operand as an lvalue. */
op = cxx_eval_constant_expression (ctx, op, true,
non_constant_p, overflow_p);
new file mode 100644
@@ -0,0 +1,66 @@
+// PR c++/91705 - constexpr evaluation rejects ++/-- on floats.
+// { dg-do compile { target c++14 } }
+
+#define SA(X) static_assert((X),#X)
+
+template <class T>
+constexpr T fn1(T t)
+{
+ return ++t;
+}
+
+constexpr float fn2(float t)
+{
+ return ++t;
+}
+
+template <class T>
+constexpr T fn3(T t)
+{
+ return --t;
+}
+
+constexpr float fn4(float t)
+{
+ return --t;
+}
+
+template <class T>
+constexpr T fn5(T t)
+{
+ return t++;
+}
+
+constexpr float fn6(float t)
+{
+ return t++;
+}
+
+template <class T>
+constexpr T fn7(T t)
+{
+ return t--;
+}
+
+constexpr float fn8(float t)
+{
+ return t--;
+}
+
+constexpr double r1 = fn1(2.0f);
+SA(r1 == 3);
+constexpr double r2 = fn2(2.0f);
+SA(r2 == 3);
+constexpr double r3 = fn3(2.0f);
+SA(r3 == 1);
+constexpr double r4 = fn4(2.0f);
+SA(r4 == 1);
+
+constexpr double r5 = fn5(2.0f);
+SA(r5 == 2);
+constexpr double r6 = fn6(2.0f);
+SA(r6 == 2);
+constexpr double r7 = fn7(2.0f);
+SA(r7 == 2);
+constexpr double r8 = fn8(2.0f);
+SA(r8 == 2);