compiler construction - register allocation for x86 -

i attempting simple register allocation x86. using linear register allocator have few questions on simple things not finding information about.

int main() {     int a, b, c;     = 10;     b = 20;     c = 2;     = + b;     b = b * 5;     c = c * b + a;     return c; } 

for simple code, ignoring constant propagation, g++ & msvc generate similar code pushes temporaries on stack , uses eax, ebx etc alu ops. clang generates following code o0.

main:                                   # @main     movl    $0, -4(%rsp)     movl    $10, -8(%rsp)     movl    $20, -12(%rsp)     movl    $2, -16(%rsp)     movl    -8(%rsp), %eax     addl    -12(%rsp), %eax     movl    %eax, -8(%rsp)     imull   $5, -12(%rsp), %eax     movl    %eax, -12(%rsp)     movl    -16(%rsp), %eax     imull   -12(%rsp), %eax     addl    -8(%rsp), %eax     movl    %eax, -16(%rsp)     movl    -16(%rsp), %eax     ret 

as evident, temporaries on stack. question based on same thing. at point, should in eax/ebx etc used in add/mul/div operations etc have lifetime more 1 instruction. is, should live range interval have value stored in these registers or should evicted register allocation done , values pushed temporaries ?

or can use of these registers till next alu instruction encountered , lazy push stack when necessary?