Using shorthand *= leads to unexpected result?

[Saurabh Das via Digitalmars-d-learn]

On Sunday, 15 May 2016 at 13:25:42 UTC, Michael wrote:
> Well I'm pretty sure the code was working just fine earlier in 
> the week at the office, but running the code at home with the 
> newest version of DMD started producing these odd results.

Typing this function into asm.dlang.org shows a minor difference 
in the assembly generated:

auto f1(double d1)
{
   d1 *= -1.0;
   return d1;
}

With DMD 2.070.2:
pure nothrow @nogc @safe double example.f1(double):
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x10,%rsp
  movsd  %xmm0,-0x8(%rbp)
  xorb   $0x80,-0x1(%rbp)
  rex.W movsd  -0x8(%rbp),%xmm0
  leaveq
  retq
  nopl   0x0(%rax)

With DMD 2.071.0:
pure nothrow @nogc @safe double example.f1(double):
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x10,%rsp
  movsd  %xmm0,-0x8(%rbp)
  xorb   $0x80,-0x8(%rbp)
  rex.W movsd  -0x8(%rbp),%xmm0
  leaveq
  retq
  nopl   0x0(%rax)

The xorb line is different and I conjecture that it is causing 
the bug. I have never used floating-point assembly instructions, 
so I cannot understand what the logic is here. I'll read up and 
try to interpret to confirm.

Hope this helps.