Use new overflow aware integer operations.

A previous commit added inline functions that provide fast(er) and
correct overflow checks for signed integer math. Use them in a
significant portion of backend code.  There's more to touch in both
backend and frontend code, but these were the easily identifiable
cases.

The old overflow checks are noticeable in integer heavy workloads.

A secondary benefit is that getting rid of overflow checks that rely
on signed integer overflow wrapping around, will allow us to get rid
of -fwrapv in the future. Which in turn slows down other code.

Author: Andres Freund
Discussion: https://postgr.es/m/20171024103954.ztmatprlglz3rwke@alap3.anarazel.de

1 files changed, 23 insertions, 18 deletions

diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c
index 82e6f4483bd..e9a6ca3535d 100644
--- a/src/backend/utils/adt/numeric.c
+++ b/src/backend/utils/adt/numeric.c
@@ -28,6 +28,7 @@
 
 #include "access/hash.h"
 #include "catalog/pg_type.h"
+#include "common/int.h"
 #include "funcapi.h"
 #include "lib/hyperloglog.h"
 #include "libpq/pqformat.h"
@@ -6169,8 +6170,7 @@ numericvar_to_int64(const NumericVar *var, int64 *result)
 	int			ndigits;
 	int			weight;
 	int			i;
-	int64		val,
-				oldval;
+	int64		val;
 	bool		neg;
 	NumericVar	rounded;
 
@@ -6196,27 +6196,25 @@ numericvar_to_int64(const NumericVar *var, int64 *result)
 	weight = rounded.weight;
 	Assert(weight >= 0 && ndigits <= weight + 1);
 
-	/* Construct the result */
+	/*
+	 * Construct the result. To avoid issues with converting a value
+	 * corresponding to INT64_MIN (which can't be represented as a positive 64
+	 * bit two's complement integer), accumulate value as a negative number.
+	 */
 	digits = rounded.digits;
 	neg = (rounded.sign == NUMERIC_NEG);
-	val = digits[0];
+	val = -digits[0];
 	for (i = 1; i <= weight; i++)
 	{
-		oldval = val;
-		val *= NBASE;
-		if (i < ndigits)
-			val += digits[i];
+		if (unlikely(pg_mul_s64_overflow(val, NBASE, &val)))
+		{
+			free_var(&rounded);
+			return false;
+		}
 
-		/*
-		 * The overflow check is a bit tricky because we want to accept
-		 * INT64_MIN, which will overflow the positive accumulator.  We can
-		 * detect this case easily though because INT64_MIN is the only
-		 * nonzero value for which -val == val (on a two's complement machine,
-		 * anyway).
-		 */
-		if ((val / NBASE) != oldval)	/* possible overflow? */
+		if (i < ndigits)
 		{
-			if (!neg || (-val) != val || val == 0 || oldval < 0)
+			if (unlikely(pg_sub_s64_overflow(val, digits[i], &val)))
 			{
 				free_var(&rounded);
 				return false;
@@ -6226,7 +6224,14 @@ numericvar_to_int64(const NumericVar *var, int64 *result)
 
 	free_var(&rounded);
 
-	*result = neg ? -val : val;
+	if (!neg)
+	{
+		if (unlikely(val == INT64_MIN))
+			return false;
+		val = -val;
+	}
+	*result = val;
+
 	return true;
 }