<br><br><div class="gmail_quote">On Tue, Mar 17, 2009 at 2:45 PM, Claus Kick <span dir="ltr"><<a href="mailto:claus_kick@web.de">claus_kick@web.de</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Eliot Miranda wrote:<br>
*snip*<div class="im"><br>
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...and SPARC is one of the worst 64-bit implementations out there.<br>
Question, how much bigger is a 64-bit literal load instruction vs a 32-bit<br>
literal load in x86/x86-64 and SPARC32/SPARC64?<br>
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Interesting though off topic tidbit, therefore an OT question: is that aimed at SPARC as a (for lack of better word) architecture or do you have a specific implementation in mind? (*curious*)</blockquote><div><br></div><div>
I know nothing about SPARC internals and so cannot suggest an implementation.</div><div><br></div><div>Part of my complaint is the name, Scaleable Processor ARCitecture. The current SPARC requires 6 (reads it and weep, _6_) 32-bit instructions to synthesize an arbitrary 64-bit literal. It hasn't scaled to 64-bits; consequently there are a range of addressing models in 64-bit SPARC compilers, 20-something-bits 40-something bits (I forget the details) and 64-bits. By contrast there are 10-byte instructions that do 64-bit literals loads in x86-64. So a 200% overhead vs a 25% overhead.</div>
<div><br></div><div>One can try and use the branch and link instruction to jump over the literal, grab the pc and indirect through it, but IIRC that's a slow 5 word sequence that can't be used in leaf routines. But this is off the top of my head so don't quote me.</div>
<div><br></div><div>I would have thought that somehow one could define a three word instruction saying "load the next two words into a register and skip them: or, if the anachronism of the delay slot must still be respected, a 4 word instruction saying "load the two words after the following instruction into a register and skip them, executing the instruction in the delay slot".</div>
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