LateLowerGCFrame infinite loops in presence of `@llvm.vector.insert` in IR

[Zentrik]

On master this IR hangs in LateLowerGCFrame

; ModuleID = 'reduced.bc'
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128-ni:10:11:12:13"
target triple = "x86_64-unknown-linux-gnu"

declare ptr @julia.get_pgcstack()

define swiftcc void @julia_abstract_modifyopNOT._36663(<4 x ptr addrspace(10)> %0, <2 x ptr addrspace(10)> %1) {
top:
  %pgcstack = call ptr @julia.get_pgcstack()
  %2 = call <4 x ptr addrspace(10)> @llvm.vector.insert.v4p10.v2p10(<4 x ptr addrspace(10)> %0, <2 x ptr addrspace(10)> %1, i64 2)
  ret void
}

The hang is in the FindBaseValue function as this code doesn't seem to handle this intrinsic

julia/src/llvm-late-gc-lowering.cpp

Lines 174 to 179 in 9136bdd

	else if (auto II = dyn_cast<IntrinsicInst>(CurrentV)) {
	// Some intrinsics behave like LoadInst followed by a SelectInst
	// This should never happen in a derived addrspace (since those cannot be stored to memory)
	// so we don't need to lift these operations, but we do need to check if it's loaded and continue walking the base pointer
	if (II->getIntrinsicID() == Intrinsic::masked_load ||
	II->getIntrinsicID() == Intrinsic::masked_gather) {

[Zentrik]

Will be fixed by #55864