cmd/compile: don't nilcheck newobject and return values from mapaccess{1,2}

They are guaranteed to be non-nil, no point in inserting
nil checks for them.

Fixes #15390

Change-Id: I3b9a0f2319affc2139dcc446d0a56c6785ae5a86
Reviewed-on: https://go-review.googlesource.com/22291
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/test/nilptr3.go b/test/nilptr3.go
index 817d2aec74..1bec833fe3 100644
--- a/test/nilptr3.go
+++ b/test/nilptr3.go
@@ -193,3 +193,24 @@ func f4(x *[10]int) {
 	x = y
 	_ = &x[9] // ERROR "removed repeated nil check"
 }
+
+func m1(m map[int][80]byte) byte {
+	v := m[3] // ERROR "removed nil check"
+	return v[5]
+}
+func m2(m map[int][800]byte) byte {
+	v := m[3] // ERROR "removed nil check"
+	return v[5]
+}
+func m3(m map[int][80]byte) (byte, bool) {
+	v, ok := m[3] // ERROR "removed nil check"
+	return v[5], ok
+}
+func m4(m map[int][800]byte) (byte, bool) {
+	v, ok := m[3] // ERROR "removed nil check"
+	return v[5], ok
+}
+func p1() byte {
+	p := new([100]byte)
+	return p[5] // ERROR "removed nil check"
+}