0001-Apply-auto-vectorization-to-the-inner-loop-of-div_va.patch

From 41732ad9a44dcd12e52d823fb59cb23cce4fe217 Mon Sep 17 00:00:00 2001
From: Dean Rasheed <dean.a.rasheed@gmail.com>
Date: Sun, 20 Feb 2022 12:45:01 +0000
Subject: [PATCH 1/3] Apply auto-vectorization to the inner loop of
 div_var_fast().

This loop is basically the same as the inner loop of mul_var(), which
was auto-vectorized in commit 8870917623, but the compiler will only
consider auto-vectorizing the div_var_fast() loop if the assignment
target div[qi + i] is replaced by div_qi[i], where div_qi = &div[qi].

Additionally, since the compiler doesn't know that qdigit is
guaranteed to fit in a 16-bit NumericDigit, cast it to NumericDigit
before multiplying to make the resulting auto-vectorized code more
efficient.
---
 src/backend/utils/adt/numeric.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c
index 3208789f75..fc43d2a456 100644
--- a/src/backend/utils/adt/numeric.c
+++ b/src/backend/utils/adt/numeric.c
@@ -8908,13 +8908,22 @@ div_var_fast(const NumericVar *var1, const NumericVar *var2,
 			 * which would make the new value simply div[qi] mod vardigits[0].
 			 * The lower-order terms in qdigit can change this result by not
 			 * more than about twice INT_MAX/NBASE, so overflow is impossible.
+			 *
+			 * This inner loop is the performance bottleneck for division, so
+			 * code it in the same way as the inner loop of mul_var() so that
+			 * it can be auto-vectorized.  We cast qdigit to NumericDigit
+			 * before multiplying to allow the compiler to generate more
+			 * efficient code (using 16-bit multiplication), which is safe
+			 * since we know that the quotient digit is off by at most one, so
+			 * there is no overflow risk.
 			 */
 			if (qdigit != 0)
 			{
 				int			istop = Min(var2ndigits, div_ndigits - qi + 1);
+				int		   *div_qi = &div[qi];
 
 				for (i = 0; i < istop; i++)
-					div[qi + i] -= qdigit * var2digits[i];
+					div_qi[i] -= ((NumericDigit) qdigit) * var2digits[i];
 			}
 		}
 
-- 
2.26.2