[perf] ShapeText heap-allocates the cache-key std::string on every call, including hits (UI-Shared.cpp) #122

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opened 2026-06-17 21:18:54 +02:00 by jorijnvdgraaf · 0 comments

jorijnvdgraaf commented

2026-06-17 21:18:54 +02:00

Owner

Found by an adversarially-verified performance audit (confirmed real after a skeptic pass).

Location: implementations/Crafter.Graphics-UI-Shared.cpp:78-79
Severity: medium · Effort: moderate · Category: allocation

Problem

ShapeText builds ShapedRunKey{..., std::string(utf8)} before find() unconditionally, including on cache hits, on the per-frame onBuild path. N labels = N string copies + hashes (+ frees for non-SSO strings) per frame, partially defeating the run cache.

Fix

is_transparent transparent hash + equality on shapedRuns_; probe with a view-key {const Font*, float, array<float,4>, string_view} and materialize the owning std::string only on miss for emplace.

Found by an adversarially-verified performance audit (confirmed real after a skeptic pass). **Location:** `implementations/Crafter.Graphics-UI-Shared.cpp:78-79` **Severity:** medium · **Effort:** moderate · **Category:** allocation ### Problem `ShapeText` builds `ShapedRunKey{..., std::string(utf8)}` before `find()` unconditionally, including on cache hits, on the per-frame `onBuild` path. N labels = N string copies + hashes (+ frees for non-SSO strings) per frame, partially defeating the run cache. ### Fix `is_transparent` transparent hash + equality on `shapedRuns_`; probe with a view-key `{const Font*, float, array<float,4>, string_view}` and materialize the owning `std::string` only on miss for `emplace`.

jorijnvdgraaf added the

claude:ready

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2026-06-17 21:34:39 +02:00