cmd/compile: allow conversion from slice to array ptr

Panic if the slice is too short. Updates #395 Change-Id: I90f4bff2da5d8f3148ba06d2482084f32b25c29a Reviewed-on: https://go-review.googlesource.com/c/go/+/301650 Trust: Josh Bleecher Snyder <josharian@gmail.com> Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com> Reviewed-by: Matthew Dempsky <mdempsky@google.com>
golang · Apr 21, 2021 · faa4fa1 · faa4fa1
1 parent 1c26843
commit faa4fa1
Show file tree

Hide file tree

Showing 33 changed files with 380 additions and 141 deletions.
diff --git a/src/cmd/compile/internal/escape/escape.go b/src/cmd/compile/internal/escape/escape.go
@@ -669,7 +669,10 @@ func (e *escape) exprSkipInit(k hole, n ir.Node) {
 			k = e.spill(k, n)
 		}
 		e.expr(k.note(n, "interface-converted"), n.X)
-
+	case ir.OSLICE2ARRPTR:
+		// the slice pointer flows directly to the result
+		n := n.(*ir.ConvExpr)
+		e.expr(k, n.X)
 	case ir.ORECV:
 		n := n.(*ir.UnaryExpr)
 		e.discard(n.X)

diff --git a/src/cmd/compile/internal/ir/expr.go b/src/cmd/compile/internal/ir/expr.go
@@ -277,7 +277,7 @@ func (n *ConvExpr) SetOp(op Op) {
 	switch op {
 	default:
 		panic(n.no("SetOp " + op.String()))
-	case OCONV, OCONVIFACE, OCONVNOP, OBYTES2STR, OBYTES2STRTMP, ORUNES2STR, OSTR2BYTES, OSTR2BYTESTMP, OSTR2RUNES, ORUNESTR:
+	case OCONV, OCONVIFACE, OCONVNOP, OBYTES2STR, OBYTES2STRTMP, ORUNES2STR, OSTR2BYTES, OSTR2BYTESTMP, OSTR2RUNES, ORUNESTR, OSLICE2ARRPTR:
 		n.op = op
 	}
 }

diff --git a/src/cmd/compile/internal/ir/fmt.go b/src/cmd/compile/internal/ir/fmt.go
@@ -206,6 +206,7 @@ var OpPrec = []int{
 	OPRINT:         8,
 	ORUNESTR:       8,
 	OSIZEOF:        8,
+	OSLICE2ARRPTR:  8,
 	OSTR2BYTES:     8,
 	OSTR2RUNES:     8,
 	OSTRUCTLIT:     8,
@@ -804,7 +805,8 @@ func exprFmt(n Node, s fmt.State, prec int) {
 		ORUNES2STR,
 		OSTR2BYTES,
 		OSTR2RUNES,
-		ORUNESTR:
+		ORUNESTR,
+		OSLICE2ARRPTR:
 		n := n.(*ConvExpr)
 		if n.Type() == nil || n.Type().Sym() == nil {
 			fmt.Fprintf(s, "(%v)", n.Type())

diff --git a/src/cmd/compile/internal/ir/node.go b/src/cmd/compile/internal/ir/node.go
@@ -137,6 +137,7 @@ const (
 	OSTR2BYTES    // Type(Left) (Type is []byte, Left is a string)
 	OSTR2BYTESTMP // Type(Left) (Type is []byte, Left is a string, ephemeral)
 	OSTR2RUNES    // Type(Left) (Type is []rune, Left is a string)
+	OSLICE2ARRPTR // Type(Left) (Type is *[N]T, Left is a []T)
 	// Left = Right or (if Colas=true) Left := Right
 	// If Colas, then Ninit includes a DCL node for Left.
 	OAS

diff --git a/src/cmd/compile/internal/ir/op_string.go b/src/cmd/compile/internal/ir/op_string.go
diff --git a/src/cmd/compile/internal/ssa/expand_calls.go b/src/cmd/compile/internal/ssa/expand_calls.go
@@ -508,7 +508,7 @@ func (x *expandState) rewriteSelect(leaf *Value, selector *Value, offset int64,
 		ls := x.rewriteSelect(leaf, selector.Args[0], offset, regOffset)
 		locs = x.splitSlots(ls, ".ptr", 0, x.typs.BytePtr)
 
-	case OpSlicePtr:
+	case OpSlicePtr, OpSlicePtrUnchecked:
 		w := selector.Args[0]
 		ls := x.rewriteSelect(leaf, w, offset, regOffset)
 		locs = x.splitSlots(ls, ".ptr", 0, types.NewPtr(w.Type.Elem()))
@@ -1202,7 +1202,7 @@ func expandCalls(f *Func) {
 			case OpStructSelect, OpArraySelect,
 				OpIData, OpITab,
 				OpStringPtr, OpStringLen,
-				OpSlicePtr, OpSliceLen, OpSliceCap,
+				OpSlicePtr, OpSliceLen, OpSliceCap, OpSlicePtrUnchecked,
 				OpComplexReal, OpComplexImag,
 				OpInt64Hi, OpInt64Lo:
 				w := v.Args[0]

diff --git a/src/cmd/compile/internal/ssa/gen/dec.rules b/src/cmd/compile/internal/ssa/gen/dec.rules
@@ -56,6 +56,7 @@
 (SlicePtr (SliceMake ptr _ _ )) => ptr
 (SliceLen (SliceMake _ len _)) => len
 (SliceCap (SliceMake _ _ cap)) => cap
+(SlicePtrUnchecked (SliceMake ptr _ _ )) => ptr
 
 (Load <t> ptr mem) && t.IsSlice() =>
   (SliceMake

diff --git a/src/cmd/compile/internal/ssa/gen/genericOps.go b/src/cmd/compile/internal/ssa/gen/genericOps.go
@@ -479,6 +479,10 @@ var genericOps = []opData{
 	{name: "SlicePtr", argLength: 1, typ: "BytePtr"}, // ptr(arg0)
 	{name: "SliceLen", argLength: 1},                 // len(arg0)
 	{name: "SliceCap", argLength: 1},                 // cap(arg0)
+	// SlicePtrUnchecked, like SlicePtr, extracts the pointer from a slice.
+	// SlicePtr values are assumed non-nil, because they are guarded by bounds checks.
+	// SlicePtrUnchecked values can be nil.
+	{name: "SlicePtrUnchecked", argLength: 1},
 
 	// Complex (part/whole)
 	{name: "ComplexMake", argLength: 2}, // arg0=real, arg1=imag

diff --git a/src/cmd/compile/internal/ssa/op.go b/src/cmd/compile/internal/ssa/op.go
@@ -469,6 +469,7 @@ const (
 	BoundsSlice3BU                      // ... with unsigned high
 	BoundsSlice3C                       // 3-arg slicing operation, 0 <= low <= high failed
 	BoundsSlice3CU                      // ... with unsigned low
+	BoundsConvert                       // conversion to array pointer failed
 	BoundsKindCount
 )
 
@@ -496,7 +497,8 @@ func boundsABI(b int64) int {
 	case BoundsSlice3Alen,
 		BoundsSlice3AlenU,
 		BoundsSlice3Acap,
-		BoundsSlice3AcapU:
+		BoundsSlice3AcapU,
+		BoundsConvert:
 		return 0
 	case BoundsSliceAlen,
 		BoundsSliceAlenU,