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, 33 insertions, 0 deletions

diff --git a/test/nilptr5.go b/test/nilptr5.go
new file mode 100644
index 0000000000..2c48c0b261
--- /dev/null
+++ b/test/nilptr5.go
@@ -0,0 +1,33 @@
+// errorcheck -0 -d=nil
+
+// +build !wasm
+// +build !aix
+
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Test that nil checks are removed.
+// Optimization is enabled.
+
+package p
+
+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"
+}
+
+// make sure to remove nil check for memory move (issue #18003)
+func f8(t *[8]int) [8]int {
+	return *t // ERROR "removed nil check"
+}