错误信息:
Assertion failed: HasHungOffUses && "alloc must have hung off uses", file I:\GitHub\Def\llvm\lib\IR\User.cpp, line 44
有人踩过这个坑没?
内存监视什么的都用了,debug了三天,LLVM 文档也翻遍了,找不到问题所在啊摔!
源代码:
/**
* if 条件分支
*/
Value* ASTIf::codegen(Gen & gen)
{
// if 节点返回值
Value *v_ret(nullptr);
auto *thefunc = gen.builder.GetInsertBlock()->getParent();
Value *v_cond = cond->codegen(gen);
auto *b_then = BasicBlock::Create(gen.context, "then", thefunc);
auto *b_else = BasicBlock::Create(gen.context, "else", thefunc);
auto *b_merge = BasicBlock::Create(gen.context, "ifcont", thefunc);
// 跳转分支
gen.builder.CreateCondBr(v_cond, b_then, b_else);
// then block
gen.builder.SetInsertPoint(b_then);
Value *v_then = pthen->codegen(gen);
gen.builder.CreateBr(b_merge);
b_then = gen.builder.GetInsertBlock();
// else block
gen.builder.SetInsertPoint(b_else);
Value *v_else = pelse ? pelse->codegen(gen) : nullptr;
gen.builder.CreateBr(b_merge);
b_else = gen.builder.GetInsertBlock();
// merge block
gen.builder.SetInsertPoint(b_merge);
// if 分支类型一致 HasHungOffUses
if (canphi) {
PHINode *phi = gen.builder.CreatePHI( // 【【【报错行!!!】】】
v_then->getType(), 2, "iftmp");
phi->addIncoming(v_then, b_then);
phi->addIncoming(v_else, b_else);
v_ret = phi;
}
return v_ret;
}
如果实在不行就关掉Assertion,LLVM默认编译是Release+Assert版本的,有一个选项“--disable-assert”什么,具体记不太清楚了,编个纯realse版本的,就没有assert失败了,哈哈哈
TR;DL:
请关闭VS的sdl检查
这个assert检查的是一个在operator new里设置的内存标志位HasHungOffUses,sdl检查会导致默认构造函数的行为改变,清零new出来的内存空间导致标志位错误。
我在VS2015U2下手动创建项目、设置依赖试了一下,不仅仅是Def的有问题,连Kaleidoscope-Ch8(LLVM的官方示例)调用这个都会出问题。然而我注意到LLVM项目自带的example项目里编译出来的是没问题的。我马上想到了编译选项的问题,经过漫长的测试后得出的结论是:
gen.builder.CreatePHI最终调用了User::operator new,
void *User::operator new(size_t Size) {
// Allocate space for a single Use*
void *Storage = ::operator new(Size + sizeof(Use *));
Use **HungOffOperandList = static_cast<Use **>(Storage);
User *Obj = reinterpret_cast<User *>(HungOffOperandList + 1);
Obj->NumUserOperands = 0;
Obj->HasHungOffUses = true;
Obj->HasDescriptor = false;
*HungOffOperandList = nullptr;
return Obj;
}
Obj->HasHungOffUses = true;就是设置了这个标志位,用来标志内存空间的分配情况。
而PHINode的构造函数中,调用了allocHungoffUses,在User::allocHungoffUses中就会检查这个标志位来确认内存的分配
explicit PHINode(Type *Ty, unsigned NumReservedValues,
const Twine &NameStr = "",
Instruction *InsertBefore = nullptr)
: Instruction(Ty, Instruction::PHI, nullptr, 0, InsertBefore),
ReservedSpace(NumReservedValues) {
setName(NameStr);
allocHungoffUses(ReservedSpace);
}
//………………
void User::allocHungoffUses(unsigned N, bool IsPhi) {
assert(HasHungOffUses && "alloc must have hung off uses");
static_assert(AlignOf<Use>::Alignment >= AlignOf<Use::UserRef>::Alignment,
"Alignment is insufficient for 'hung-off-uses' pieces");
static_assert(AlignOf<Use::UserRef>::Alignment >=
AlignOf<BasicBlock *>::Alignment,
"Alignment is insufficient for 'hung-off-uses' pieces");
// Allocate the array of Uses, followed by a pointer (with bottom bit set) to
// the User.
size_t size = N * sizeof(Use) + sizeof(Use::UserRef);
if (IsPhi)
size += N * sizeof(BasicBlock *);
Use *Begin = static_cast<Use*>(::operator new(size));
Use *End = Begin + N;
(void) new(End) Use::UserRef(const_cast<User*>(this), 1);
setOperandList(Use::initTags(Begin, End));
}
如果开启了sdl,调用构造函数前该对象的内存空间疑似会被清零,导致HasHungOffUses的值错误的设置成false,assert失败。