cmd/compile: reimplement parameter leak encoding

Currently, escape analysis is able to record at most one dereference
when a parameter leaks to the heap; that is, at call sites, it can't
distinguish between any of these three functions:

    func x1(p ****int) { sink = *p }
    func x2(p ****int) { sink = **p }
    func x3(p ****int) { sink = ***p }

Similarly, it's limited to recording parameter leaks to only the first
4 parameters, and only up to 6 dereferences.

All of these limitations are due to the awkward encoding scheme used
at the moment.

This CL replaces the encoding scheme with a simple [8]uint8 array,
which can handle up to the first 7 parameters, and up to 254
dereferences, which ought to be enough for anyone. And if not, it's
much more easily increased.

Shrinks export data size geometric mean for Kubernetes by 0.07%.

Fixes #33981.

Change-Id: I10a94b9accac9a0c91490e0d6d458316f5ca1e13
Reviewed-on: https://go-review.googlesource.com/c/go/+/197680
Reviewed-by: Cherry Zhang <cherryyz@google.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/test/escape_param.go b/test/escape_param.go
index 5e81de9f46..d8fafc53f8 100644
--- a/test/escape_param.go
+++ b/test/escape_param.go
@@ -205,7 +205,7 @@ func param7(i ***int) { // ERROR "leaking param content: i$"
 
 func caller7() {
 	i := 0      // ERROR "moved to heap: i$"
-	p := &i     // ERROR "moved to heap: p$"
+	p := &i
 	p2 := &p
 	param7(&p2)
 }