Improve unreachability recognition in elog() macro.

Some experimentation with an older version of gcc showed that it is able
to determine whether "if (elevel_ >= ERROR)" is compile-time constant
if elevel_ is declared "const", but otherwise not so much.  We had
accounted for that in ereport() but were too miserly with braces to
make it so in elog().  I don't know how many currently-interesting
compilers have the same quirk, but in case it will save some code
space, let's make sure that elog() is on the same footing as ereport()
for this purpose.

Back-patch to 9.3 where we introduced pg_unreachable() calls into
elog/ereport.

diff --git a/src/include/utils/elog.h b/src/include/utils/elog.h
index 832b984c4c996173016819db3f86ed304a258ccd..4258b650cb663d98572aa1af77289f288821a0eb 100644 (file)
--- a/src/include/utils/elog.h
+++ b/src/include/utils/elog.h
@@ -250,12 +250,13 @@ extern int        getinternalerrposition(void);
 #else                                                  /* !HAVE__BUILTIN_CONSTANT_P */
 #define elog(elevel, ...)  \
        do { \
-               int             elevel_; \
                elog_start(__FILE__, __LINE__, PG_FUNCNAME_MACRO); \
-               elevel_ = (elevel); \
-               elog_finish(elevel_, __VA_ARGS__); \
-               if (elevel_ >= ERROR) \
-                       pg_unreachable(); \
+               { \
+                       const int elevel_ = (elevel); \
+                       elog_finish(elevel_, __VA_ARGS__); \
+                       if (elevel_ >= ERROR) \
+                               pg_unreachable(); \
+               } \
        } while(0)
 #endif   /* HAVE__BUILTIN_CONSTANT_P */
 #else                                                  /* !HAVE__VA_ARGS */