Which data structure in a compiler is used for managing information about variables and their attributes?

The grammar $$S \to aSa\,|\,\,bS\,|\,\,c$$ is

The program below uses six temporary variables a, b, c, d, e, f.

a = 1 
b = 10 
c = 20 
d = a + b 
e = c + d 
f = c + e 
b = c + e 
e = b + f 
d = 5 + e 
return d + f

Assuming that all operations take their operands from registers, what is the minimum number of registers needed to execute this program without spilling?

Which languages necessarily need heap allocation in the runtime environment?