loop-attribute-conflict
Status: stub. The full-length analysis is queued for a v1.0.x patch release per ADR 0018, section 5, criterion #6. The companion rule page at docs/rules/loop-attribute-conflict.md contains the canonical detection logic + GPU reasoning.
TL;DR
HLSL's loop attributes are mutually exclusive intent declarations, not composable flags. [unroll] tells the compiler to fully replicate the loop body and drop the back-edge entirely; [loop] tells the compiler to keep the loop as a real branch and not unroll. When both attributes appear on the same loop, DXC and Slang both pick one (typically the first declared, but the rule is not part of the spec) and emit a warning that is easy to miss in a noisy build log. The shader still compiles and runs correctly, but the runtime cost depends on which attribute won — and that choice is fragile across compiler versions and back-ends. The same source on the same hardware can swap between unrolled and rolled codegen across a DXC point release, which is exactly the kind of unowned drift this linter exists to catch.
What the rule fires on
A for, while, or do-while loop whose attribute list contains a contradictory pair of compiler hints — most commonly [unroll] together with [loop] on the same statement, or [unroll(N)] with [loop]. The rule also fires on [unroll(N)] where N exceeds a configurable threshold (unroll-max, default 32), because past that bound the unroll either silently degrades to [loop] codegen on every back-end or blows up VGPR pressure to the point of dropping wave occupancy. The rule does not fire on a lone [unroll], a lone [loop], a lone [fastopt], or [unroll(N)] with N at or below the threshold — those are well-formed compiler hints with a single intent.
See the What it detects section of the rule page for the full pattern definition.
Why it matters
The full GPU-mechanism analysis lives in the Why it matters on a GPU section of the companion rule page.
Examples
The bad / good code snippets are kept canonical on the rule page; see loop-attribute-conflict.md -> Examples.
See also
- Rule page -- canonical reference + change log.
- control-flow overview -- broader context.
- ADR 0018 -- v1.0 readiness plan.
This is a v1.0-ship stub. Full analysis pending; track issue link TBD.