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[ Atariscne.org - News ] GCC for asm Experts (and C/C++ Intermediates) - Part 4

Register Allocation and the Cost Model

The m68k has 15 usable registers: d0-d7 and a0-a6 (a7 is the stack pointer, and sometimes a6 is also reserved as a frame pointer). For a CPU from 1979, this is actually quite generous; the 6502 has three, the Z80 and 8086 have seven or eight. So 15 should be plenty, right?

Not so fast. We have two register files with different capabilities. A pointer must be in an address register to dereference it. Most arithmetic must happen in data registers. For many use cases, we effectively have 7 or 8 registers to choose from, not 15. And if our function calls others, the ABI reserves the caller-clobbered registers, effectively leaving only ten registers: d3-d7/a2-a6 for free use with fastcall. When we run out, the allocator spills to the stack: on 68000, each 16-bit spill costs at least 16 cycles (8 to read, 8 to write back), and 32-bit values adds another 8. In a tight loop, it adds up fast.

When you write assembly, register allocation is intuition. You look at a routine and think: I need this value for the next three instructions, then I can reuse the register for something else. You juggle lifetimes in your head, naturally overlapping short-lived values. Teaching a computer this intuition is the fundamental challenge. The answer is to build a graph of which pseudo-registers are live simultaneously; two pseudos that overlap in lifetime interfere and cannot share a register. Then color the graph with K colors, one per available register, starting with the cheap caller-clobbered regs. When 19 pseudos from put_pixel compete for 15 registers, some will not fit — especially once you account for the data/address split — and those get spilled.

So how does GCC make the best of a difficult situation? 

[ Atariscne.org - News ] Revision 2026 shapshots

Here are a few snapshots from Revision, provided by Lotek Style and Samurai. thanks for sending those in!

Atarisceners spotted (from top left to down right): Havoc, Samurai, Havoc again (there can never be enough Havoc), NebulaH, Gunstick, Sgt Slayer (Atrocity!), JAC!, Lotek Style - not on the photo: Spiny and Havoc's friend with the sun glasses from last year ;p

A group photo may follow.

[ Atariscne.org - News ] Outline 2026 webpage online

The Outline Party 2026 will take place from May 14th to 17th! The freshly baked website is now available, so better get out your remote controls!

🔗 Outline 2026 website

[ Atariscne.org - News ] Adventures in Retro - A new diskmag for the ‘other’ 16 bitter!

Why is Atariscne.org reporting on a release of a new Amiga diskmag eh, CiH?

Well, yours truly offered to help out a friend, a little side-project, as it were.

‘Adventures in Retro’ is a long term project, created by a very good friend known as ‘Woodycool’ or Duncan, in civilian life. He’s a UK based retro-fan, primarily Amiga, but he also takes in a wide range of 8-bit interests, such as Commodore C16/Plus 4 and Amstrad CPC. He also owns and enjoys an Atari ST or two, so he’s living up to the ‘cool’ part of his nom-de-scene. 

Anyway, I’ve been tempted to add a few articles, the sort of thing that wouldn’t fit easily in to atariscene.org. There is the future possibility that this mag could be released in other formats, including Atari.

If you have one of the other 16 bit machines, here’s a link to the home page, with a download of the first issue. -  https://www.adv-in-retro.uk/ - It’s pretty compatible with most Amiga’s.

I do have an Amiga 600 waiting to be resurrected and slightly upgraded. I’ve been using the OSZX Online Amiga emulator in the meantime - OSZX Online Emulator

Anyway, enjoy!

CiH - Atariscne.org - April 2026.

[ Demozoo ] The Meteoriks 2026 - Congratulations, Laureates!

The Meteoriks Award 2026 for NEW TALENT goes to DJ_Level_3 & Marv1994 for Primer
https://demozoo.org/productions/371249

The Meteoriks Award 2026 for OUTSTANDING CONCEPT goes to ReelTime by Demostue Allst★rs
https://demozoo.org/productions/379064
with an Honorable Mention of No-CPU Challenge by Demostue Allst★rs
https://demozoo.org/productions/376675

The Meteoriks Award 2026 for BEST EXECUTABLE GRAPHICS goes to Heritages by iapafoto
https://demozoo.org/productions/371224

The Meteoriks Award 2026 for [b]BEST OLDSCHOOL PRODUCTION goes to
Codeboys & Endians by Booze Design
https://demozoo.org/productions/366745

The Meteoriks Award 2026 for BEST MIDSCHOOL PRODUCTION goes to
Vaporous by The Twitch Elite
https://demozoo.org/productions/371134

The Meteoriks Award 2026 for BEST SOUNDTRACK goes to AddMortem by Arise & Joker
https://demozoo.org/productions/370512

The Meteoriks Award 2026 for OUTSTANDING TECHNICAL ACHIEVEMENT goes to
Small64 by N64Brew
https://demozoo.org/productions/371258
with an Honorable Mention of The 2025 Rotozoomer Challenge by Batman Group, Capsule, DESiRE, DHS, Django, Lemon, Loonies, Tarnow & mis, TTE
https://demozoo.org/search/?q=%5Brotozoomer-challenge%5D+year%3A2025

The Meteoriks Award 2026 for BEST VISUALS goes to
Brute Concrete by Digital Dynamite & United Force
https://demozoo.org/productions/377656

The Meteoriks Award 2026 for BEST TINY INTRO
goes to
Party.DLL by Desire & Haujobb
https://demozoo.org/productions/371106
with an Honorable Mention of Starpath by HellMood / Desire
https://demozoo.org/productions/367702

The Meteoriks Award 2026 for BEST HIGH-END INTRO goes to
Tension by Digital Dynamite & Aenima
https://demozoo.org/productions/371364

The Meteoriks Award 2026 for BEST DIRECTION goes to
Hexer by LJ
https://demozoo.org/productions/371094

The Meteoriks Award 2026 for BEST HIGH-END DEMO goes to
BREACH by mfx
https://demozoo.org/productions/371397