In sha1, the arguments to Write escape if block is in assembler, even if we mark the
assembler routine with go:noescape, but they should not.

% r
go build -gcflags=-m 
# crypto/sha1
./sha1.go:57: can inline (*digest).Size
./sha1.go:59: can inline (*digest).BlockSize
./sha1.go:40: (*digest).Reset d does not escape
./sha1.go:52: new(digest) escapes to heap
./sha1.go:57: (*digest).Size d does not escape
./sha1.go:59: (*digest).BlockSize d does not escape
./sha1.go:61: leaking param: d
./sha1.go:74: d.x escapes to heap
./sha1.go:61: leaking param: d
./sha1.go:61: (*digest).Write p does not escape
./sha1.go:85: (*digest).Write d.x does not escape
./sha1.go:92: moved to heap: d
./sha1.go:99: d escapes to heap
./sha1.go:101: d escapes to heap
./sha1.go:109: d escapes to heap
./sha1.go:90: leaking param: in to result ~anon1
./sha1.go:90: (*digest).Sum d0 does not escape
./sha1.go:99: (*digest).Sum tmp does not escape
./sha1.go:101: (*digest).Sum tmp does not escape
./sha1.go:109: (*digest).Sum tmp does not escape
./sha1.go:123: (*digest).Sum digest does not escape
./sha1block_decl.go:11: block dig does not escape
./sha1block_decl.go:11: block p does not escape
tubenose=% hg diff .
diff -r f6de76ff41a3 src/pkg/crypto/sha1/sha1block_decl.go
--- a/src/pkg/crypto/sha1/sha1block_decl.go Mon Jun 24 16:53:13 2013 -0700
+++ b/src/pkg/crypto/sha1/sha1block_decl.go Mon Jun 24 17:18:52 2013 -0700
@@ -6,4 +6,6 @@
 
 package sha1
 
+//go:noescape
+
 func block(dig *digest, p []byte)
% 
% 


Now a magic trick: Compile the block declaration first.

tubenose=% mv sha1block_decl.go A.go   ###### NOTE: put sha1block_decl.go first in
compilation
tubenose=% go build -gcflags=-m 
# crypto/sha1
./sha1.go:57: can inline (*digest).Size
./sha1.go:59: can inline (*digest).BlockSize
./A.go:11: block dig does not escape
./A.go:11: block p does not escape
./sha1.go:40: (*digest).Reset d does not escape
./sha1.go:52: new(digest) escapes to heap
./sha1.go:57: (*digest).Size d does not escape
./sha1.go:59: (*digest).BlockSize d does not escape
./sha1.go:61: (*digest).Write d does not escape
./sha1.go:61: (*digest).Write p does not escape
./sha1.go:74: (*digest).Write d.x does not escape
./sha1.go:85: (*digest).Write d.x does not escape
./sha1.go:90: leaking param: in to result ~anon1
./sha1.go:90: (*digest).Sum d0 does not escape
./sha1.go:99: (*digest).Sum d does not escape
./sha1.go:99: (*digest).Sum tmp does not escape
./sha1.go:101: (*digest).Sum d does not escape
./sha1.go:101: (*digest).Sum tmp does not escape
./sha1.go:109: (*digest).Sum d does not escape
./sha1.go:109: (*digest).Sum tmp does not escape
./sha1.go:123: (*digest).Sum digest does not escape

Now the arguments to Write do not escape.