AMD64 vs EMT64, compilation & execution

[Banibrata Dutta]

Hi,

AFAIU (from the Wikipedia definition of EMT64 / EM64T or that of
x86_64), there are some small instruction level and behavioural
differences, between the AMD implementation of the 64-bit technology
and Intel implementation of the it.

My question in the scope of GCC is, is it guaranteed that Code
compiled and linked on AMD64 environment (s.a. AMD Opteron) will run
flawlessly in EMT64 environment (s.a. PentiumD w/EMT64), and
vice-versa ? Does GCC always guarantee that the processor specific
optimization is not used, but only instructions / features common to
both AMD64/EMT64 are used in the final binaries ?

If there is an authoratative documentation of this fact somewhere,
even in form of a mail describing this from a senior developer /
committer for GCC, it'd be wonderful.

thanks & regards,
Banibrata Dutta