cmd/compile/internal/gc: handle arith ops in samesafeexpr

Teach samesafeexpr to handle arithmetic unary and binary ops.

It makes map lookup optimization possible in

	m[k+1] = append(m[k+1], ...)
	m[-k] = append(m[-k], ...)
	... etc

Does not cover "+" for strings (concatenation).

Change-Id: Ibbb16ac3faf176958da344be1471b06d7cf33a6c
Reviewed-on: https://go-review.googlesource.com/135795
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/gc/typecheck.go

@@ -3298,7 +3298,8 @@ func samesafeexpr(l *Node, r *Node) bool {
 	case ODOT, ODOTPTR:
 		return l.Sym != nil && r.Sym != nil && l.Sym == r.Sym && samesafeexpr(l.Left, r.Left)
 
-	case OIND, OCONVNOP:
+	case OIND, OCONVNOP,
+		ONOT, OCOM, OPLUS, OMINUS:
 		return samesafeexpr(l.Left, r.Left)
 
 	case OCONV:
@@ -3306,7 +3307,8 @@ func samesafeexpr(l *Node, r *Node) bool {
 		// Allow only numeric-ish types. This is a bit conservative.
 		return issimple[l.Type.Etype] && samesafeexpr(l.Left, r.Left)
 
-	case OINDEX, OINDEXMAP:
+	case OINDEX, OINDEXMAP,
+		OADD, OSUB, OOR, OXOR, OMUL, OLSH, ORSH, OAND, OANDNOT, ODIV, OMOD:
 		return samesafeexpr(l.Left, r.Left) && samesafeexpr(l.Right, r.Right)
 
 	case OLITERAL:

test/codegen/mapaccess.go

@@ -304,6 +304,18 @@ func mapAppendAssignmentInt32() {
 	// arm64:-".*mapaccess"
 	m[k] = append(m[k], a...)
 
+	// 386:-".*mapaccess"
+	// amd64:-".*mapaccess"
+	// arm:-".*mapaccess"
+	// arm64:-".*mapaccess"
+	m[k+1] = append(m[k+1], a...)
+
+	// 386:-".*mapaccess"
+	// amd64:-".*mapaccess"
+	// arm:-".*mapaccess"
+	// arm64:-".*mapaccess"
+	m[-k] = append(m[-k], a...)
+
 	// Exceptions
 
 	// 386:".*mapaccess"
@@ -349,6 +361,18 @@ func mapAppendAssignmentInt64() {
 	// arm64:-".*mapaccess"
 	m[k] = append(m[k], a...)
 
+	// 386:-".*mapaccess"
+	// amd64:-".*mapaccess"
+	// arm:-".*mapaccess"
+	// arm64:-".*mapaccess"
+	m[k+1] = append(m[k+1], a...)
+
+	// 386:-".*mapaccess"
+	// amd64:-".*mapaccess"
+	// arm:-".*mapaccess"
+	// arm64:-".*mapaccess"
+	m[-k] = append(m[-k], a...)
+
 	// Exceptions
 
 	// 386:".*mapaccess"