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...ibc.so.6(abort+0x10e)[0x2b59c5fb684e] /lib/libc.so.6(__assert_fail+0x104)[0x2b59c5faeaf4] llc[0x7d8149] llc((anonymous namespace)::BranchFolder::ReplaceTailWithBranchTo(llvm::ilist_iterator<llvm::MachineInstr>, llvm::MachineBasicBlock*)+0xe3)[0xab7ef9] llc((anonymous namespace)::BranchFolder::TailMergeBlocks(llvm::MachineFunction&)+0x451)[0xab837b] llc((anonymous namespace)::BranchFolder::runOnMachineFunction(llvm::MachineFunction&)+0x7d)[0xab872d] Best Regards, Rafael

...blem with this section of code is that FallThrough is not guaranteed to be a successor of MBB or even a descendent of MBB. The bitcode I've attached is a case where there are 5 basic blocks, where the first four end with conditional branches to an early return, as specified with initial.dot. TailMergeBlocks in BranchFolding::runOnMachineFunction merges the 4 early return blocks to a single basic block and numbers renumbers them, as specified with tailmerge.dot. When it runs optimize block on the if.end14 block, it enters the above segment of code, removing it and replacing it with FallThrough, which...