[Bug c++/65966] New: "sorry, unimplemented: unexpected AST of kind try_block" when initializing a 2D array

["lhyatt at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65966

            Bug ID: 65966
           Summary: "sorry, unimplemented: unexpected AST of kind
                    try_block" when initializing a 2D array
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lhyatt at gmail dot com
  Target Milestone: ---

This fails to compile with gcc 5.1, is fine with 4.9:

========
struct A {
    A();
    ~A();
};

struct B {
    A a{};
};

struct C {
    B array[100][100];
} c;
=========

$ g++ -v -c -std=c++14 t.cpp
Using built-in specs.
COLLECT_GCC=g++
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-5.1.0/configure --prefix=/usr/local/gcc-5.1.0
--with-tune=westmere --with-arch=nehalem
Thread model: posix
gcc version 5.1.0 (GCC)
COLLECT_GCC_OPTIONS='-v' '-c' '-std=c++14' '-shared-libgcc' '-mtune=westmere'
'-march=nehalem'
 /usr/local/gcc-5.1.0/libexec/gcc/x86_64-unknown-linux-gnu/5.1.0/cc1plus -quiet
-v -D_GNU_SOURCE t.cpp -quiet -dumpbase t.cpp -mtune=westmere -march=nehalem
-auxbase t -std=c++14 -version -o /tmp/ccmhY1ZH.s
GNU C++14 (GCC) version 5.1.0 (x86_64-unknown-linux-gnu)
        compiled by GNU C version 5.1.0, GMP version 4.3.2, MPFR version
2.4.2-p1, MPC version 0.8.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring nonexistent directory
"/usr/local/gcc-5.1.0/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../x86_64-unknown-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:

/usr/local/gcc-5.1.0/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../include/c++/5.1.0

/usr/local/gcc-5.1.0/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../include/c++/5.1.0/x86_64-unknown-linux-gnu

/usr/local/gcc-5.1.0/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/../../../../include/c++/5.1.0/backward
 /usr/local/gcc-5.1.0/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/include
 /usr/local/include
 /usr/local/gcc-5.1.0/include
 /usr/local/gcc-5.1.0/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/include-fixed
 /usr/include
End of search list.
GNU C++14 (GCC) version 5.1.0 (x86_64-unknown-linux-gnu)
        compiled by GNU C version 5.1.0, GMP version 4.3.2, MPFR version
2.4.2-p1, MPC version 0.8.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 2a9de20833bb0c7b695acd3b2e90df62
t.cpp: In constructor 'constexpr C::C()':
t.cpp:10:8: sorry, unimplemented: unexpected AST of kind try_block
 struct C {
        ^
t.cpp:10: confused by earlier errors, bailing out


Generally all the features in the testcase must be present (need a 2d array,
not 1d; need to explicitly put the constructor + destructor for class A; need
class B to have the NSDMI for its "a" subobject) for the error to occur.

If I make the following small change to explicitly initialize the array in
class C:

========
struct A {
    A();
    ~A();
};

struct B {
    A a{};
};

struct C {
    B array[100][100] = {};
} c;
=========

then it compiles OK. However, in this case there seems to be some sort of other
issue, instead of a loop, it outputs 10000 individual instructions to
initialize the array:

.LEHB0:
        call    _ZN1AC1Ev
.LEHE0:
        leaq    1(%rbx), %rax
        movq    %rax, %rdi
.LEHB1:
        call    _ZN1AC1Ev
.LEHE1:
        leaq    2(%rbx), %rax
        movq    %rax, %rdi
.LEHB2:
        call    _ZN1AC1Ev
.LEHE2:
        leaq    3(%rbx), %rax
        movq    %rax, %rdi
.LEHB3:
        call    _ZN1AC1Ev
.LEHE3:
        leaq    4(%rbx), %rax
        movq    %rax, %rdi


... etc 10000 times.

We have a use case where we have a 100x100x100 3d array, and the compiler
spends hours generating these 1 millions instructions, whereas gcc 4.9 just
generated a reasonable loop right away.

Thank you...

-Lewis