Kaboom: do not build it on a GCC that cannot instantiate it - #10
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Kaboom's port count is large enough that going through the boost.pfr aggregate fallback exhausts the compiler. g++-14 peaks at 40.9 GB and is OOM-killed; -fsyntax-only alone reaches 10 GB, so the cost is front-end instantiation and no optimisation flag reduces it (-O0, -O1, -fno-inline-functions, -finline-limit and the ggc params all behave identically). GCC only leaves that fallback with P1061 packs, i.e. g++ >= 16 built as C++26, where the same TU compiles in 151 s at 7.1 GB. Skip the object everywhere else rather than letting the build die. clang is unaffected: it has taken the structured path since 21. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Ux7eanJYt46tkpQhitnk2r
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Compiling
Kaboom/Kaboom.hppwith GCC runs the compiler out of memory.It is the front end, not codegen
-fsyntax-onlyperforms no code generation at all, and still dies:-O3(40 GB cap)-O1(30 GB cap)-O0-O2-fno-inline-functions-finline-limit=100/=40--param inline-unit-growth=5 --param large-function-growth=20-O2 --param ggc-min-expand=10 --param ggc-min-heapsize=32768-fsyntax-onlyMemory grows ~9.4 GB/min, linearly. Since every optimisation level and every inliner knob behaves identically, and
-fsyntax-onlyreproduces it, this is template instantiation — nothing in the optimiser is involved and no flag can help.Cause and the one configuration that works
GCC < 16 has no P1061 structured-binding packs, so avendish selects the
boost.pfraggregate backend, and instantiating pfr over Kaboom's ~336-field aggregate is what exhausts the front end. Getting off pfr fixes it:gnu++23gnu++23gnu++23gnu++26So the guard tests the version and the standard: g++-16 in C++23 mode still selects pfr and still dies, so the version alone would not be a safe test.
clang is unaffected — it has been on the structured backend since 21, and the wasm lane (clang 23) selects it already at
gnu++23.Guard truth table, verified by evaluating the expression in CMake:
Companion fix in avendish, where g++-15 currently selects a backend it cannot compile: celtera/avendish#190