[Peter Eisentraut <peter.eisentraut@2ndquadrant.com>]

On 2/21/17 22:17, Andres Freund wrote:
> I've not run comparisons this year, but late last year I was seeing > 5%
> < 10% benefits - that seems plenty enough to care.

You mean the 5-minute benchmarks on my laptop are not representative? ;-)

Here is a patch that I had lying around that clears the compiler
warnings under -O3 for me.  It seems that they are a subset of what you
are seeing.  Plausibly, as compilers are doing more analysis in larger
scopes, we can expect to see more of these.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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Attachments:

0001-Silence-compiler-warnings-from-gcc-O3.patch (text/x-patch, 2.8K) download
From 2a73d3ac095435ecbe3aefff7bcecc292675e167 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter_e@gmx.net>
Date: Wed, 22 Feb 2017 09:23:40 -0500
Subject: [PATCH] Silence compiler warnings from gcc -O3

---
 src/backend/commands/dbcommands.c | 13 +++++++------
 src/backend/utils/adt/varlena.c   |  6 ++++++
 src/backend/utils/misc/guc.c      |  2 +-
 3 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 1ebacbc24f..2a23f634c5 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -27,6 +27,7 @@
 #include "access/genam.h"
 #include "access/heapam.h"
 #include "access/htup_details.h"
+#include "access/multixact.h"
 #include "access/xact.h"
 #include "access/xloginsert.h"
 #include "access/xlogutils.h"
@@ -103,14 +104,14 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	Relation	rel;
 	Oid			src_dboid;
 	Oid			src_owner;
-	int			src_encoding;
-	char	   *src_collate;
-	char	   *src_ctype;
+	int			src_encoding = -1;
+	char	   *src_collate = NULL;
+	char	   *src_ctype = NULL;
 	bool		src_istemplate;
 	bool		src_allowconn;
-	Oid			src_lastsysoid;
-	TransactionId src_frozenxid;
-	MultiXactId src_minmxid;
+	Oid			src_lastsysoid = InvalidOid;
+	TransactionId src_frozenxid = InvalidTransactionId;
+	MultiXactId src_minmxid = InvalidMultiXactId;
 	Oid			src_deftablespace;
 	volatile Oid dst_deftablespace;
 	Relation	pg_database_rel;
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index 28b5745ba8..7da7535b3b 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -1129,6 +1129,8 @@ text_position_setup(text *t1, text *t2, TextPositionState *state)
 		state->use_wchar = false;
 		state->str1 = VARDATA_ANY(t1);
 		state->str2 = VARDATA_ANY(t2);
+		state->wstr1 = 0;
+		state->wstr2 = 0;
 		state->len1 = len1;
 		state->len2 = len2;
 	}
@@ -1144,6 +1146,8 @@ text_position_setup(text *t1, text *t2, TextPositionState *state)
 		len2 = pg_mb2wchar_with_len(VARDATA_ANY(t2), p2, len2);
 
 		state->use_wchar = true;
+		state->str1 = 0;
+		state->str2 = 0;
 		state->wstr1 = p1;
 		state->wstr2 = p2;
 		state->len1 = len1;
@@ -1227,6 +1231,8 @@ text_position_setup(text *t1, text *t2, TextPositionState *state)
 				state->skiptable[wstr2[i] & skiptablemask] = last - i;
 		}
 	}
+	else
+		state->skiptablemask = 255;
 }
 
 static int
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 24771389c8..107e1f2957 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -9275,7 +9275,7 @@ RestoreGUCState(void *gucstate)
 	char	   *varname,
 			   *varvalue,
 			   *varsourcefile;
-	int			varsourceline;
+	int			varsourceline = -1;
 	GucSource	varsource;
 	GucContext	varscontext;
 	char	   *srcptr = (char *) gucstate;
-- 
2.11.1