From da89464a63a7c181e928a68f4ac392bd841a00b2 Mon Sep 17 00:00:00 2001
From: Ayke van Laethem <aykevanlaethem@gmail.com>
Date: Sat, 20 Oct 2018 17:22:51 +0200
Subject: [PATCH] compiler: compare slice against nil

---
 compiler/compiler.go | 13 +++++++++++++
 testdata/slice.go    |  2 ++
 testdata/slice.txt   |  2 ++
 3 files changed, 17 insertions(+)

diff --git a/compiler/compiler.go b/compiler/compiler.go
index f6063a0d..4d833061 100644
--- a/compiler/compiler.go
+++ b/compiler/compiler.go
@@ -2863,6 +2863,19 @@ func (c *Compiler) parseBinOp(frame *Frame, binop *ssa.BinOp) (llvm.Value, error
 		default:
 			return llvm.Value{}, errors.New("todo: binop on pointer: " + binop.Op.String())
 		}
+	case *types.Slice:
+		// Slices are in general not comparable, but can be compared against
+		// nil. Assume at least one of them is nil to make the code easier.
+		xPtr := c.builder.CreateExtractValue(x, 0, "")
+		yPtr := c.builder.CreateExtractValue(y, 0, "")
+		switch binop.Op {
+		case token.EQL: // ==
+			return c.builder.CreateICmp(llvm.IntEQ, xPtr, yPtr, ""), nil
+		case token.NEQ: // !=
+			return c.builder.CreateICmp(llvm.IntNE, xPtr, yPtr, ""), nil
+		default:
+			return llvm.Value{}, errors.New("todo: binop on slice: " + binop.Op.String())
+		}
 	default:
 		return llvm.Value{}, errors.New("unknown binop type: " + binop.X.Type().String())
 	}
diff --git a/testdata/slice.go b/testdata/slice.go
index c5e4a330..8fcbffff 100644
--- a/testdata/slice.go
+++ b/testdata/slice.go
@@ -4,6 +4,7 @@ func main() {
 	l := 5
 	foo := []int{1, 2, 4, 5}
 	bar := make([]int, l-2, l)
+	println("foo is nil?", foo == nil, nil == foo)
 	printslice("foo", foo)
 	printslice("bar", bar)
 	printslice("foo[1:2]", foo[1:2])
@@ -15,6 +16,7 @@ func main() {
 
 	// append
 	var grow []int
+	println("slice is nil?", grow == nil, nil == grow)
 	printslice("grow", grow)
 	grow = append(grow, 42)
 	printslice("grow", grow)
diff --git a/testdata/slice.txt b/testdata/slice.txt
index 81973655..75a32d10 100644
--- a/testdata/slice.txt
+++ b/testdata/slice.txt
@@ -1,9 +1,11 @@
+foo is nil? false false
 foo: len=4 cap=4 data: 1 2 4 5
 bar: len=3 cap=5 data: 0 0 0
 foo[1:2]: len=1 cap=3 data: 2
 sum foo: 12
 copy foo -> bar: 3
 bar: len=3 cap=5 data: 1 2 4
+slice is nil? true true
 grow: len=0 cap=0 data:
 grow: len=1 cap=1 data: 42
 grow: len=3 cap=4 data: 42 -1 -2