This is a bug, but not an Attributor one ;)

https://godbolt.org/z/vhsKPf

Looking where the attribute needs to be dropped now.

Somewhere in instcombine but I didn't find it immediately, I hope someone knows and gives an update tomorrow.

Thanks for pointing it out. I'll give it a try.

Thanks for pointing it out. I'll give it a try.

It might be as simple as this https://reviews.llvm.org/D87306

I haven't tried it though. We might not need to know where it comes from ;)

Minimal test:

define i32 @​#48810 (i32* %x) {
%r = call dereferenceable(1) i8* @​mempcpy(i8* undef, i32* null, i64 undef)
ret i32 undef
}

declare i8* @​mempcpy(i8*, i32*, i64)

Instcombine tries to convert that to a memcpy intrinsic:

Value *LibCallSimplifier::optimizeMemPCpy(CallInst *CI, IRBuilderBase &B) {
Value *Dst = CI->getArgOperand(0);
Value *N = CI->getArgOperand(2);
// mempcpy(x, y, n) -> llvm.memcpy(align 1 x, align 1 y, n), x + n
CallInst *NewCI =
B.CreateMemCpy(Dst, Align(1), CI->getArgOperand(1), Align(1), N);
NewCI->setAttributes(CI->getAttributes());

But IIUC, we can't apply "dereferenceable" to a void return.

Minimal test:

define i32 @​#48810 (i32* %x) {
%r = call dereferenceable(1) i8* @​mempcpy(i8* undef, i32* null, i64 undef)
ret i32 undef
}

declare i8* @​mempcpy(i8*, i32*, i64)

---

--

Instcombine tries to convert that to a memcpy intrinsic:

Value *LibCallSimplifier::optimizeMemPCpy(CallInst *CI, IRBuilderBase &B) {
Value *Dst = CI->getArgOperand(0);
Value *N = CI->getArgOperand(2);
// mempcpy(x, y, n) -> llvm.memcpy(align 1 x, align 1 y, n), x + n
CallInst *NewCI =
B.CreateMemCpy(Dst, Align(1), CI->getArgOperand(1), Align(1), N);
NewCI->setAttributes(CI->getAttributes());

---

--

But IIUC, we can't apply "dereferenceable" to a void return.

We need something like this (taken from InstCombineCalls.cpp:2281):

    // Get any return attributes.
    AttrBuilder RAttrs(CallerPAL, AttributeList::ReturnIndex);
    
    // If the return value is not being used, the type may not be compatible
    // with the existing attributes.  Wipe out any problematic attributes.
    RAttrs.remove(AttributeFuncs::typeIncompatible(NewRetTy));  

Thanks for the pointer!
Zequan, are you working on this? If not, I can post a patch for review.

No, I am not.
Feel free to post a patch. Thanks

https://reviews.llvm.org/D95088

Minimally fixed the crash:
https://reviews.llvm.org/rG070af1b7887f

Thanks for the quick fix.