Gcc

This one walks you through GCC flag selection for different build modes: debug with `-g -Og`, release with `-O2` or `-O3 -march=native`, size-optimized with `-Os`, and sanitizer builds. It covers LTO and PGO workflows step by step, warning flag discipline with `-Wall -Wextra`, and a triage table for common errors like undefined references and ABI mismatches. The optimization decision tree is practical, especially the note that `-O3` can regress performance due to instruction cache pressure. If you've ever second-guessed whether to enable `-flto` or wondered why `-Ofast` broke your floating point math, this gives you the exact invocations and explains the tradeoffs without the usual compiler flag folklore.