compiler: implement recover() built-in function

compiler/calls.go

@@ -33,17 +33,36 @@ const (
 	paramIsDeferenceableOrNull = 1 << iota
 )
 
-// createCall creates a new call to runtime.<fnName> with the given arguments.
-func (b *builder) createRuntimeCall(fnName string, args []llvm.Value, name string) llvm.Value {
+// createRuntimeCallCommon creates a runtime call. Use createRuntimeCall or
+// createRuntimeInvoke instead.
+func (b *builder) createRuntimeCallCommon(fnName string, args []llvm.Value, name string, isInvoke bool) llvm.Value {
 	fn := b.program.ImportedPackage("runtime").Members[fnName].(*ssa.Function)
 	llvmFn := b.getFunction(fn)
 	if llvmFn.IsNil() {
 		panic("trying to call non-existent function: " + fn.RelString(nil))
 	}
 	args = append(args, llvm.Undef(b.i8ptrType)) // unused context parameter
+	if isInvoke {
+		return b.createInvoke(llvmFn, args, name)
+	}
 	return b.createCall(llvmFn, args, name)
 }
 
+// createRuntimeCall creates a new call to runtime.<fnName> with the given
+// arguments.
+func (b *builder) createRuntimeCall(fnName string, args []llvm.Value, name string) llvm.Value {
+	return b.createRuntimeCallCommon(fnName, args, name, false)
+}
+
+// createRuntimeInvoke creates a new call to runtime.<fnName> with the given
+// arguments. If the runtime call panics, control flow is diverted to the
+// landing pad block.
+// Note that "invoke" here is meant in the LLVM sense (a call that can
+// panic/throw), not in the Go sense (an interface method call).
+func (b *builder) createRuntimeInvoke(fnName string, args []llvm.Value, name string) llvm.Value {
+	return b.createRuntimeCallCommon(fnName, args, name, true)
+}
+
 // createCall creates a call to the given function with the arguments possibly
 // expanded.
 func (b *builder) createCall(fn llvm.Value, args []llvm.Value, name string) llvm.Value {
@@ -55,6 +74,15 @@ func (b *builder) createCall(fn llvm.Value, args []llvm.Value, name string) llvm
 	return b.CreateCall(fn, expanded, name)
 }
 
+// createInvoke is like createCall but continues execution at the landing pad if
+// the call resulted in a panic.
+func (b *builder) createInvoke(fn llvm.Value, args []llvm.Value, name string) llvm.Value {
+	if b.hasDeferFrame() {
+		b.createInvokeCheckpoint()
+	}
+	return b.createCall(fn, args, name)
+}
+
 // Expand an argument type to a list that can be used in a function call
 // parameter list.
 func (c *compilerContext) expandFormalParamType(t llvm.Type, name string, goType types.Type) []paramInfo {