[Bug c++/86497] New: Regression for x!=x

[no...@turm-lahnstein.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86497

            Bug ID: 86497
           Summary: Regression for x!=x
           Product: gcc
           Version: 8.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: no...@turm-lahnstein.de
  Target Milestone: ---

When compiling

bool is_nan1(double x){
    return x!=x;
}

with g++-8.1  -O3 the resulting assembler (https://godbolt.org/g/BBFM3Q) is 

_Z7is_nan1d:
  ucomisd %xmm0, %xmm0
  movl $1, %edx
  setne %al
  cmovp %edx, %eax
  ret

However, for version 7.3 the result was (https://godbolt.org/g/tR69jf) better:

_Z7is_nan1d:
  ucomisd %xmm0, %xmm0
  setp %al
  ret

Also for 8.1 -Os is the assembler somewhat strange:

_Z7is_nan1d:
  ucomisd %xmm0, %xmm0
  movb $1, %al
  jp .L2
  setne %al