Message ID | 20180416192843.GT8577@tucnak |
---|---|
State | New |
Headers | show |
Series | [C++] Fix constexpr handling of &x->y (PR c++/84463) | expand |
On Mon, Apr 16, 2018, 1:31 PM Jakub Jelinek <jakub@redhat.com> wrote: > On Mon, Apr 16, 2018 at 09:28:43PM +0200, Jakub Jelinek wrote: > > On the following new testcase we emit 2 different constexpr errors > > because of premature folding, where the PR44100 hack which is supposed > > to fold expressions like &((S *)0)->f or > > &((S *)24)->f folds all the &x->y expressions if x is TREE_CONSTANT > > into (some type)(x + cst) where what we were actually trying to access > > is lost. > > > > The following patch limits the offsetof-like expression hack to > expressions > > where maybe_constant_value of val's operand is INTEGER_CST, or e.g. > > a cast of INTEGER_CST to some pointer type. This way we don't regress > > e.g. init/struct2.C, but don't mess up with x is e.g. some constexpr > > variable initialized to address of something. Or should it avoid > > maybe_constant_value and just handle the literal INTEGER_CST and cast > > thereof? We wouldn't handle &((S *)(24 + 8))->f that way though... > > Or shall we move this folding to cp_fold instead of cp_build_addr_expr_1 > (while keeping it limited to INTEGER_CST pointers)? Yes, I think that would be better. >
--- gcc/cp/typeck.c.jj 2018-04-16 18:11:54.784378158 +0200 +++ gcc/cp/typeck.c 2018-04-16 21:03:15.674152875 +0200 @@ -5902,8 +5902,13 @@ cp_build_addr_expr_1 (tree arg, bool str && INDIRECT_REF_P (val) && TREE_CONSTANT (TREE_OPERAND (val, 0))) { - tree type = build_pointer_type (argtype); - return fold_convert (type, fold_offsetof_1 (arg)); + tree t = maybe_constant_value (TREE_OPERAND (val, 0)); + STRIP_NOPS (t); + if (TREE_CODE (t) == INTEGER_CST) + { + tree type = build_pointer_type (argtype); + return fold_convert (type, fold_offsetof_1 (arg)); + } } /* Handle complex lvalues (when permitted) --- gcc/testsuite/g++.dg/cpp0x/constexpr-nullptr-1.C.jj 2016-09-30 09:42:13.778446684 +0200 +++ gcc/testsuite/g++.dg/cpp0x/constexpr-nullptr-1.C 2018-04-16 21:13:06.057428435 +0200 @@ -6,7 +6,7 @@ // c++/67376 on gcc-patches for additional background. // { dg-do compile { target c++11 } } -// { dg-options "-fdelete-null-pointer-checks -fdump-tree-optimized" } +// { dg-options "-O1 -fdelete-null-pointer-checks -fdump-tree-optimized" } // Runtime assert. Used for potentially invalid expressions. #define RA(e) ((e) ? (void)0 : __builtin_abort ()) --- gcc/testsuite/g++.dg/cpp0x/constexpr-84463.C.jj 2018-04-16 21:02:16.282128997 +0200 +++ gcc/testsuite/g++.dg/cpp0x/constexpr-84463.C 2018-04-16 21:02:16.282128997 +0200 @@ -0,0 +1,22 @@ +// PR c++/84463 +// { dg-do compile { target c++11 } } + +struct S { int r; const unsigned char s[5]; }; +static constexpr S a[] = { { 0, "abcd" } }; +struct T { const unsigned char s[5]; }; +static constexpr T b[] = { { "abcd" } }; + +constexpr int +foo (const unsigned char *x) +{ + return x[0]; +} + +constexpr static const S *j = &a[0]; +constexpr static const int k = j->s[0]; +constexpr static int l = foo (a[0].s); +constexpr static int m = foo (j->s); +constexpr static const T *n = &b[0]; +constexpr static const int o = n->s[0]; +constexpr static int p = foo (b[0].s); +constexpr static int q = foo (n->s);