Method createChanBoundsCheck

compiler/asserts.go:126–159

createChanBoundsCheck creates a bounds check before creating a new channel to check that the value is not too big for runtime.chanMake.

(elementSize uint64, bufSize llvm.Value, bufSizeType *types.Basic, pos token.Pos)

// createChanBoundsCheck creates a bounds check before creating a new channel to
// check that the value is not too big for runtime.chanMake.
func (b *builder) createChanBoundsCheck(elementSize uint64, bufSize llvm.Value, bufSizeType *types.Basic, pos token.Pos) {
	if b.info.nobounds {
		// The //go:nobounds pragma was added to the function to avoid bounds
		// checking.
		return
	}

	// Make sure bufSize is at least as big as maxBufSize (an uintptr).
	bufSize = b.extendInteger(bufSize, bufSizeType, b.uintptrType)

	// Calculate (^uintptr(0)) >> 1, which is the max value that fits in an
	// uintptr if uintptrs were signed.
	maxBufSize := b.CreateLShr(llvm.ConstNot(llvm.ConstInt(b.uintptrType, 0, false)), llvm.ConstInt(b.uintptrType, 1, false), "")
	if elementSize > maxBufSize.ZExtValue() {
		b.addError(pos, fmt.Sprintf("channel element type is too big (%v bytes)", elementSize))
		return
	}
	// Avoid divide-by-zero.
	if elementSize == 0 {
		elementSize = 1
	}
	// Make the maxBufSize actually the maximum allowed value (in number of
	// elements in the channel buffer).
	maxBufSize = b.CreateUDiv(maxBufSize, llvm.ConstInt(b.uintptrType, elementSize, false), "")

	// Make sure maxBufSize has the same type as bufSize.
	if maxBufSize.Type() != bufSize.Type() {
		maxBufSize = b.CreateZExt(maxBufSize, bufSize.Type(), "")
	}

	// Do the check for a too large (or negative) buffer size.
	bufSizeTooBig := b.CreateICmp(llvm.IntUGE, bufSize, maxBufSize, "")
	b.createRuntimeAssert(bufSizeTooBig, "chan", "chanMakePanic")
}

// createNilCheck checks whether the given pointer is nil, and panics if it is.
// It has no effect in well-behaved programs, but makes sure no uncaught nil