fix(cmake): don't pass -fno-fat-lto-objects on Apple GCC - #6114
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GCC on macOS has no linker plugin, so `-fno-fat-lto-objects` makes every LTO probe fail and LTO is silently disabled. Plain `-flto=auto` works. Fixes pybind#6060 Assisted-by: ClaudeCode:claude-opus-5 Claude-Session: https://claude.ai/code/session_013JABmnjt9oAh29p1pytAB3
henryiii
marked this pull request as ready for review
July 26, 2026 03:03
rwgk
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Jul 27, 2026
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See #6112.
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Description
GCC on macOS has no linker plugin.
-fno-fat-lto-objectsneeds one, socc1plusfails with "-fno-fat-lto-objectsare supported only with linker plugin". Because the LTO probe always adds this flag for non-MinGW GNU compilers, every probe (-flto=auto,-flto) fails and LTO is silently disabled, although plain-flto=autoworks.This change skips the flag when
APPLEis set.Verified with Homebrew
g++-16on macOS: before,HAS_FLTO_AUTOandHAS_FLTOboth fail andpybind11::ltois disabled; after,HAS_FLTO_AUTOsucceeds andpybind11::ltois enabled. The Apple Clang path is unchanged.Fixes #6060
Suggested changelog entry:
-fno-fat-lto-objectsto GCC on macOS, which made all LTO probes fail and silently disabled LTO.https://claude.ai/code/session_013JABmnjt9oAh29p1pytAB3