From: Lynn Boger <laboger@linux.vnet.ibm.com>
Date: Mon, 15 Apr 2024 21:13:57 +0000 (-0500)
Subject: math/big: improve use of addze in mulAddVWW on ppc64x
X-Git-Tag: go1.23rc1~608
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=330bc950933edad89abf6d1eedbfea378cf9fdf6;p=gostls13.git

math/big: improve use of addze in mulAddVWW on ppc64x

Improve the use of addze to avoid unnecessary register
moves on ppc64x.

goos: linux
goarch: ppc64le
pkg: math/big
cpu: POWER10
                 │   old.out    │               new.out               │
                 │    sec/op    │    sec/op     vs base               │
MulAddVWW/1         4.524n ± 3%   4.248n ±  0%   -6.10% (p=0.002 n=6)
MulAddVWW/2         5.634n ± 0%   5.283n ±  0%   -6.24% (p=0.002 n=6)
MulAddVWW/3         6.406n ± 0%   5.918n ±  0%   -7.63% (p=0.002 n=6)
MulAddVWW/4         6.484n ± 0%   5.859n ±  0%   -9.64% (p=0.002 n=6)
MulAddVWW/5         7.363n ± 0%   6.766n ±  0%   -8.11% (p=0.002 n=6)
MulAddVWW/10       10.920n ± 0%   9.856n ±  0%   -9.75% (p=0.002 n=6)
MulAddVWW/100       83.46n ± 0%   66.95n ±  0%  -19.78% (p=0.002 n=6)
MulAddVWW/1000      856.0n ± 0%   681.6n ±  0%  -20.38% (p=0.002 n=6)
MulAddVWW/10000     8.589µ ± 1%   6.774µ ±  0%  -21.14% (p=0.002 n=6)
MulAddVWW/100000    86.22µ ± 0%   67.71µ ± 43%  -21.48% (p=0.065 n=6)
geomean             73.34n        63.62n        -13.26%


Change-Id: I95d6ac49ff6b64aa678e6896f57af9d85c923aad
Reviewed-on: https://go-review.googlesource.com/c/go/+/579235
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Paul Murphy <murp@ibm.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
---

diff --git a/src/math/big/arith_ppc64x.s b/src/math/big/arith_ppc64x.s
index c483e252ab..330bc7e46c 100644
--- a/src/math/big/arith_ppc64x.s
+++ b/src/math/big/arith_ppc64x.s
@@ -514,9 +514,8 @@ TEXT ·mulAddVWW(SB), NOSPLIT, $0
 	MULLD   R9, R20, R6       // R6 = z0 = Low-order(x[i]*y)
 	MULHDU  R9, R20, R7       // R7 = z1 = High-order(x[i]*y)
 	ADDC    R4, R6            // R6 = z0 + r
-	ADDZE   R7                // R7 = z1 + CA
+	ADDZE   R7, R4            // R4 = z1 + CA
 	CMP     R0, R11
-	MOVD    R7, R4            // R4 = c
 	MOVD    R6, 0(R10)        // z[i]
 	BEQ     done
 
@@ -536,20 +535,17 @@ loop:
 	MULLD   R9, R20, R24      // R24 = z0[i]
 	MULHDU  R9, R20, R20      // R20 = z1[i]
 	ADDC    R4, R24           // R24 = z0[i] + c
-	ADDZE   R20               // R7 = z1[i] + CA
 	MULLD   R9, R21, R25
 	MULHDU  R9, R21, R21
-	ADDC    R20, R25
-	ADDZE   R21
+	ADDE    R20, R25
 	MULLD   R9, R22, R26
 	MULHDU  R9, R22, R22
 	MULLD   R9, R23, R27
 	MULHDU  R9, R23, R23
-	ADDC    R21, R26
-	ADDZE   R22
+	ADDE    R21, R26
 	MOVD    R24, 8(R10)       // z[i]
 	MOVD    R25, 16(R10)      // z[i+1]
-	ADDC    R22, R27
+	ADDE    R22, R27
 	ADDZE   R23,R4		  // update carry
 	MOVD    R26, 24(R10)      // z[i+2]
 	MOVDU   R27, 32(R10)      // z[i+3]
@@ -567,10 +563,9 @@ tail:
 	MULHDU  R9, R20, R25      // R25 = z1[i]
 	ADD     $-1, R11          // R11 = z_len - 1
 	ADDC    R4, R24
-	ADDZE   R25
+	ADDZE   R25, R4
 	MOVDU   R24, 8(R10)       // z[i]
 	CMP     R0, R11
-	MOVD    R25, R4           // R4 = c
 	BEQ     done              // If R11 = 0, we are done
 
 	MOVDU   8(R8), R20
@@ -578,10 +573,9 @@ tail:
 	MULHDU  R9, R20, R25
 	ADD     $-1, R11
 	ADDC    R4, R24
-	ADDZE   R25
+	ADDZE   R25, R4
 	MOVDU   R24, 8(R10)
 	CMP     R0, R11
-	MOVD    R25, R4
 	BEQ     done
 
 	MOVD    8(R8), R20
@@ -589,9 +583,8 @@ tail:
 	MULHDU  R9, R20, R25
 	ADD     $-1, R11
 	ADDC    R4, R24
-	ADDZE   R25
+	ADDZE   R25,R4
 	MOVD    R24, 8(R10)
-	MOVD    R25, R4
 
 done:
 	MOVD    R4, c+64(FP)