cmd/compile: use len(s)<=cap(s) to remove more bounds checks

When we discover a relation x <= len(s), also discover the relation
x <= cap(s).  That way, in situations like:

a := s[x:]  // tests 0 <= x <= len(s)
b := s[:x]  // tests 0 <= x <= cap(s)

the second check can be eliminated.

Fixes #16813

Change-Id: Ifc037920b6955e43bac1a1eaf6bac63a89cfbd44
Reviewed-on: https://go-review.googlesource.com/33633
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alexandru Moșoi <alexandru@mosoi.ro>
Reviewed-by: David Chase <drchase@google.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/test/checkbce.go b/test/checkbce.go
index 59bd41b360..4f9574d420 100644
--- a/test/checkbce.go
+++ b/test/checkbce.go
@@ -50,7 +50,7 @@ func f5(a []int) {
 	if len(a) > 5 {
 		useInt(a[5])
 		useSlice(a[6:])
-		useSlice(a[:6]) // ERROR "Found IsSliceInBounds$"
+		useSlice(a[:6])
 	}
 }