cmd/compile: fix nilcheck for AIX

This commit adapts compile tool to create correct nilchecks for AIX.

AIX allows to load a nil pointer. Therefore, the default nilcheck
which issues a load must be replaced by a CMP instruction followed by a
store at 0x0 if the value is nil. The store will trigger a SIGSEGV as on
others OS.

The nilcheck algorithm must be adapted to do not remove nilcheck if it's
only a read. Stores are detected with v.Type.IsMemory().

Tests related to nilptr must be adapted to the previous changements.
nilptr.go cannot be used as it's because the AIX address space starts at
1<<32.

Change-Id: I9f5aaf0b7e185d736a9b119c0ed2fe4e5bd1e7af
Reviewed-on: https://go-review.googlesource.com/c/144538
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 1 insertions, 20 deletions

diff --git a/test/nilptr3.go b/test/nilptr3.go
index 6aa718e027..e0f2ed9767 100644
--- a/test/nilptr3.go
+++ b/test/nilptr3.go
@@ -1,6 +1,7 @@
 // errorcheck -0 -d=nil
 
 // +build !wasm
+// +build !aix
 
 // Copyright 2013 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -192,21 +193,6 @@ func f4(x *[10]int) {
 	_ = &x[9] // ERROR "removed[a-z ]* nil check"
 }
 
-func f5(p *float32, q *float64, r *float32, s *float64) float64 {
-	x := float64(*p) // ERROR "removed nil check"
-	y := *q          // ERROR "removed nil check"
-	*r = 7           // ERROR "removed nil check"
-	*s = 9           // ERROR "removed nil check"
-	return x + y
-}
-
-type T [29]byte
-
-func f6(p, q *T) {
-	x := *p // ERROR "removed nil check"
-	*q = x  // ERROR "removed nil check"
-}
-
 func m1(m map[int][80]byte) byte {
 	v := m[3] // ERROR "removed nil check"
 	return v[5]
@@ -257,11 +243,6 @@ func f7() (*Struct, float64) {
 	return t, *p // ERROR "removed nil check"
 }
 
-// make sure to remove nil check for memory move (issue #18003)
-func f8(t *[8]int) [8]int {
-	return *t // ERROR "removed nil check"
-}
-
 func f9() []int {
 	x := new([1]int)
 	x[0] = 1  // ERROR "removed nil check"