On Wed, 2023-06-28 at 18:22 +0800, WANG Xuerui wrote: > > is "ori t0, zero, CSR_PRMD_PIE" hard to understand? It is basic > > arithmetic instr and easy to understand also. To be frank I do not > > see the advantage of using li.w, also there is no document that > > pseudo-instruction should be used with high priority. > It depends on the reader. Sure the semantics are the same, but with "ori > xx, zero, xx" someone's always going to wonder "why do 'x = 0 | > something' when you can simply li.w", because even if it's easy to > understand it's still an extra level of indirection. > > And I've given the historical and general software engineering > perspective too; it's not something set in stone, but I'd expect general > software development best practices and minimizing any *possible* reader > confusion to be acceptable. The pseudo *should* be the high priority in general. If we don't consider the pseudos high priority, people will start to load immediates with "their own way", like writing "addi.w $t0, $zero, 42" or even "xori $t0, $zero, 42" for "42". These may puzzle the uarch, causing a performance worse than "ori $t0, $zero, 42". So the only rationale things are either: 1. Telling people always use pseudos if possible. or 2. Telling people "remember to use ori for loading small immediates, not other instructions". 1 is obviously easier. -- Xi Ruoyao <xry111@xxxxxxxxxxx> School of Aerospace Science and Technology, Xidian University
