Yes, it does:
/* We need to decide which NOP sequence to use for 32bit and
64bit. When -mtune= is used:
1. For PROCESSOR_I386, PROCESSOR_I486, PROCESSOR_PENTIUM and
PROCESSOR_GENERIC32, f32_patt will be used.
2. For PROCESSOR_PENTIUMPRO, PROCESSOR_PENTIUM4, PROCESSOR_NOCONA,
PROCESSOR_CORE, PROCESSOR_CORE2, and PROCESSOR_GENERIC64,
alt_long_patt will be used.
3. For PROCESSOR_ATHLON, PROCESSOR_K6, PROCESSOR_K8 and
PROCESSOR_AMDFAM10, alt_short_patt will be used.
When -mtune= isn't used, alt_long_patt will be used if
cpu_arch_isa_flags has Cpu686. Otherwise, f32_patt will
be used.
"alt_long_patt" uses NOPL and its variants.
That is A TOTAL PIECE OF SH*T, and against gcc's own documentation.
"-mtune=x" is very much defined to be a performance _tuning_ option, not an "architectural" option.
Quite frankly, this is a gcc bug. Plain and simple.