From 6d7dc5350042697bbb141a7362649db7fa67bd55 Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Wed, 14 Feb 2018 14:17:28 -0800
Subject: [PATCH] Return implementation defined value if pg_$op_s$bit_overflow
 overflows.

Some older compilers otherwise sometimes complain about undefined
values, even though the return value should not be used in the
overflow case.  We assume that any decent compiler will optimize away
the unnecessary assignment in performance critical cases.

We do not want to restrain the returned value to a specific value,
e.g. 0 or the wrapped-around value, because some fast ways to
implement overflow detecting math do not easily allow for
that (e.g. msvc intrinsics).  As the function documentation already
documents the returned value in case of intrinsics to be
implementation defined, no documentation has to be updated.

Per complaint from Tom Lane and his buildfarm member prairiedog.

Author: Andres Freund
Discussion: https://postgr.es/m/18169.1513958454@sss.pgh.pa.us
---
 src/include/common/int.h | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/src/include/common/int.h b/src/include/common/int.h
index feb84102b4..82e38d4b7b 100644
--- a/src/include/common/int.h
+++ b/src/include/common/int.h
@@ -34,7 +34,10 @@ pg_add_s16_overflow(int16 a, int16 b, int16 *result)
 	int32		res = (int32) a + (int32) b;
 
 	if (res > PG_INT16_MAX || res < PG_INT16_MIN)
+	{
+		*result = 0x5EED; /* to avoid spurious warnings */
 		return true;
+	}
 	*result = (int16) res;
 	return false;
 #endif
@@ -54,7 +57,10 @@ pg_sub_s16_overflow(int16 a, int16 b, int16 *result)
 	int32		res = (int32) a - (int32) b;
 
 	if (res > PG_INT16_MAX || res < PG_INT16_MIN)
+	{
+		*result = 0x5EED; /* to avoid spurious warnings */
 		return true;
+	}
 	*result = (int16) res;
 	return false;
 #endif
@@ -74,7 +80,10 @@ pg_mul_s16_overflow(int16 a, int16 b, int16 *result)
 	int32		res = (int32) a * (int32) b;
 
 	if (res > PG_INT16_MAX || res < PG_INT16_MIN)
+	{
+		*result = 0x5EED; /* to avoid spurious warnings */
 		return true;
+	}
 	*result = (int16) res;
 	return false;
 #endif
@@ -94,7 +103,10 @@ pg_add_s32_overflow(int32 a, int32 b, int32 *result)
 	int64		res = (int64) a + (int64) b;
 
 	if (res > PG_INT32_MAX || res < PG_INT32_MIN)
+	{
+		*result = 0x5EED; /* to avoid spurious warnings */
 		return true;
+	}
 	*result = (int32) res;
 	return false;
 #endif
@@ -114,7 +126,10 @@ pg_sub_s32_overflow(int32 a, int32 b, int32 *result)
 	int64		res = (int64) a - (int64) b;
 
 	if (res > PG_INT32_MAX || res < PG_INT32_MIN)
+	{
+		*result = 0x5EED; /* to avoid spurious warnings */
 		return true;
+	}
 	*result = (int32) res;
 	return false;
 #endif
@@ -134,7 +149,10 @@ pg_mul_s32_overflow(int32 a, int32 b, int32 *result)
 	int64		res = (int64) a * (int64) b;
 
 	if (res > PG_INT32_MAX || res < PG_INT32_MIN)
+	{
+		*result = 0x5EED; /* to avoid spurious warnings */
 		return true;
+	}
 	*result = (int32) res;
 	return false;
 #endif
@@ -154,13 +172,19 @@ pg_add_s64_overflow(int64 a, int64 b, int64 *result)
 	int128		res = (int128) a + (int128) b;
 
 	if (res > PG_INT64_MAX || res < PG_INT64_MIN)
+	{
+		*result = 0x5EED; /* to avoid spurious warnings */
 		return true;
+	}
 	*result = (int64) res;
 	return false;
 #else
 	if ((a > 0 && b > 0 && a > PG_INT64_MAX - b) ||
 		(a < 0 && b < 0 && a < PG_INT64_MIN - b))
+	{
+		*result = 0x5EED; /* to avoid spurious warnings */
 		return true;
+	}
 	*result = a + b;
 	return false;
 #endif
@@ -180,13 +204,19 @@ pg_sub_s64_overflow(int64 a, int64 b, int64 *result)
 	int128		res = (int128) a - (int128) b;
 
 	if (res > PG_INT64_MAX || res < PG_INT64_MIN)
+	{
+		*result = 0x5EED; /* to avoid spurious warnings */
 		return true;
+	}
 	*result = (int64) res;
 	return false;
 #else
 	if ((a < 0 && b > 0 && a < PG_INT64_MIN + b) ||
 		(a > 0 && b < 0 && a > PG_INT64_MAX + b))
+	{
+		*result = 0x5EED; /* to avoid spurious warnings */
 		return true;
+	}
 	*result = a - b;
 	return false;
 #endif
@@ -206,7 +236,10 @@ pg_mul_s64_overflow(int64 a, int64 b, int64 *result)
 	int128		res = (int128) a * (int128) b;
 
 	if (res > PG_INT64_MAX || res < PG_INT64_MIN)
+	{
+		*result = 0x5EED; /* to avoid spurious warnings */
 		return true;
+	}
 	*result = (int64) res;
 	return false;
 #else
@@ -229,6 +262,7 @@ pg_mul_s64_overflow(int64 a, int64 b, int64 *result)
 		 (a < 0 && b > 0 && a < PG_INT64_MIN / b) ||
 		 (a < 0 && b < 0 && a < PG_INT64_MAX / b)))
 	{
+		*result = 0x5EED; /* to avoid spurious warnings */
 		return true;
 	}
 	*result = a * b;
-- 
2.40.0