Can a C compiler generate an executable 64-bits where pointers are 32-bits?

Question

Most programs fits well on <4GB address space but needs to use new features just available on x64 architecture.

Are there compilers/platforms where I can use x64 regi

Answer 1

On x86, no. On other processors, such as PowerPC it is quite common - 64 bit registers and instructions are available in 32 bit mode, whereas with x86 it tends to be "all or nothing".