c++: Fix up find_array_ctor_elt RAW_DATA_CST handling [PR118534]

This is the third bug discovered today with the
https://gcc.gnu.org/pipermail/gcc-patches/2025-January/673945.html
hack but then turned into proper testcases where embed-24.C FAILed
since introduction of optimized #embed support and the others when
optimizing large C++ initializers using RAW_DATA_CST.

find_array_ctor_elt already has RAW_DATA_CST support, but on the
following testcases it misses one case I've missed.
The CONSTRUCTORs in question went through the braced_list_to_string
optimization which can turn INTEGER_CST RAW_DATA_CST INTEGER_CST
into just larger RAW_DATA_CST covering even those 2 bytes around it
(if they appear there in the underlying RAW_DATA_OWNER).
With this optimization, RAW_DATA_CST can be the last CONSTRUCTOR_ELTS
elt in a CONSTRUCTOR, either the sole one or say preceeded by some
unrelated other elements.  Now, if RAW_DATA_CST is the only one or
if there are no RAW_DATA_CSTs earlier in CONSTRUCTOR_ELTS, we can
trigger a bug in find_array_ctor_elt.
It has a smart optimization for the very common case where
CONSTRUCTOR_ELTS have indexes and index of the last elt is equal
to CONSTRUCTOR_NELTS (ary) - 1, then obviously we know there are
no RAW_DATA_CSTs before it and the indexes just go from 0 to nelts-1,
so when we care about any of those earlier indexes, we can just return i;
and not worry about anything.
Except it uses if (i < end) return i; rather than if (i < end - 1) return i;
For the latter cases, i.e. anything before the last elt, we know there
are no surprises and return i; is right.  But for the if (i == end - 1)
case, return i; is only correct if the last elt is not RAW_DATA_CST, if it
is RAW_DATA_CST, we still need to split it, which is handled by the code
later in the function.  So, for that we need begin = end - 1, so that the
binary search will just care about that last element.

2025-01-18  Jakub Jelinek  <jakub@redhat.com>

	PR c++/118534
	* constexpr.cc (find_array_ctor_elt): Don't return i early if
	i == end - 1 and the last elt's value is RAW_DATA_CST.

	* g++.dg/cpp/embed-24.C: New test.
	* g++.dg/cpp1y/pr118534.C: New test.

0 files changed, 0 insertions, 0 deletions