register-allocation - w3toppers.com

Why do compilers insist on using a callee-saved register here?

TL:DR: Compiler internals are probably not set up to look for this optimization easily, and it’s probably only useful around small functions, not inside large functions between calls. Inlining to create large functions is a better solution most of the time There can be a latency vs. throughput tradeoff if foo happens not to save/restore … Read more

Address of register variable

Here’s an excerpt from Section 6.7.1 (footnote 101) of the C99 standard (pdf): The implementation may treat any register declaration simply as an auto declaration. However, whether or not addressable storage is actually used, the address of any part of an object declared with storage-class specifier register cannot be computed, either explicitly (by use of … Read more