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c++: Fix non-constant TARGET_EXPR constexpr handing [PR93998]

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We ICE on the following testcase since I've added the SAVE_EXPR-like
constexpr handling where the TARGET_EXPR initializer (and cleanup) is
evaluated only once (because it might have side-effects like new or delete
expressions in it).
The problem is if the TARGET_EXPR (but I guess in theory SAVE_EXPR too)
initializer is *non_constant_p.  We still remember the result, but already
not that it is *non_constant_p.  Normally that wouldn't be a big problem,
if something is *non_constant_p, we only or into it and so the whole
expression will be non-constant too.  Except in the builtins handling,
we try to evaluate the arguments with non_constant_p pointing into a dummy1
bool which we ignore.  This is because some builtins might fold into a
constant even if they don't have a constexpr argument.  Unfortunately if
we evaluate the TARGET_EXPR first in the argument of such a builtin and then
once again, we don't set *non_constant_p.

So, either we don't remember the TARGET_EXPR/SAVE_EXPR result if it wasn't
constant, like the following patch does, or we could remember it, but in
some way that would make it clear that it is non-constant (e.g. by
pushing into the global->values SAVE_EXPR, SAVE_EXPR entry and perhaps
for TARGET_EXPR don't remember it on TARGET_EXPR_SLOT, but the TARGET_EXPR
itself and similarly push TARGET_EXPR, TARGET_EXPR and if we see those
after the lookup, diagnose + set *non_constant_p.  Or we could perhaps
during the builtin argument evaluation push expressions into a different
save_expr vec and undo them afterwards.

2020-03-03  Jakub Jelinek  <jakub@redhat.com>

	PR c++/93998
	* constexpr.c (cxx_eval_constant_expression)
	<case TARGET_EXPR, case SAVE_EXPR>: Don't record anything if
	*non_constant_p is true.

	* g++.dg/ext/pr93998.C: New test.
This commit is contained in:
Jakub Jelinek 2020-03-03 19:49:12 +01:00
parent 6b9ce2b4eb
commit 0e0ffbfc23
4 changed files with 33 additions and 4 deletions
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9
gcc/cp/ChangeLog
View File

@ -1,4 +1,11 @@
2020-03-03 Jun Ma <JunMa@linux.alibaba.com>
2020-03-03 Jakub Jelinek <jakub@redhat.com>
PR c++/93998
* constexpr.c (cxx_eval_constant_expression)
<case TARGET_EXPR, case SAVE_EXPR>: Don't record anything if
*non_constant_p is true.
2020-03-03 Jun Ma <JunMa@linux.alibaba.com>
* coroutines.cc (finish_co_await_expr): Build co_await_expr
with unknown_type_node.

9
gcc/cp/constexpr.c
View File

@ -5474,9 +5474,10 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
r = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 1),
false,
non_constant_p, overflow_p);
if (!*non_constant_p)
/* Adjust the type of the result to the type of the temporary. */
r = adjust_temp_type (TREE_TYPE (t), r);
if (*non_constant_p)
break;
/* Adjust the type of the result to the type of the temporary. */
r = adjust_temp_type (TREE_TYPE (t), r);
if (TARGET_EXPR_CLEANUP (t) && !CLEANUP_EH_ONLY (t))
ctx->global->cleanups->safe_push (TARGET_EXPR_CLEANUP (t));
r = unshare_constructor (r);
@ -5528,6 +5529,8 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
{
r = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 0), false,
non_constant_p, overflow_p);
if (*non_constant_p)
break;
ctx->global->values.put (t, r);
if (ctx->save_exprs)
ctx->save_exprs->safe_push (t);

5
gcc/testsuite/ChangeLog
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@ -1,3 +1,8 @@
2020-03-03 Jakub Jelinek <jakub@redhat.com>
PR c++/93998
* g++.dg/ext/pr93998.C: New test.
2020-03-03 Dennis Zhang <dennis.zhang@arm.com>
* gcc.target/arm/simd/bf16_cvt_1.c: New test.

14
gcc/testsuite/g++.dg/ext/pr93998.C Normal file
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@ -0,0 +1,14 @@
// PR c++/93998
// { dg-do compile { target c++11 } }
struct C
{
constexpr bool operator== (C x) const noexcept { return v == x.v; }
int v;
};
int
foo (const C a, const C b, bool c)
{
return __builtin_expect (!!(a == b || c), 1) ? 0 : 1;
}