interp: better support interface operations

This commit teaches the interp scanner that supported interface
operations (type assertions, interface assertions) are supported.

This fixes a problem with math/rand in Go 1.14.

interp/scan.go

@@ -51,6 +51,8 @@ func (e *evalPackage) hasSideEffects(fn llvm.Value) (*sideEffectResult, error) {
 		return &sideEffectResult{severity: sideEffectNone}, nil
 	case name == "runtime._panic":
 		return &sideEffectResult{severity: sideEffectLimited}, nil
+	case name == "runtime.typeAssert":
+		return &sideEffectResult{severity: sideEffectNone}, nil
 	case name == "runtime.interfaceImplements":
 		return &sideEffectResult{severity: sideEffectNone}, nil
 	case name == "runtime.sliceCopy":
@@ -118,6 +120,12 @@ func (e *evalPackage) hasSideEffects(fn llvm.Value) (*sideEffectResult, error) {
 				if child.IsDeclaration() {
 					// External function call. Assume only limited side effects
 					// (no affected globals, etc.).
+					switch child.Name() {
+					case "runtime.typeAssert":
+						continue // implemented in interp
+					case "runtime.interfaceImplements":
+						continue // implemented in interp
+					}
 					if e.hasLocalSideEffects(dirtyLocals, inst) {
 						result.updateSeverity(sideEffectLimited)
 					}

interp/scan_test.go

@@ -23,6 +23,8 @@ var scanTestTable = []struct {
 	{"callFunctionPointer", sideEffectAll, []string{"functionPointer"}},
 	{"getDirtyPointer", sideEffectLimited, nil},
 	{"storeToPointer", sideEffectLimited, nil},
+	{"callTypeAssert", sideEffectNone, nil},
+	{"callInterfaceImplements", sideEffectNone, nil},
 }
 
 func TestScan(t *testing.T) {

interp/testdata/scan.ll

@@ -1,6 +1,11 @@
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64--linux"
 
+%runtime.typecodeID = type { %runtime.typecodeID*, i64 }
+
+declare i1 @runtime.typeAssert(i64, %runtime.typecodeID*, i8*, i8*)
+declare i1 @runtime.interfaceImplements(i64, i8**)
+
 define i64 @returnsConst() {
   ret i64 0
 }
@@ -59,3 +64,15 @@ define i64 @callFunctionPointer() {
   %result = call i64 %fp()
   ret i64 %result
 }
+
+define i1 @callTypeAssert() {
+  ; Note: parameters are not realistic.
+  %ok = call i1 @runtime.typeAssert(i64 0, %runtime.typecodeID* null, i8* undef, i8* null)
+  ret i1 %ok
+}
+
+define i1 @callInterfaceImplements() {
+  ; Note: parameters are not realistic.
+  %ok = call i1 @runtime.interfaceImplements(i64 0, i8** null)
+  ret i1 %ok
+}