[dev.ssa] cmd/compile: implement OSLICESTR

Add a new function and generic operation to handle
bounds checking for slices. Unlike the index
bounds checking the index can be equal to the upper
bound.

Do gc-friendly slicing that generates proper code for
0-length result slices.

This is a takeover of Alexandru's original change,
(https://go-review.googlesource.com/#/c/12764/)
submittable now that the decompose phase is in.

Change-Id: I17d164cf42ed7839f84ca949c6ad3289269c9160
Reviewed-on: https://go-review.googlesource.com/13903
Reviewed-by: David Chase <drchase@google.com>

1 files changed, 92 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/gc/testdata/string_ssa.go b/src/cmd/compile/internal/gc/testdata/string_ssa.go
new file mode 100644
index 0000000000..5987412933
--- /dev/null
+++ b/src/cmd/compile/internal/gc/testdata/string_ssa.go
@@ -0,0 +1,92 @@
+// string_ssa.go tests string operations.
+package main
+
+var failed = false
+
+func testStringSlice1_ssa(a string, i, j int) string {
+	switch { // prevent inlining
+	}
+	return a[i:]
+}
+
+func testStringSlice2_ssa(a string, i, j int) string {
+	switch { // prevent inlining
+	}
+	return a[:j]
+}
+
+func testStringSlice12_ssa(a string, i, j int) string {
+	switch { // prevent inlining
+	}
+	return a[i:j]
+}
+
+func testStringSlice() {
+	tests := [...]struct {
+		fn        func(string, int, int) string
+		s         string
+		low, high int
+		want      string
+	}{
+		// -1 means the value is not used.
+		{testStringSlice1_ssa, "foobar", 0, -1, "foobar"},
+		{testStringSlice1_ssa, "foobar", 3, -1, "bar"},
+		{testStringSlice1_ssa, "foobar", 6, -1, ""},
+		{testStringSlice2_ssa, "foobar", -1, 0, ""},
+		{testStringSlice2_ssa, "foobar", -1, 3, "foo"},
+		{testStringSlice2_ssa, "foobar", -1, 6, "foobar"},
+		{testStringSlice12_ssa, "foobar", 0, 6, "foobar"},
+		{testStringSlice12_ssa, "foobar", 0, 0, ""},
+		{testStringSlice12_ssa, "foobar", 6, 6, ""},
+		{testStringSlice12_ssa, "foobar", 1, 5, "ooba"},
+		{testStringSlice12_ssa, "foobar", 3, 3, ""},
+		{testStringSlice12_ssa, "", 0, 0, ""},
+	}
+
+	for i, t := range tests {
+		if got := t.fn(t.s, t.low, t.high); t.want != got {
+			println("#", i, " ", t.s, "[", t.low, ":", t.high, "] = ", got, " want ", t.want)
+			failed = true
+		}
+	}
+}
+
+type prefix struct {
+	prefix string
+}
+
+func (p *prefix) slice_ssa() {
+	p.prefix = p.prefix[:3]
+}
+
+func testStructSlice() {
+	switch {
+	}
+	p := &prefix{"prefix"}
+	p.slice_ssa()
+	if "pre" != p.prefix {
+		println("wrong field slice: wanted %s got %s", "pre", p.prefix)
+	}
+}
+
+func testStringSlicePanic() {
+	defer func() {
+		if r := recover(); r != nil {
+			println("paniced as expected")
+		}
+	}()
+
+	str := "foobar"
+	println("got ", testStringSlice12_ssa(str, 3, 9))
+	println("expected to panic, but didn't")
+	failed = true
+}
+
+func main() {
+	testStringSlice()
+	testStringSlicePanic()
+
+	if failed {
+		panic("failed")
+	}
+}