From 2f57e4ff6dbbe176e065c104e2f419be2b21dd9f Mon Sep 17 00:00:00 2001
From: Nia Waldvogel <niaow1234@gmail.com>
Date: Thu, 13 Jan 2022 13:41:55 -0500
Subject: [PATCH] interp: handle type assertions on nil interfaces

Previously, a type assertion on a nil interface would result in an out-of-bounds operand access, as we assumed it was a ptrtoint.
This would usually result in an undefined value which happens not to have the same name as the asserted type (and therefore the assertion fails as expected).
However, with an LLVM build with asserts, LLVM throws an assertion error:
```
interp.test: /home/niaow/go/src/github.com/tinygo-org/tinygo/llvm-project/llvm/include/llvm/IR/User.h:170: llvm::Value* llvm::User::getOperand(unsigned int) const: Assertion `i < NumUserOperands && "getOperand() out of range!"' failed.
```

This change handles a type code of 0 specially.
---
 interp/interpreter.go            | 4 ++++
 interp/testdata/interface.ll     | 3 +++
 interp/testdata/interface.out.ll | 1 +
 3 files changed, 8 insertions(+)

diff --git a/interp/interpreter.go b/interp/interpreter.go
index 64bb060d..ece8b257 100644
--- a/interp/interpreter.go
+++ b/interp/interpreter.go
@@ -388,6 +388,10 @@ func (r *runner) run(fn *function, params []value, parentMem *memoryView, indent
 				if err != nil {
 					return nil, mem, r.errorAt(inst, err)
 				}
+				if !actualTypePtrToInt.IsAConstantInt().IsNil() && actualTypePtrToInt.ZExtValue() == 0 {
+					locals[inst.localIndex] = literalValue{uint8(0)}
+					break
+				}
 				actualType := actualTypePtrToInt.Operand(0)
 				if strings.TrimPrefix(actualType.Name(), "reflect/types.type:") == strings.TrimPrefix(assertedType.Name(), "reflect/types.typeid:") {
 					locals[inst.localIndex] = literalValue{uint8(1)}
diff --git a/interp/testdata/interface.ll b/interp/testdata/interface.ll
index 060256d2..6520efc5 100644
--- a/interp/testdata/interface.ll
+++ b/interp/testdata/interface.ll
@@ -5,6 +5,7 @@ target triple = "x86_64--linux"
 %runtime.interfaceMethodInfo = type { i8*, i64 }
 
 @main.v1 = global i1 0
+@main.v2 = global i1 0
 @"reflect/types.type:named:main.foo" = private constant %runtime.typecodeID { %runtime.typecodeID* @"reflect/types.type:basic:int", i64 0, %runtime.interfaceMethodInfo* null }
 @"reflect/types.typeid:named:main.foo" = external constant i8
 @"reflect/types.type:basic:int" = external constant %runtime.typecodeID
@@ -23,5 +24,7 @@ entry:
   ; Test type asserts.
   %typecode = call i1 @runtime.typeAssert(i64 ptrtoint (%runtime.typecodeID* @"reflect/types.type:named:main.foo" to i64), i8* @"reflect/types.typeid:named:main.foo", i8* undef, i8* null)
   store i1 %typecode, i1* @main.v1
+  %typecode2 = call i1 @runtime.typeAssert(i64 0, i8* @"reflect/types.typeid:named:main.foo", i8* undef, i8* null)
+  store i1 %typecode2, i1* @main.v2
   ret void
 }
diff --git a/interp/testdata/interface.out.ll b/interp/testdata/interface.out.ll
index 2d2467b6..1fb9249b 100644
--- a/interp/testdata/interface.out.ll
+++ b/interp/testdata/interface.out.ll
@@ -2,6 +2,7 @@ target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64--linux"
 
 @main.v1 = local_unnamed_addr global i1 true
+@main.v2 = local_unnamed_addr global i1 false
 
 define void @runtime.initAll() unnamed_addr {
 entry: