I'm seeing an ICE from MIPS with MSA enabled when attempting to use __builtin_convertvector to convert a vector of 8 unsigned 8-bit integers to 8 unsigned 16-bit integers.

Here is a reduced test case, courtesy of C-Reduce:


typedef char a;
typedef short b;
typedef struct {
  a c __attribute__((__vector_size__(8)));
} d;
d e;
void f() {
  b g __attribute__((__vector_size__(16))) (
      __builtin_convertvector(e.c, __typeof__(g)));
}


$ mips64el-linux-gnuabi64-g++-10 -march=loongson3a -mmsa -c -o test.o test.c
during RTL pass: expand
test.c: In function 'void f()':
test.c:8:5: internal compiler error: in mips_expand_vec_unpack, at config/mips/mips.c:21757
    8 |   b g __attribute__((__vector_size__(16))) (
      |     ^
0x7fed0d1f9d09 __libc_start_main
	../csu/libc-start.c:308
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <file:///usr/share/doc/gcc-10/README.Bugs> for instructions.


This is with GCC 10.2.1-6 from Debian:

$ mips64el-linux-gnuabi64-g++-10 --version                                  
mips64el-linux-gnuabi64-g++-10 (Debian 10.2.1-6) 10.2.1 20210110
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


Original code is at https://github.com/simd-everywhere/simde/blob/7d0e2aca9458f760d7196b94bfdcf83b2178ea24/simde/x86/sse.h#L1046, SIMDE_CONVERT_VECTOR_ is defined at https://github.com/simd-everywhere/simde/blob/7d0e2aca9458f760d7196b94bfdcf83b2178ea24/simde/simde-common.h#L292-L296