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IR/Verifier: Do not allow kernel to kernel calls. #144445

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IR/Verifier: Do not allow kernel to kernel calls. #144445

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IR/Verifier: Do not allow kernel to kernel calls.
jofrn Jun 16, 2025
1f46318
Merge rules together.
jofrn Jun 17, 2025
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5 changes: 4 additions & 1 deletion llvm/lib/IR/Verifier.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3632,8 +3632,11 @@ void Verifier::visitCallBase(CallBase &Call) {
Check(Callee->getValueType() == FTy,
"Intrinsic called with incompatible signature", Call);

// Find the actual CC of the callee from the Module.
CallingConv::ID CalleeCC = Call.getParent()->getParent()->getParent()
->getFunction(Call.getCalledFunction()->getName())->getCallingConv();
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This is a very complicated way to spell Callee->getCallingConv() -- but note that Callee may be null here for indirect calls -- which is the cause of your four thousand or so test failures.

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@jofrn jofrn Jun 17, 2025 •
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Right, it is, but we can have a call of the function without its CC specified. If its definition has a kernel CC, then the callsite may be treated as requiring the definition when it does not have it. If the Verifier checks from the module, then we will not error out in a location that requires the callsite to have the CC at its definition; we will error in the Verifier instead.

// Verify if the calling convention of the callee is callable.
Check(isCallableCC(Call.getCallingConv()),
Check(isCallableCC(CalleeCC),
"calling convention does not permit calls", Call);

// Disallow passing/returning values with alignment higher than we can
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9 changes: 9 additions & 0 deletions llvm/test/Verifier/AMDGPU/kernel-recursivecall.ll
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@@ -0,0 +1,9 @@
; RUN: not llvm-as %s -disable-output 2>&1 | FileCheck %s

define amdgpu_kernel void @kernel(ptr addrspace(1) %out, i32 %n) {
entry:
; CHECK: calling convention does not permit calls
; CHECK-NEXT: call void @kernel(ptr addrspace(1) %out, i32 %n)
call void @kernel(ptr addrspace(1) %out, i32 %n)
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@shiltian shiltian Jun 17, 2025 •
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This IR is malformed in the first place because it doesn't use the right CC for the callee.

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@jofrn jofrn Jun 17, 2025 •
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It ends up getting the same error as your other one "Mark entry as invalid" if we do not have the CC match though, so it would be better to have this error in the Verifier.

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I think we should deal with this in codegen. From an IR perspective, nothing is structurally wrong. Codegen should still be able to set up a call to the kernel as-if it were a callable function

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I don't think it'd be a good idea. It will break a lot of assumptions and conventions we have for kernel function.

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No it doesn't. This is still a UB call that can be treated as a no-op

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Codegen should still be able to set up a call to the kernel as-if it were a callable function

Wouldn't this rely on Codegen retrieving the CC from the module as well?

ret void
}
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