compiler: make sure make([]T, ...) checks for Ts bigger than 1

Without this, the following code would not panic:

    func getInt(i int) { return i }
    make([][1<<18], getInt(1<<18))

Or this code would be allowed to compile for 32-bit systems:

    make([][1<<18], 1<<18)

compiler/compiler.go

@@ -1481,9 +1481,16 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 		}
 		var buf llvm.Value
 		if expr.Heap {
+			size := c.targetData.TypeAllocSize(typ)
+			// Calculate ^uintptr(0)
+			maxSize := llvm.ConstNot(llvm.ConstInt(c.uintptrType, 0, false)).ZExtValue()
+			if size > maxSize {
+				// Size would be truncated if truncated to uintptr.
+				return llvm.Value{}, c.makeError(expr.Pos(), fmt.Sprintf("value is too big (%v bytes)", size))
+			}
 			// TODO: escape analysis
-			size := llvm.ConstInt(c.uintptrType, c.targetData.TypeAllocSize(typ), false)
+			sizeValue := llvm.ConstInt(c.uintptrType, size, false)
-			buf = c.createRuntimeCall("alloc", []llvm.Value{size}, expr.Comment)
+			buf = c.createRuntimeCall("alloc", []llvm.Value{sizeValue}, expr.Comment)
 			buf = c.builder.CreateBitCast(buf, llvm.PointerType(typ, 0), "")
 		} else {
 			buf = c.builder.CreateAlloca(typ, expr.Comment)
@@ -1727,6 +1734,15 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 			return llvm.Value{}, nil
 		}
 		elemSize := c.targetData.TypeAllocSize(llvmElemType)
+		elemSizeValue := llvm.ConstInt(c.uintptrType, elemSize, false)
+
+		// Calculate ^uintptr(0)
+		maxSize := llvm.ConstNot(llvm.ConstInt(c.uintptrType, 0, false)).ZExtValue()
+		if elemSize > maxSize {
+			// This seems to be checked by the typechecker already, but let's
+			// check it again just to be sure.
+			return llvm.Value{}, c.makeError(expr.Pos(), fmt.Sprintf("slice element type is too big (%v bytes)", elemSize))
+		}
 
 		// Bounds checking.
 		if !frame.fn.IsNoBounds() {
@@ -1754,12 +1770,14 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 					sliceCap = c.builder.CreateSExt(sliceCap, biggestInt, "")
 				}
 			}
-			c.createRuntimeCall(checkFunc, []llvm.Value{sliceLen, sliceCap}, "")
+			// Note: the max element size needs to be doubled to make sure it
+			// fits in an int for, for example, len().
+			elemSizeDoubled := c.builder.CreateMul(elemSizeValue, llvm.ConstInt(c.uintptrType, 2, false), "")
+			c.createRuntimeCall(checkFunc, []llvm.Value{sliceLen, sliceCap, elemSizeDoubled}, "")
 		}
 
 		// Allocate the backing array.
 		// TODO: escape analysis
-		elemSizeValue := llvm.ConstInt(c.uintptrType, elemSize, false)
 		sliceCapCast, err := c.parseConvert(expr.Cap.Type(), types.Typ[types.Uintptr], sliceCap, expr.Pos())
 		if err != nil {
 			return llvm.Value{}, err

src/runtime/panic.go

@@ -57,15 +57,21 @@ func sliceBoundsCheck64(capacity uintptr, low, high uint64) {
 }
 
 // Check for bounds in *ssa.MakeSlice.
-func sliceBoundsCheckMake(length, capacity uint) {
+func sliceBoundsCheckMake(length, capacity uintptr, elementSizeDoubled uintptr) {
-	if !(0 <= length && length <= capacity) {
+	overflow := uint64(capacity*elementSizeDoubled) != uint64(capacity)*uint64(elementSizeDoubled)
+	if length > capacity || overflow {
 		runtimePanic("slice size out of range")
 	}
 }
 
 // Check for bounds in *ssa.MakeSlice. Supports 64-bit indexes.
-func sliceBoundsCheckMake64(length, capacity uint64) {
+func sliceBoundsCheckMake64(length, capacity uint64, elementSizeDoubled uintptr) {
-	if !(0 <= length && length <= capacity) {
+	// This function is only ever called on systems where uintptr is smaller
+	// than uint64 (thus must be 32-bit or less). So multiplying as uint64 will
+	// never overflow if we know that capacity fits in uintptr.
+	// That elementSizeDoubled fits in uintptr is checked by the compiler.
+	overflow := capacity != uint64(uintptr(capacity)) || capacity != uint64(uintptr(capacity*uint64(elementSizeDoubled)))
+	if length > capacity || overflow {
 		runtimePanic("slice size out of range")
 	}
 }