[Bug inline-asm/98847] New: Miscompilation with c++17, templates, and register keyword

["programmerjake at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98847

            Bug ID: 98847
           Summary: Miscompilation with c++17, templates, and register
                    keyword
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: inline-asm
          Assignee: unassigned at gcc dot gnu.org
          Reporter: programmerjake at gmail dot com
  Target Milestone: ---
              Host: x86_64-linux-gnu
            Target: x86_64-linux-gnu

In:
https://gcc.godbolt.org/z/49xoKP

With the following code:

template <typename T = void>
int template_get_edx() {
    register int edx asm("edx");
    asm("movl $1234, %%edx\n\t# reg=%0" : "=r"(edx));
    return edx;
}

template int template_get_edx<void>();

With: -O -Wall -std=c++17

Miscompiles, allocating %eax to the C++-level edx variable.

It's possible the C++ frontend is removing the register keyword before
finishing parsing since it also incorrectly warns here (bug #98846)

produces:
_Z16template_get_edxIvEiv:
.LFB1:
        .file 1 "./example.cpp"
        .loc 1 2 5 view -0
        .cfi_startproc
        .loc 1 4 5 is_stmt 0 view .LVU1
#APP
# 4 "./example.cpp" 1
        movl $1234, %edx
        # reg=%eax
# 0 "" 2
.LVL0:
        .loc 1 6 1 view .LVU2
#NO_APP
        ret