From bf9d8b4ad9f579cd1beb740289a1f4b6545d0c84 Mon Sep 17 00:00:00 2001
From: shupiaoyang <shupiaoyang1@huawei.com>
Date: Tue, 2 Dec 2025 10:45:46 +0800
Subject: [PATCH] Add goexperiment.StepOpt2 and optimize runtime step function

---
 src/internal/goexperiment/exp_stepopt_off.go |  8 ++++
 src/internal/goexperiment/exp_stepopt_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_stepopt_off.go
 create mode 100644 src/internal/goexperiment/exp_stepopt_on.go

diff --git a/src/internal/goexperiment/exp_stepopt_off.go b/src/internal/goexperiment/exp_stepopt_off.go
new file mode 100644
index 000000000..bca12c06e
--- /dev/null
+++ b/src/internal/goexperiment/exp_stepopt_off.go
@@ -0,0 +1,8 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.stepopt
+
+package goexperiment
+
+const StepOpt = false
+const StepOptInt = 0
diff --git a/src/internal/goexperiment/exp_stepopt_on.go b/src/internal/goexperiment/exp_stepopt_on.go
new file mode 100644
index 000000000..957d2daac
--- /dev/null
+++ b/src/internal/goexperiment/exp_stepopt_on.go
@@ -0,0 +1,8 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.stepopt
+
+package goexperiment
+
+const StepOpt = true
+const StepOptInt = 1
diff --git a/src/internal/goexperiment/flags.go b/src/internal/goexperiment/flags.go
index ac85fc800..4b3b0f8ab 100644
--- a/src/internal/goexperiment/flags.go
+++ b/src/internal/goexperiment/flags.go
@@ -131,4 +131,7 @@ type Flags struct {
 
 	// Kunpeng malloc prefetch optimization.
 	PrefetchMalloc bool
+
+	// StepOpt enables optimization for func step in package runtime
+	StepOpt bool
 }
diff --git a/src/runtime/symtab.go b/src/runtime/symtab.go
index 8c6ef2b4f..608ec524a 100644
--- a/src/runtime/symtab.go
+++ b/src/runtime/symtab.go
@@ -7,6 +7,7 @@ package runtime
 import (
 	"internal/abi"
 	"internal/goarch"
+	"internal/goexperiment"
 	"internal/runtime/atomic"
 	"internal/runtime/sys"
 	"unsafe"
@@ -1246,6 +1247,9 @@ 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.StepOpt {
+		return stepOpt(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])
@@ -1269,6 +1273,49 @@ func step(p []byte, pc *uintptr, val *int32, first bool) (newp []byte, ok bool)
 	return p, true
 }
 
+func stepOpt(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
-- 
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