The (invalid) testcase was causing an ICE because we were passing the result of array_type_nelts_top immediately into tree_int_cst_lt, but for VLAs, the result doesn't have to be a constant. Fixed by evaluating the bound of the array so that we're able to give a proper out-of-bounds diagnostics. And the VERIFY_CONSTANT should ensure that if the array bound couldn't be reduced to a constant, we bail out rather than evoke an ICE.
Bootstrapped/regtested on x86_64-linux, ok for trunk? 2016-01-26 Marek Polacek <pola...@redhat.com> PR c++/69496 * constexpr.c (cxx_eval_array_reference): Evaluate the number of elements of the array. * g++.dg/cpp1y/constexpr-vla1.C: New test. diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c index 6b0e5a8..6324e45 100644 --- gcc/cp/constexpr.c +++ gcc/cp/constexpr.c @@ -1855,7 +1855,12 @@ cxx_eval_array_reference (const constexpr_ctx *ctx, tree t, if (!found) { - if (tree_int_cst_lt (index, array_type_nelts_top (TREE_TYPE (ary)))) + tree nelts = array_type_nelts_top (TREE_TYPE (ary)); + /* For VLAs, the number of elements won't be an integer constant. */ + nelts = cxx_eval_constant_expression (ctx, nelts, false, non_constant_p, + overflow_p); + VERIFY_CONSTANT (nelts); + if (tree_int_cst_lt (index, nelts)) { if (TREE_CODE (ary) == CONSTRUCTOR && CONSTRUCTOR_NO_IMPLICIT_ZERO (ary)) diff --git gcc/testsuite/g++.dg/cpp1y/constexpr-vla1.C gcc/testsuite/g++.dg/cpp1y/constexpr-vla1.C index e69de29..a5615bb 100644 --- gcc/testsuite/g++.dg/cpp1y/constexpr-vla1.C +++ gcc/testsuite/g++.dg/cpp1y/constexpr-vla1.C @@ -0,0 +1,30 @@ +// PR c++/69496 +// { dg-do compile { target c++14 } } + +constexpr int +fn_ok (int n) +{ + __extension__ int a[n] = { }; + int z = 0; + + for (unsigned i = 0; i < sizeof (a) / sizeof (int); ++i) + z += a[i]; + + return z; +} + + +constexpr int +fn_not_ok (int n) +{ + __extension__ int a[n] = { }; + int z = 0; + + for (unsigned i = 0; i < sizeof (a); ++i) + z += a[i]; + + return z; +} + +constexpr int n1 = fn_ok (3); +constexpr int n2 = fn_not_ok (3); // { dg-error "array subscript out of bound" } Marek