From 5a5e31c38b97dc76e3683727ff8106e79da73c76 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Fri, 2 Feb 2024 05:58:54 +0530
Subject: [PATCH] Also zero upper at start of function

---
 tools/simdstring/generate.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/simdstring/generate.go b/tools/simdstring/generate.go
index 07e4f96b7..fdbd2bf80 100644
--- a/tools/simdstring/generate.go
+++ b/tools/simdstring/generate.go
@@ -1048,6 +1048,10 @@ func (s *Function) OutputASM(w io.Writer) {
 	s.print_signature(w)
 	fmt.Fprintf(w, "\nTEXT ·%s(SB), NOSPLIT, $0-%d\n", s.Name, s.Size)
 
+	if s.Used256BitReg {
+		fmt.Fprintln(w, "\tVZEROUPPER // zero upper bits of AVX registers to avoid dependencies when switching between SSE and AVX code")
+	}
+
 	s.Return()
 	for _, i := range s.Instructions {
 		fmt.Fprintln(w, i)