https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85328
Bug ID: 85328
Summary: accessing ymm16 with non-avx512 instruction form
Product: gcc
Version: 8.0.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: zsojka at seznam dot cz
Target Milestone: ---
Created attachment 43902
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43902&action=edit
reduced testcase
Compiler output:
$ x86_64-pc-linux-gnu-gcc -O3 -fno-caller-saves -mavx512f testcase.c
/tmp/ccNXhuu3.s: Assembler messages:
/tmp/ccNXhuu3.s:418: Error: unsupported instruction `vpand'
The failing instruction is:
...
vpand %ymm16, %ymm1, %ymm1
...
I tried both most recent GNU as and NASM (both from most recent GIT), but
neither accept this form. Accessing ymm >= 16 is allowed only with the
EVEX-prefixed VPANDD or VPANDQ.
I am really not an expert in AVX512 instruction encoding, but gcc seems to be
wrong here according to the assemblers I tested and Intel's SDM vol.2:
only vpandd/vpandq are using the EVEX prefix, and you can use ymm >= 16 only
with the EVEX prefix.
(this can be generalized to other instructions, such as vpor, and maybe to
other registers, such as xmm/zmm)
$ x86_64-pc-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=/repo/gcc-trunk/binary-latest-amd64/bin/x86_64-pc-linux-gnu-gcc
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-259207-checking-yes-rtl-df-extra-nobootstrap-pr85177-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/8.0.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++
--enable-valgrind-annotations --disable-nls --enable-checking=yes,rtl,df,extra
--disable-bootstrap --with-cloog --with-ppl --with-isl
--build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu
--target=x86_64-pc-linux-gnu --with-ld=/usr/bin/x86_64-pc-linux-gnu-ld
--with-as=/usr/bin/x86_64-pc-linux-gnu-as --disable-libstdcxx-pch
--prefix=/repo/gcc-trunk//binary-trunk-259207-checking-yes-rtl-df-extra-nobootstrap-pr85177-amd64
Thread model: posix
gcc version 8.0.1 20180407 (experimental) (GCC)
