diff options
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp | 31 |
1 files changed, 18 insertions, 13 deletions
diff --git a/llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp b/llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp index 303986a0b49..c548f36d094 100644 --- a/llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp +++ b/llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp @@ -11,8 +11,7 @@ /// The expectation is that the loop contains three pseudo instructions: /// - t2*LoopStart - placed in the preheader or pre-preheader. The do-loop /// form should be in the preheader, whereas the while form should be in the -/// preheaders only predecessor. TODO: Could DoLoopStart get moved into the -/// pre-preheader? +/// preheaders only predecessor. /// - t2LoopDec - placed within in the loop body. /// - t2LoopEnd - the loop latch terminator. /// @@ -176,19 +175,25 @@ bool ARMLowOverheadLoops::ProcessLoop(MachineLoop *ML) { // faster than performing a sub,cmp,br or even subs,br. Revert = true; - if (!Dec) + if (!Dec || End) continue; - // If we find that we load/store LR between LoopDec and LoopEnd, expect - // that the decremented value has been spilled to the stack. Because - // this value isn't actually going to be produced until the latch, by LE, - // we would need to generate a real sub. The value is also likely to be - // reloaded for use of LoopEnd - in which in case we'd need to perform - // an add because it gets negated again by LE! The other option is to - // then generate the other form of LE which doesn't perform the sub. - if (MI.mayLoad() || MI.mayStore()) - Revert = - MI.getOperand(0).isReg() && MI.getOperand(0).getReg() == ARM::LR; + // If we find that LR has been written or read between LoopDec and + // LoopEnd, expect that the decremented value is being used else where. + // Because this value isn't actually going to be produced until the + // latch, by LE, we would need to generate a real sub. The value is also + // likely to be copied/reloaded for use of LoopEnd - in which in case + // we'd need to perform an add because it gets subtracted again by LE! + // The other option is to then generate the other form of LE which doesn't + // perform the sub. + for (auto &MO : MI.operands()) { + if (MI.getOpcode() != ARM::t2LoopDec && MO.isReg() && + MO.getReg() == ARM::LR) { + LLVM_DEBUG(dbgs() << "ARM Loops: Found LR Use/Def: " << MI); + Revert = true; + break; + } + } } if (Dec && End && Revert) |
