https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85281
Bug ID: 85281 Summary: [8 Regression] Assembler messages: Error: operand size mismatch for `vpbroadcastb' with -mavx512bw -masm=intel 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 43875 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43875&action=edit reduced testcase Compiler output: $ x86_64-pc-linux-gnu-gcc -O -mavx512bw -masm=intel -w testcase.c -save-temps testcase.s: Assembler messages: testcase.s:32: Error: operand size mismatch for `vpbroadcastb' The failing instruction is: ... vpbroadcastb zmm0{k2}, XMMWORD PTR [rsp+48] ... which is mixing zmm0 and XMMWORD. This compiles fine with att syntax: ... vpbroadcastb 48(%rsp), %zmm0{%k2} ... The gcc I am using is patched with the fix for PR85177#c1 7-branch is fine on this testcase, but it generates very different (inferior in my eyes) code. $ 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)