Register allocation is the most important optimization performed by the compiler because accessing a register is much faster than accessing even the cache.
Instruction scheduling is also important..
Allocation ensures that code will fit the target machine's reg. set at each instruction.
Maps an allocated name set to the physical register set of the target machine.
Assumes allocation has been done so that code will fit into the set of physical registers.Jan 24, 2022.
Register allocation can happen over a basic block (local register allocation), over a whole function/procedure (global register allocation), or across function boundaries traversed via call-graph (interprocedural register allocation)..
The advantage is registers can be accessed quickly.
The disadvantage is that the compiler does not need to honor the request to use a register.
You will not know unless you look at the assembly code.
If you absolutely need to use a register, use a block of assembly code in your program to do the processing..
If the compiler runs out of appropriate registers, it frees a register by moving its contents to memory.
If you define too many objects as register variables, you limit the number of registers the compiler has for temporary expression results.
This limit causes excessive movement of register contents to memory..
Register allocation is determining which values in a program will reside in registers, and which will spill.
Register assignment is determining which particular register each value will reside in..
Register allocation consists therefore of choosing where to store the variables at runtime, i.e. inside or outside registers.
If the variable is to be stored in registers, then the allocator needs to determine in which register(s) this variable will be stored..
Register allocation consists therefore of choosing where to store the variables at runtime, i.e. inside or outside registers.
If the variable is to be stored in registers, then the allocator needs to determine in which register(s) this variable will be stored..
Register allocation is interpreted as a graph coloring problem .
Nodes represent live range of the variable.
Edges represent the connection between two live ranges .
Assigning color to the nodes such that no two adjacent nodes have same color .Dec 29, 2020.
Register allocation determines which registers are used to hold the values in the program.
From: High-Performance Embedded Computing (Second Edition), 2014..
If the compiler runs out of appropriate registers, it frees a register by moving its contents to memory.
If you define too many objects as register variables, you limit the number of registers the compiler has for temporary expression results.
This limit causes excessive movement of register contents to memory..
In addition, it speeds up the execution time of the compiled program; therefore, efficient compilers aim at assigning as many variables to registers as they can.
Generally, most register allocators assign every variable to main memory or a central processing unit (CPU) register.Feb 3, 2015.
Let register allocator figure out if it can assign the same register to two temps! Then the copy can go away.
And we don't have to worry about register pressure.
If we have “x := y” and x and y have no edge in the interference graph, we might be able to assign them the same color.
But coalescing may make a uncolorable! .
Registers are available in small size up to few hundred Kb .Thus it is necessary to use minimum number of registers for variable allocation .
There are three popular Register allocation algorithms .
These are explained as following below.
Register allocation can be done in either the intermediate code generation phase or the machine code generation phase.
Register allocation during intermediate code generation has the advantage that the register allocator can be used for several target machines by parameterizing with the available set of registers.
In compiler optimization, register allocation is the process of assigning local automatic variables and expression results to a limited number of processor registers .
CPU architecture feature to improve performance
