From 1872096f1e2befed2a3be6617eddfb18a06f80d7 Mon Sep 17 00:00:00 2001 From: "Duncan P. N. Exon Smith" Date: Sun, 11 Sep 2016 18:51:28 +0000 Subject: CodeGen: Give MachineBasicBlock::reverse_iterator a handle to the current MI Now that MachineBasicBlock::reverse_instr_iterator knows when it's at the end (since r281168 and r281170), implement MachineBasicBlock::reverse_iterator directly on top of an ilist::reverse_iterator by adding an IsReverse template parameter to MachineInstrBundleIterator. This replaces another hard-to-reason-about use of std::reverse_iterator on list iterators, matching the changes for ilist::reverse_iterator from r280032 (see the "out of scope" section at the end of that commit message). MachineBasicBlock::reverse_iterator now has a handle to the current node and has obvious invalidation semantics. r280032 has a more detailed explanation of how list-style reverse iterators (invalidated when the pointed-at node is deleted) are different from vector-style reverse iterators like std::reverse_iterator (invalidated on every operation). A great motivating example is this commit's changes to lib/CodeGen/DeadMachineInstructionElim.cpp. Note: If your out-of-tree backend deletes instructions while iterating on a MachineBasicBlock::reverse_iterator or converts between MachineBasicBlock::iterator and MachineBasicBlock::reverse_iterator, you'll need to update your code in similar ways to r280032. The following table might help: [Old] ==> [New] delete &*RI, RE = end() delete &*RI++ RI->erase(), RE = end() RI++->erase() reverse_iterator(I) std::prev(I).getReverse() reverse_iterator(I) ++I.getReverse() --reverse_iterator(I) I.getReverse() reverse_iterator(std::next(I)) I.getReverse() RI.base() std::prev(RI).getReverse() RI.base() ++RI.getReverse() --RI.base() RI.getReverse() std::next(RI).base() RI.getReverse() (For more details, have a look at r280032.) llvm-svn: 281172 --- llvm/lib/CodeGen/DeadMachineInstructionElim.cpp | 9 +-------- 1 file changed, 1 insertion(+), 8 deletions(-) (limited to 'llvm/lib/CodeGen/DeadMachineInstructionElim.cpp') diff --git a/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp b/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp index 0b8dc7a86ad..17c229a216a 100644 --- a/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp +++ b/llvm/lib/CodeGen/DeadMachineInstructionElim.cpp @@ -122,7 +122,7 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) { // liveness as we go. for (MachineBasicBlock::reverse_iterator MII = MBB.rbegin(), MIE = MBB.rend(); MII != MIE; ) { - MachineInstr *MI = &*MII; + MachineInstr *MI = &*MII++; // If the instruction is dead, delete it! if (isDead(MI)) { @@ -133,9 +133,6 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) { MI->eraseFromParentAndMarkDBGValuesForRemoval(); AnyChanges = true; ++NumDeletes; - MIE = MBB.rend(); - // MII is now pointing to the next instruction to process, - // so don't increment it. continue; } @@ -169,10 +166,6 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) { } } } - - // We didn't delete the current instruction, so increment MII to - // the next one. - ++MII; } } -- cgit v1.2.3