From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 10 Sep 2016 21:54:23 +0000 (-0400)
Subject: Improve unreachability recognition in elog() macro.
X-Git-Tag: REL9_6_0~32
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=fa7b3a88dd5d7f6d18614eefc6cc0662e31bd451;p=postgresql

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 f4ff03ec8a..70dc365465 100644
--- a/src/include/utils/elog.h
+++ b/src/include/utils/elog.h
@@ -206,12 +206,13 @@ 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 */