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c++: more mce_false folding from cp_fully_fold_init [PR108243]

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We should also fold the overall initializer passed to cp_fully_fold_init
with mce_false, which allows folding of the copy-initialization of
'a1' in the below testcase (the initializer here is an AGGR_INIT_EXPR).

Unfortunately this doesn't help with direct- or default-initialization
because we don't call cp_fully_fold_init in that case, and even if we
did the initializer in that case is expressed as a bare CALL_EXPR
instead of an AGGR_INIT_EXPR, which cp_fully_fold_init can't really
fold.

	PR c++/108243
	PR c++/97553

gcc/cp/ChangeLog:

	* cp-gimplify.cc (cp_fully_fold): Add an internal overload that
	additionally takes and propagate an mce_value parameter, and
	define the existing public overload in terms of it.
	(cp_fully_fold_init): Pass mce_false to cp_fully_fold.

gcc/testsuite/ChangeLog:

	* g++.dg/opt/is_constant_evaluated3.C: New test.
This commit is contained in:
Patrick Palka 2023-03-02 14:04:50 -05:00
parent cbaa1d9c21
commit 5425159d17
2 changed files with 37 additions and 5 deletions
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19
gcc/cp/cp-gimplify.cc
View File

@ -2449,8 +2449,8 @@ cp_fold_rvalue (tree x)
/* Perform folding on expression X. */
tree
cp_fully_fold (tree x)
static tree
cp_fully_fold (tree x, mce_value manifestly_const_eval)
{
if (processing_template_decl)
return x;
@ -2458,7 +2458,7 @@ cp_fully_fold (tree x)
have to call both. */
if (cxx_dialect >= cxx11)
{
x = maybe_constant_value (x);
x = maybe_constant_value (x, /*decl=*/NULL_TREE, manifestly_const_eval);
/* Sometimes we are given a CONSTRUCTOR but the call above wraps it into
a TARGET_EXPR; undo that here. */
if (TREE_CODE (x) == TARGET_EXPR)
@ -2468,7 +2468,16 @@ cp_fully_fold (tree x)
&& TREE_TYPE (TREE_OPERAND (x, 0)) == TREE_TYPE (x))
x = TREE_OPERAND (x, 0);
}
return cp_fold_rvalue (x);
fold_flags_t flags = ff_none;
if (manifestly_const_eval == mce_false)
flags |= ff_mce_false;
return cp_fold_rvalue (x, flags);
}
tree
cp_fully_fold (tree x)
{
return cp_fully_fold (x, mce_unknown);
}
/* Likewise, but also fold recursively, which cp_fully_fold doesn't perform
@ -2479,7 +2488,7 @@ cp_fully_fold_init (tree x)
{
if (processing_template_decl)
return x;
x = cp_fully_fold (x);
x = cp_fully_fold (x, mce_false);
cp_fold_data data (ff_mce_false);
cp_walk_tree (&x, cp_fold_r, &data, NULL);
return x;

23
gcc/testsuite/g++.dg/opt/is_constant_evaluated3.C Normal file
View File

@ -0,0 +1,23 @@
// PR c++/108243
// { dg-do compile { target c++11 } }
// { dg-additional-options "-O -fdump-tree-original" }
struct A {
constexpr A(int n) : n(n), m(__builtin_is_constant_evaluated()) { }
constexpr A() : A(42) { }
int n, m;
};
int main() {
A a1 = {42};
A a2{42};
A a3(42);
A a4;
A a5{};
}
// { dg-final { scan-tree-dump "a1 = {\\.n=42, \\.m=0}" "original" } }
// { dg-final { scan-tree-dump "a2 = {\\.n=42, \\.m=0}" "original" { xfail *-*-* } } }
// { dg-final { scan-tree-dump "a3 = {\\.n=42, \\.m=0}" "original" { xfail *-*-* } } }
// { dg-final { scan-tree-dump "a4 = {\\.n=42, \\.m=0}" "original" { xfail *-*-* } } }
// { dg-final { scan-tree-dump "a5 = {\\.n=42, \\.m=0}" "original" { xfail *-*-* } } }