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Improve handling of ereport(ERROR) and elog(ERROR).
In commit 71450d7, we added code to inform suitably-intelligent compilers that ereport() doesn't return if the elevel is ERROR or higher. This patch extends that to elog(), and also fixes a double-evaluation hazard that the previous commit created in ereport(), as well as reducing the emitted code size. The elog() improvement requires the compiler to support __VA_ARGS__, which should be available in just about anything nowadays since it's required by C99. But our minimum language baseline is still C89, so add a configure test for that. The previous commit assumed that ereport's elevel could be evaluated twice, which isn't terribly safe --- there are already counterexamples in xlog.c. On compilers that have __builtin_constant_p, we can use that to protect the second test, since there's no possible optimization gain if the compiler doesn't know the value of elevel. Otherwise, use a local variable inside the macros to prevent double evaluation. The local-variable solution is inferior because (a) it leads to useless code being emitted when elevel isn't constant, and (b) it increases the optimization level needed for the compiler to recognize that subsequent code is unreachable. But it seems better than not teaching non-gcc compilers about unreachability at all. Lastly, if the compiler has __builtin_unreachable(), we can use that instead of abort(), resulting in a noticeable code savings since no function call is actually emitted. However, it seems wise to do this only in non-assert builds. In an assert build, continue to use abort(), so that the behavior will be predictable and debuggable if the "impossible" happens. These changes involve making the ereport and elog macros emit do-while statement blocks not just expressions, which forces small changes in a few call sites. Andres Freund, Tom Lane, Heikki Linnakangas
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Showing with 361 additions and 15 deletions.
- +58 −1 config/c-compiler.m4
- +178 −0 configure
- +3 −0 configure.in
- +7 −1 contrib/cube/cubescan.l
- +7 −1 contrib/seg/segscan.l
- +7 −1 src/backend/bootstrap/bootscanner.l
- +7 −1 src/backend/parser/scan.l
- +7 −1 src/backend/replication/repl_scanner.l
- +12 −0 src/include/c.h
- +9 −0 src/include/pg_config.h.in
- +9 −0 src/include/pg_config.h.win32
- +57 −9 src/include/utils/elog.h
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