[llvm-bugs] [Bug 39895] New: Error: unknown token in expression using inline asm

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https://bugs.llvm.org/show_bug.cgi?id=39895

            Bug ID: 39895
           Summary: Error: unknown token in expression using inline asm
           Product: clang
           Version: 7.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: noloader at gmail.com
                CC: llvm-bugs at lists.llvm.org, neeilans at live.com,
                    richard-llvm at metafoo.co.uk

We have about 8K lines of inline assembly written to accommodate GCC and MSVC.
Clang is currently disabled but we would like to enable it.

The inline assembly in the production code is hidden behind macros. The body is
Intel and the assembler template is AT&T. GCC sees both while MSVC only sees
the Intel body without the other adornments.

Clang is having trouble with it. It looks like Clang handles the noprefix OK
because "xor rsi, rsi" does not cause an error. However, the positional
arguments are giving it trouble.

$ cat TestPrograms/test_mixed_asm.cxx
#include <cstddef>
int main(int argc, char* argv[])
{
        size_t ret = 1, N = 0;
        asm __volatile__
        (
                ".intel_syntax   noprefix ;\n"
                "xor rsi, rsi    ;\n"
                "neg %1          ;\n"
                "inc %1          ;\n"
                "push %1         ;\n"
                "pop rax         ;\n"
                ".att_syntax     prefix ;\n"
                : "=a" (ret) : "c" (N) : "%rsi"
        );
        return (int)ret;
}

Compiling with GCC on Linux is OK:

$ g++ TestPrograms/test_mixed_asm.cxx

But Clang on Linux is having trouble:

$ clang++ TestPrograms/test_mixed_asm.cxx
TestPrograms/test_mixed_asm.cxx:11:4: error: unknown token in expression
                "neg %1          ;\n"
                 ^
<inline asm>:3:5: note: instantiated into assembly here
neg %rcx          ;
    ^
TestPrograms/test_mixed_asm.cxx:12:4: error: unknown token in expression
                "inc %1          ;\n"
                 ^
<inline asm>:4:5: note: instantiated into assembly here
inc %rcx          ;
    ^
TestPrograms/test_mixed_asm.cxx:13:4: error: unknown token in expression
                "push %1         ;\n"
                 ^
<inline asm>:5:6: note: instantiated into assembly here
push %rcx         ;
     ^
3 errors generated.

And:

$ clang++ --version
clang version 6.0.1 (tags/RELEASE_601/final)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /bin

Jumping over to MacPorts for Clang 7:

$ /opt/local/bin/clang++-mp-7.0 TestPrograms/test_mixed_asm.cxx
TestPrograms/test_mixed_asm.cxx:11:4: error: unknown token in expression
                "neg %1          ;\n"
                 ^
<inline asm>:3:5: note: instantiated into assembly here
neg %rcx          ;
    ^
TestPrograms/test_mixed_asm.cxx:12:4: error: unknown token in expression
                "inc %1          ;\n"
                 ^
<inline asm>:4:5: note: instantiated into assembly here
inc %rcx          ;
    ^
TestPrograms/test_mixed_asm.cxx:13:4: error: unknown token in expression
                "push %1         ;\n"
                 ^
<inline asm>:5:6: note: instantiated into assembly here
push %rcx         ;
     ^
3 errors generated.

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