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, 6 insertions, 12 deletions

diff --git a/src/backend/utils/adt/oracle_compat.c b/src/backend/utils/adt/oracle_compat.c
index b82016500b0..a5aa6a95aa7 100644
--- a/src/backend/utils/adt/oracle_compat.c
+++ b/src/backend/utils/adt/oracle_compat.c
@@ -15,6 +15,7 @@
  */
 #include "postgres.h"
 
+#include "common/int.h"
 #include "utils/builtins.h"
 #include "utils/formatting.h"
 #include "mb/pg_wchar.h"
@@ -1045,19 +1046,12 @@ repeat(PG_FUNCTION_ARGS)
 		count = 0;
 
 	slen = VARSIZE_ANY_EXHDR(string);
-	tlen = VARHDRSZ + (count * slen);
 
-	/* Check for integer overflow */
-	if (slen != 0 && count != 0)
-	{
-		int			check = count * slen;
-		int			check2 = check + VARHDRSZ;
-
-		if ((check / slen) != count || check2 <= check)
-			ereport(ERROR,
-					(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
-					 errmsg("requested length too large")));
-	}
+	if (unlikely(pg_mul_s32_overflow(count, slen, &tlen)) ||
+		unlikely(pg_add_s32_overflow(tlen, VARHDRSZ, &tlen)))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+				 errmsg("requested length too large")));
 
 	result = (text *) palloc(tlen);