cmd/compile: teach prove about len's & cap's max based on the element size

Change-Id: I88056fada1ff488c199fce54cf737dbdd091214d
Reviewed-on: https://go-review.googlesource.com/c/go/+/695095
Auto-Submit: Jorropo <jorropo.pgm@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/test/prove.go b/test/prove.go
index ef7690bbde..70a27865cf 100644
--- a/test/prove.go
+++ b/test/prove.go
@@ -2330,6 +2330,18 @@ func issue74473(s []uint) {
 	}
 }
 
+func setCapMaxBasedOnElementSize(x []uint64) int {
+	c := uintptr(cap(x))
+	max := ^uintptr(0) >> 3
+	if c > max { // ERROR "Disproved Less"
+		return 42
+	}
+	if c <= max { // ERROR "Proved Leq"
+		return 1337
+	}
+	return 0
+}
+
 //go:noinline
 func useInt(a int) {
 }