dead-store-sv-target
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/dead-store-sv-target.md contains the canonical detection logic + GPU reasoning.
TL;DR
A dead store to an SV_Target output variable computes and writes a value that the GPU will never read. The computation of the dead value — any arithmetic, texture samples, or other operations that produced it — is wasted ALU and memory bandwidth. On AMD RDNA and NVIDIA Turing, the compiler may eliminate simple constant dead stores (e.g., result = float4(1,0,0,1) followed by an unconditional override), but it cannot in general eliminate dead stores whose right-hand side involves function calls, texture samples, or control-flow-dependent values without a full inter-procedural dead-code elimination pass — which GPU shader compilers rarely perform at the full-program scale.
What the rule fires on
An assignment to a pixel-shader output variable carrying the SV_Target semantic (or to a local variable that is returned as SV_Target) where that assignment is immediately overwritten on all paths before the value is returned or used. The first write is a dead store: it is never read, so the computation and the write are wasted. The rule uses Slang's reflection API to identify SV_Target-typed outputs and a light data-flow pass to detect write-before-read patterns within the same function scope. See tests/fixtures/phase3/bindings_extra.hlsl, lines 42–46 for the ps_dead_store example: float4 result = float4(1,0,0,1) is written and then immediately overwritten by result = float4(0,1,0,1) before result is used.
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 dead-store-sv-target.md -> Examples.
See also
- Rule page -- canonical reference + change log.
- bindings overview -- broader context.
- ADR 0018 -- v1.0 readiness plan.
This is a v1.0-ship stub. Full analysis pending; track issue link TBD.