From 395d6b5005b8e3854aa628ad98757dc053a8549c Mon Sep 17 00:00:00 2001
From: chenyifan <chenyifan62@huawei.com>
Date: Tue, 18 Nov 2025 19:35:07 +0800
Subject: [PATCH] Add goexperiment.StepOpt2 for optimized step function in
 runtime

---
 src/internal/goexperiment/exp_stepopt2_off.go |  8 ++++
 src/internal/goexperiment/exp_stepopt2_on.go  |  8 ++++
 src/internal/goexperiment/flags.go            |  3 ++
 src/runtime/symtab.go                         | 47 +++++++++++++++++++
 4 files changed, 66 insertions(+)
 create mode 100644 src/internal/goexperiment/exp_stepopt2_off.go
 create mode 100644 src/internal/goexperiment/exp_stepopt2_on.go

diff --git a/src/internal/goexperiment/exp_stepopt2_off.go b/src/internal/goexperiment/exp_stepopt2_off.go
new file mode 100644
index 000000000..7a06da83f
--- /dev/null
+++ b/src/internal/goexperiment/exp_stepopt2_off.go
@@ -0,0 +1,8 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.stepopt2
+
+package goexperiment
+
+const StepOpt2 = false
+const StepOpt2Int = 0
diff --git a/src/internal/goexperiment/exp_stepopt2_on.go b/src/internal/goexperiment/exp_stepopt2_on.go
new file mode 100644
index 000000000..1cd2d7d60
--- /dev/null
+++ b/src/internal/goexperiment/exp_stepopt2_on.go
@@ -0,0 +1,8 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.stepopt2
+
+package goexperiment
+
+const StepOpt2 = true
+const StepOpt2Int = 1
diff --git a/src/internal/goexperiment/flags.go b/src/internal/goexperiment/flags.go
index 87ddd355f..f39a282fe 100644
--- a/src/internal/goexperiment/flags.go
+++ b/src/internal/goexperiment/flags.go
@@ -115,4 +115,7 @@ type Flags struct {
 
 	//PageNum enables 128k span size
 	PageNum bool
+
+	// StepOpt2 enables optimization for func step in package runtime
+	StepOpt2 bool
 }
diff --git a/src/runtime/symtab.go b/src/runtime/symtab.go
index b47f2d839..ef2163447 100644
--- a/src/runtime/symtab.go
+++ b/src/runtime/symtab.go
@@ -7,6 +7,7 @@ package runtime
 import (
 	"internal/abi"
 	"internal/goarch"
+	"internal/goexperiment"
 	"runtime/internal/atomic"
 	"runtime/internal/sys"
 	"unsafe"
@@ -1069,6 +1070,9 @@ func funcdata(f funcInfo, i uint8) unsafe.Pointer {
 
 // step advances to the next pc, value pair in the encoded table.
 func step(p []byte, pc *uintptr, val *int32, first bool) (newp []byte, ok bool) {
+	if goexperiment.StepOpt2 {
+		return step_exp2(p, pc, val, first)
+	}
 	// For both uvdelta and pcdelta, the common case (~70%)
 	// is that they are a single byte. If so, avoid calling readvarint.
 	uvdelta := uint32(p[0])
@@ -1092,6 +1096,49 @@ func step(p []byte, pc *uintptr, val *int32, first bool) (newp []byte, ok bool)
 	return p, true
 }
 
+func step_exp2(p []byte, pc *uintptr, val *int32, first bool) (newp []byte, ok bool) {
+	// For both uvdelta and pcdelta, the common case (~70%)
+	// is that they are a single byte. If so, avoid calling readvarint.
+	var n uint32
+	uvdelta := uint32(p[0])
+	if uvdelta == 0 && !first {
+		return nil, false
+	}
+	if uvdelta&0x80 == 0 {
+		n = 1
+		*val += int32(-(uvdelta & 1) ^ (uvdelta >> 1))
+		p = p[n:]
+	} else {
+		a := uint32(p[1])
+		if a&0x80 == 0 {
+			uvdelta = (uvdelta & 0x7f) | (a << 7)
+			n = 2
+		} else {
+			n, uvdelta = readvarint(p)
+		}
+		*val += int32(-(uvdelta & 1) ^ (uvdelta >> 1))
+		p = p[n:]
+	}
+
+	pcdelta := uint32(p[0]) // load 2-byte once
+	if pcdelta&0x80 == 0 {
+		n = 1
+		*pc += uintptr((pcdelta & 0xff) * sys.PCQuantum)
+		p = p[n:]
+	} else {
+		a := uint32(p[1])
+		if a&0x80 == 0 {
+			pcdelta = (pcdelta & 0x7f) | (a << 7)
+			n = 2
+		} else {
+			n, pcdelta = readvarint(p)
+		}
+		p = p[n:]
+		*pc += uintptr(pcdelta * sys.PCQuantum)
+	}
+	return p, true
+}
+
 // readvarint reads a varint from p.
 func readvarint(p []byte) (read uint32, val uint32) {
 	var v, shift, n uint32
-- 
Gitee