From: Jason Merrill Date: Tue, 19 Feb 2019 01:01:50 +0000 (-0500) Subject: PR c++/89336 - multiple stores in constexpr stmt. X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=e8b3c1bc3ba22dcf59b9c743f11d4cb2bc5d7792;p=gcc.git PR c++/89336 - multiple stores in constexpr stmt. If we evaluate the RHS in the context of the LHS, that evaluation might change the LHS in ways that mess with being able to store the value later. So for assignment or scalar values, evaluate the RHS first. * constexpr.c (cxx_eval_store_expression): Preevaluate scalar or assigned value. From-SVN: r269003 --- diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog index 33a1ca24c9f..5d909ef62ec 100644 --- a/gcc/cp/ChangeLog +++ b/gcc/cp/ChangeLog @@ -1,5 +1,9 @@ 2019-02-18 Jason Merrill + PR c++/89336 - multiple stores in constexpr stmt. + * constexpr.c (cxx_eval_store_expression): Preevaluate scalar or + assigned value. + * pt.c (check_explicit_specialization): If the declarator is a template-id, only check whether the arguments are dependent. diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c index d946a797999..d413c6b9b27 100644 --- a/gcc/cp/constexpr.c +++ b/gcc/cp/constexpr.c @@ -3634,6 +3634,18 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t, maybe_simplify_trivial_copy (target, init); tree type = TREE_TYPE (target); + bool preeval = SCALAR_TYPE_P (type) || TREE_CODE (t) == MODIFY_EXPR; + if (preeval) + { + /* Evaluate the value to be stored without knowing what object it will be + stored in, so that any side-effects happen first. */ + if (!SCALAR_TYPE_P (type)) + new_ctx.ctor = new_ctx.object = NULL_TREE; + init = cxx_eval_constant_expression (&new_ctx, init, false, + non_constant_p, overflow_p); + if (*non_constant_p) + return t; + } target = cxx_eval_constant_expression (ctx, target, true, non_constant_p, overflow_p); @@ -3834,7 +3846,7 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t, } release_tree_vector (refs); - if (AGGREGATE_TYPE_P (type) || VECTOR_TYPE_P (type)) + if (!preeval) { /* Create a new CONSTRUCTOR in case evaluation of the initializer wants to modify it. */ @@ -3843,21 +3855,20 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t, *valp = build_constructor (type, NULL); CONSTRUCTOR_NO_CLEARING (*valp) = no_zero_init; } - else if (TREE_CODE (*valp) == PTRMEM_CST) - *valp = cplus_expand_constant (*valp); new_ctx.ctor = *valp; new_ctx.object = target; + init = cxx_eval_constant_expression (&new_ctx, init, false, + non_constant_p, overflow_p); + if (target == object) + /* The hash table might have moved since the get earlier. */ + valp = ctx->values->get (object); } - init = cxx_eval_constant_expression (&new_ctx, init, false, - non_constant_p, overflow_p); /* Don't share a CONSTRUCTOR that might be changed later. */ init = unshare_constructor (init); - if (target == object) - /* The hash table might have moved since the get earlier. */ - valp = ctx->values->get (object); - if (TREE_CODE (init) == CONSTRUCTOR) + if (*valp && TREE_CODE (*valp) == CONSTRUCTOR + && TREE_CODE (init) == CONSTRUCTOR) { /* An outer ctx->ctor might be pointing to *valp, so replace its contents. */ diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-89336-1.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-89336-1.C new file mode 100644 index 00000000000..93fe16551a1 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-89336-1.C @@ -0,0 +1,35 @@ +// PR c++/89336 +// { dg-do compile { target c++14 } } + +template struct A { + T a[N]; + constexpr T &operator[] (int x) { return a[x]; } + constexpr const T &operator[] (int x) const { return a[x]; } +}; + +constexpr A +foo () +{ + A r{}; + for (int i = 0; i < 6; ++i) + r[i + 8] = r[i] = i + 1; + return r; +} + +constexpr auto x = foo (); +static_assert (x[0] == 1, ""); +static_assert (x[1] == 2, ""); +static_assert (x[2] == 3, ""); +static_assert (x[3] == 4, ""); +static_assert (x[4] == 5, ""); +static_assert (x[5] == 6, ""); +static_assert (x[6] == 0, ""); +static_assert (x[7] == 0, ""); +static_assert (x[8] == 1, ""); +static_assert (x[9] == 2, ""); +static_assert (x[10] == 3, ""); +static_assert (x[11] == 4, ""); +static_assert (x[12] == 5, ""); +static_assert (x[13] == 6, ""); +static_assert (x[14] == 0, ""); +static_assert (x[15] == 0, ""); diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-89336-2.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-89336-2.C new file mode 100644 index 00000000000..69889ffb2b4 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-89336-2.C @@ -0,0 +1,56 @@ +// PR c++/89336 +// { dg-do compile { target c++14 } } + +constexpr int +foo () +{ + int a[16] = {}; + int r = 0; + a[15] = a[14] = a[13] = a[12] = a[11] = a[10] = a[9] = a[8] + = a[7] = a[6] = a[5] = a[4] = a[3] = a[2] = a[1] = a[0] = 5; + for (int i = 0; i < 16; ++i) + r += a[i]; + return r; +} + +static_assert (foo () == 16 * 5, ""); + +struct A { int a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p; }; + +constexpr int +bar () +{ + A a {}; + a.p = a.o = a.n = a.m = a.l = a.k = a.j = a.i + = a.h = a.g = a.f = a.e = a.d = a.c = a.b = a.a = 8; + return a.a + a.b + a.c + a.d + a.e + a.f + a.g + a.h + + a.i + a.j + a.k + a.l + a.m + a.n + a.o + a.p; +} + +static_assert (bar () == 16 * 8, ""); + +constexpr int +baz () +{ + int a[16] = {}; + int r = 0; + a[0] = a[1] = a[2] = a[3] = a[4] = a[5] = a[6] = a[7] + = a[8] = a[9] = a[10] = a[11] = a[12] = a[13] = a[14] = a[15] = 7; + for (int i = 0; i < 16; ++i) + r += a[i]; + return r; +} + +static_assert (baz () == 16 * 7, ""); + +constexpr int +qux () +{ + A a {}; + a.a = a.b = a.c = a.d = a.e = a.f = a.g = a.h + = a.i = a.j = a.k = a.l = a.m = a.n = a.o = a.p = 6; + return a.a + a.b + a.c + a.d + a.e + a.f + a.g + a.h + + a.i + a.j + a.k + a.l + a.m + a.n + a.o + a.p; +} + +static_assert (qux () == 16 * 6, "");