register存储类被显式弃用移除的原因探究（数值计算视角）

Great question—especially since register was once a handy optimization hint for numerical computing, where squeezing every bit of performance out of frequent variable access mattered a lot. Let’s dig into why it got explicitly removed:

• Modern compilers render manual hints obsolete
  Back in the day, compilers were far less sophisticated. Programmers needed to tell the compiler which variables (like loop counters or frequently updated numerical values) should live in CPU registers instead of RAM. But today’s optimizing compilers do this automatically—and far better than humans. They analyze variable usage patterns, lifetimes, and hot paths across the entire program to allocate registers optimally, avoiding conflicts and maximizing cache efficiency that a manual register keyword could never match.

• The register keyword had annoying, unnecessary restrictions
  If you marked a variable as register, you couldn’t take its address with &. This became a frustrating constraint as programs grew more complex, even in numerical computing. Worse, compilers often ignored the register hint anyway—they’d put variables in registers when it made sense, regardless of the keyword, and ignore it when the variable needed to be addressable. So the keyword was more of a confusing suggestion than a meaningful directive.

• C standards prioritize simplicity and removing redundancy
  The C standard committee has long focused on trimming features that no longer serve a purpose or are replaced by better mechanisms. register fell into this category: its original purpose (hinting at register allocation) is now handled automatically, and its restrictions just added unnecessary complexity to the language. Removing it cleans up the standard and avoids confusing new programmers who might waste time trying to use a keyword that does nothing useful.

For numerical computing specifically, this isn’t a loss—compilers now do a better job of optimizing register usage than any manual register annotation ever could. You’ll get faster code by writing clear, maintainable numerical code and letting the compiler do its job, rather than relying on outdated hints.

内容的提问来源于stack exchange，提问作者K.R.Park