Verena Beckham
2013-Jul-22 16:18 UTC
[LLVMdev] Predication bug in AggressiveAntiDepBreaker?
Hi, I wondered whether the AggressiveAntiDepBreaker can properly handle predicated instructions. At the end of PrescanInstruction the "DefIndices" array is updated with the destination register without checking whether the instruction is predicated. That shortens the live range: Later on, in HandleLastUse we check whether the register IsLive, which considers only "KillIndices" and "DefIndices", and therefore returns False for the interval between the predicated instruction and any non-predicated read before it. So that read is considered the last use. In my example this leads to a register not being fully renamed everywhere. I don't think a predicated write should count as a define. The attached patch fixes this test case. Or am I missing something target dependent here? -- Verena Beckham Vice President Engineering Codeplay Software Ltd 45 York Place, Edinburgh, EH1 3HP Tel: 0131 466 0503 Fax: 0131 557 6600 Website: http://www.codeplay.com This email and any attachments may contain confidential and /or privileged information and is for use by the addressee only. If you are not the intended recipient, please notify Codeplay Software Ltd immediately and delete the message from your computer. You may not copy or forward it,or use or disclose its contents to any other person. Any views or other information in this message which do not relate to our business are not authorized by Codeplay software Ltd, nor does this message form part of any contract unless so stated. As internet communications are capable of data corruption Codeplay Software Ltd does not accept any responsibility for any changes made to this message after it was sent. Please note that Codeplay Software Ltd does not accept any liability or responsibility for viruses and it is your responsibility to scan any attachments. Company registered in England and Wales, number: 04567874 Registered office: 81 Linkfield Street, Redhill RH1 6BY -------------- next part -------------- Index: AggressiveAntiDepBreaker.cpp ==================================================================--- AggressiveAntiDepBreaker.cpp (revision 186828) +++ AggressiveAntiDepBreaker.cpp (working copy) @@ -399,7 +399,7 @@ unsigned Reg = MO.getReg(); if (Reg == 0) continue; // Ignore KILLs and passthru registers for liveness... - if (MI->isKill() || (PassthruRegs.count(Reg) != 0)) + if (MI->isKill() || (PassthruRegs.count(Reg) != 0) || TII->isPredicated(MI)) continue; // Update def for Reg and aliases.