From: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Date: Tue, 2 Nov 2021 03:19:24 +0000 (+0700)
Subject: cmd/compile: explain special treatment when rewrite slice literal args
X-Git-Tag: go1.18beta1~616
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=58fb05a24a756a9a4386faff977e6495cdccb12f;p=gostls13.git

cmd/compile: explain special treatment when rewrite slice literal args

Followup discussion in CL 360055.

Change-Id: I36212c2a497b152d01ed86d244d5f57bd34a64a6
Reviewed-on: https://go-review.googlesource.com/c/go/+/360614
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
---

diff --git a/src/cmd/compile/internal/escape/call.go b/src/cmd/compile/internal/escape/call.go
index 63e790a786..d1215afca8 100644
--- a/src/cmd/compile/internal/escape/call.go
+++ b/src/cmd/compile/internal/escape/call.go
@@ -333,7 +333,24 @@ func (e *escape) rewriteArgument(argp *ir.Node, init *ir.Nodes, call ir.Node, fn
 		}
 	}
 
-	// Peel away any slice lits.
+	// Peel away any slice literals for better escape analyze
+	// them. For example:
+	//
+	//     go F([]int{a, b})
+	//
+	// If F doesn't escape its arguments, then the slice can
+	// be allocated on the new goroutine's stack.
+	//
+	// For variadic functions, the compiler has already rewritten:
+	//
+	//     f(a, b, c)
+	//
+	// to:
+	//
+	//     f([]T{a, b, c}...)
+	//
+	// So we need to look into slice elements to handle uintptr(ptr)
+	// arguments to syscall-like functions correctly.
 	if arg := *argp; arg.Op() == ir.OSLICELIT {
 		list := arg.(*ir.CompLitExpr).List
 		for i := range list {