Hi! The following patch fixes ICE where we try to store a[-1]. The problem is that we don't check the bounds first and then later on we assert it is not negative.
Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2017-02-21 Jakub Jelinek <[email protected]> PR c++/79655 * constexpr.c (cxx_eval_array_reference): Diagnose negative subscript. * g++.dg/cpp1y/constexpr-79655.C: New test. --- gcc/cp/constexpr.c.jj 2017-02-17 18:29:21.000000000 +0100 +++ gcc/cp/constexpr.c 2017-02-21 13:49:06.530261975 +0100 @@ -2263,9 +2263,10 @@ cxx_eval_array_reference (const constexp nelts = cxx_eval_constant_expression (ctx, nelts, false, non_constant_p, overflow_p); VERIFY_CONSTANT (nelts); - if (lval - ? !tree_int_cst_le (index, nelts) - : !tree_int_cst_lt (index, nelts)) + if ((lval + ? !tree_int_cst_le (index, nelts) + : !tree_int_cst_lt (index, nelts)) + || tree_int_cst_sgn (index) < 0) { diag_array_subscript (ctx, ary, index); *non_constant_p = true; --- gcc/testsuite/g++.dg/cpp1y/constexpr-79655.C.jj 2017-02-21 14:14:37.245395108 +0100 +++ gcc/testsuite/g++.dg/cpp1y/constexpr-79655.C 2017-02-21 14:14:07.000000000 +0100 @@ -0,0 +1,18 @@ +// PR c++/79655 +// { dg-do compile { target c++14 } } + +constexpr int +foo (int x, int y) +{ + int a[6] = { 1, 2, 3, 4, 5, 6 }; + a[x] = 0; + return a[y]; +} + +constexpr int b = foo (0, -1); // { dg-error "is outside the bounds" } +constexpr int c = foo (0, 6); // { dg-error "is outside the bounds" } +constexpr int d = foo (6, 0); // { dg-error "is outside the bounds" } +constexpr int e = foo (-1, 0); // { dg-error "is outside the bounds" } +static_assert (foo (5, 5) == 0, ""); +static_assert (foo (4, 5) == 6, ""); +static_assert (foo (5, 4) == 5, ""); Jakub
