将变量存储在CPU寄存器中 [英] Storing variables in CPU registers

问题描述

我已经读到CPU寄存器是有限的，并且该值也可以自动存储。

I have read that CPU registers are limited and the value can also get stored in auto.

如何确认变量是否存储在C语言的寄存器中？

How to confirm if the variable is stored in a register in C?

可以存储什么样的变量？

What kind of variables can be stored?

推荐答案

大多数编译器支持诸如 -S 或 / S 之类的标志，这些标志生成汇编语言输出。您可以检查这段代码，以查看编译器是否在给定点将给定变量存储在寄存器中。

Most compilers support a flag such as -S or /S that generates assembly-language output. You can inspect this code to see whether your compiler stores a given variable in a register at a given point.

没有保证可以放入寄存器的类型。实际上，一些基于堆栈的计算机（包括Andrew Tannenbaum教科书中的JVM的硬件实现）根本没有显式寄存器。但是， int 通常与寄存器的大小相同（定义 int 和<$ c的64位环境$ c> long 为32位（向后兼容）是一个例外），指针通常保存一个机器地址，因此通常与寄存器的大小相同（分段存储器模型，例如16位x86，其中地址适合两个寄存器的情况除外），并且 size_t 和 ptrdiff_t 保存数组索引，因此通常是相同的大小作为寄存器（具有64位代码但具有32位存储空间的x32目标是例外）。大多数CPU都有浮点寄存器，每个浮点寄存器都可以容纳 double 来进行数学运算，但有些则不行。

There is no type guaranteed to fit into a register. In fact, some stack-based machines, including the hardware implementation of JVM in Andrew Tannenbaum’s textbook, do not have explicit registers at all. However, an int usually is the same size as a register (64-bit environments that define int and long as 32-bit for backward compatibility are exceptions), a pointer usually holds a machine address and therefore is usually the same size as a register (segmented memory models such as 16-bit x86, where addresses fit into two registers, are exceptions), and size_t and ptrdiff_t hold array indices and are therefore usually the same size as a register (The x32 target, which has 64-bit code but a 32-bit memory space, is an exception). Most CPUs have floating-point registers that can each hold a double to do math on it, but some don’t.

如果您想要的是快速可移植的代码，最好的选择是使用诸如 int_fast16_t 和 uint_fast32_t 来自< stdint.h> 。保证它们是通常最快的尺寸，至少足够宽。在正常的目标上，这将是机器寄存器的大小。

If what you want is fast portable code, your best bet is to use the types such as int_fast16_t and uint_fast32_t from <stdint.h>. These are guaranteed to be the usually-fastest size that’s at least wide enough. and on normal targets, that’s going to be the size of a machine register.

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