compiler, runtime: make slice lookup panics recoverable

Author: aykevl

GNUmakefile

@@ -383,6 +383,7 @@ TEST_PACKAGES_LINUX := \
 	crypto/hmac \
 	debug/dwarf \
 	debug/plan9obj \
+	encoding/binary \
 	go/constant \
 	image \
 	io/ioutil \
@@ -406,6 +407,7 @@ TEST_PACKAGES_WINDOWS := \
 	compress/flate \
 	crypto/des \
 	crypto/hmac \
+	encoding/binary \
 	go/constant \
 	math/bits \
 	strconv \

compiler/asserts.go

@@ -31,7 +31,7 @@ func (b *builder) createLookupBoundsCheck(arrayLen, index llvm.Value) {
 
 	// Now do the bounds check: index >= arrayLen
 	outOfBounds := b.CreateICmp(llvm.IntUGE, index, arrayLen, "")
-	b.createRuntimeAssert(outOfBounds, "lookup", "lookupPanic", false)
+	b.createRuntimeAssert(outOfBounds, "lookup", "lookupPanic", true)
 }
 
 // createSliceBoundsCheck emits a bounds check before a slicing operation to make
@@ -230,7 +230,7 @@ func (b *builder) createDivideByZeroCheck(y llvm.Value) {
 
 // createRuntimeAssert is a common function to create a new branch on an assert
 // bool, calling an assert func if the assert value is true (1).
-func (b *builder) createRuntimeAssert(assert llvm.Value, blockPrefix, assertFunc string, invoke bool) {
+func (b *builder) createRuntimeAssert(assert llvm.Value, blockPrefix, assertFunc string, isInvoke bool) {
 	// Check whether we can resolve this check at compile time.
 	if !assert.IsAConstantInt().IsNil() {
 		val := assert.ZExtValue()
@@ -245,23 +245,17 @@ func (b *builder) createRuntimeAssert(assert llvm.Value, blockPrefix, assertFunc
 	// current insert position.
 	faultBlock := b.ctx.AddBasicBlock(b.llvmFn, blockPrefix+".throw")
 	nextBlock := b.insertBasicBlock(blockPrefix + ".next")
-	b.blockExits[b.currentBlock] = nextBlock // adjust outgoing block for phi nodes
 
 	// Now branch to the out-of-bounds or the regular block.
 	b.CreateCondBr(assert, faultBlock, nextBlock)
 
 	// Fail: the assert triggered so panic.
 	b.SetInsertPointAtEnd(faultBlock)
-	if invoke {
-		// This runtime panic is recoverable.
-		b.createRuntimeInvoke(assertFunc, nil, "")
-	} else {
-		// This runtime panic is not recoverable.
-		b.createRuntimeCall(assertFunc, nil, "")
-	}
+	b.createRuntimeCallCommon(assertFunc, nil, "", isInvoke)
 	b.CreateUnreachable()
 
 	// Ok: assert didn't trigger so continue normally.
+	b.blockExits[b.currentBlock] = nextBlock // adjust outgoing block for phi nodes
 	b.SetInsertPointAtEnd(nextBlock)
 }
 

src/runtime/error.go

@@ -21,5 +21,6 @@ func (r runtimeError) RuntimeError() {}
 
 var (
 	divideError   error = runtimeError{"runtime error: integer divide by zero"}
+	lookupError   error = runtimeError{"runtime error: index out of range"}
 	overflowError error = runtimeError{"runtime error: integer overflow"}
 )

src/runtime/panic.go

@@ -187,7 +187,7 @@ func nilMapPanic() {
 
 // Panic when trying to access an array or slice out of bounds.
 func lookupPanic() {
-	runtimePanicAt(returnAddress(0), "index out of range")
+	_panic(lookupError)
 }
 
 // Panic when trying to slice a slice out of bounds.

testdata/recover.go

@@ -32,6 +32,7 @@ func main() {
 
 	println("\n# runtime panics")
 	runtimePanicDivByZero(1, 0)
+	runtimePanicLookup([]int{1, 2, 3}, 10)
 
 	println("\n# runtime.Goexit")
 	runtimeGoexit()
@@ -127,6 +128,16 @@ func runtimePanicDivByZero(a, b int) int {
 	return a / b
 }
 
+func runtimePanicLookup(slice []int, index int) int {
+	defer func() {
+		if err := recover(); err != nil {
+			println("recovered:", err)
+		}
+	}()
+
+	return slice[index]
+}
+
 func runtimeGoexit() {
 	wg.Add(1)
 	go func() {