Register WindowsOn the face of it,

Register Windows
On the face of it, the use of a large set of registers should decrease the need to access memory.The design task is to organize the registers in such a fashion that this goal is realized. Because most operand references are to local scalars, the obvious approach is to store these in registers, with perhaps a few registers reserved for global variables. The problem is that the definition of localchanges with each procedure call and return, operations that occur frequently. On every call, local variables must be saved from the registers into memory, so that the registers can be reused by the called program. Furthermore, parameters must be passed. On return, the variables of the parent program must be restored (loaded back into registers) and results must be passed back to the parent program. The solution is based on two other results reported in Section 13.1. First, a typical procedure employs only a few passed parameters and local variables (Table 13.4). Second, the depth of procedure activation fluctuates within a relatively narrow range (Figure 4.21). To exploit these properties, multiple small sets of registers are used, each assigned to a different procedure. A procedure call automatically switches the processor to use a different fixed-size window of registers, rather than saving registers in memory. Windows for adjacent procedures are overlapped to allow parameter passing. The concept is illustrated in Figure 13.1. At any time, only one window of registers is visible and is addressable as if it were the only set of registers (e.g., addresses 0 through N 1).The window is divided into three fixed-size areas. Parameter registers
hold parameters passed down from the procedure that called the current procedure and hold results to be passed back up. Local registers are used for local variables, as assigned by the compiler. Temporary registers are used to exchange parameters and results with the next lower level (procedure called by current procedure).The temporary registers at one level are physically the same as the parameter registers at the next

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Đăng ký WindowsOn the face of it, the use of a large set of registers should decrease the need to access memory.The design task is to organize the registers in such a fashion that this goal is realized. Because most operand references are to local scalars, the obvious approach is to store these in registers, with perhaps a few registers reserved for global variables. The problem is that the definition of localchanges with each procedure call and return, operations that occur frequently. On every call, local variables must be saved from the registers into memory, so that the registers can be reused by the called program. Furthermore, parameters must be passed. On return, the variables of the parent program must be restored (loaded back into registers) and results must be passed back to the parent program. The solution is based on two other results reported in Section 13.1. First, a typical procedure employs only a few passed parameters and local variables (Table 13.4). Second, the depth of procedure activation fluctuates within a relatively narrow range (Figure 4.21). To exploit these properties, multiple small sets of registers are used, each assigned to a different procedure. A procedure call automatically switches the processor to use a different fixed-size window of registers, rather than saving registers in memory. Windows for adjacent procedures are overlapped to allow parameter passing. The concept is illustrated in Figure 13.1. At any time, only one window of registers is visible and is addressable as if it were the only set of registers (e.g., addresses 0 through N 1).The window is divided into three fixed-size areas. Parameter registershold parameters passed down from the procedure that called the current procedure and hold results to be passed back up. Local registers are used for local variables, as assigned by the compiler. Temporary registers are used to exchange parameters and results with the next lower level (procedure called by current procedure).The temporary registers at one level are physically the same as the parameter registers at the next