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Don't align loop header unless the loop back edge is below the header.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@71242 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -249,6 +249,20 @@ bool CodePlacementOpt::OptimizeIntraLoopEdges() {
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return Changed;
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}
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/// HeaderShouldBeAligned - Return true if the specified loop header block
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/// should be aligned. For now, we will not align it if all the predcessors
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/// (i.e. loop back edges) are laid out above the header. FIXME: Do not
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/// align small loops.
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static bool HeaderShouldBeAligned(MachineBasicBlock *MBB) {
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for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
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PE = MBB->pred_end(); PI != PE; ++PI) {
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MachineBasicBlock *PredMBB = *PI;
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if (PredMBB->getNumber() > MBB->getNumber())
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return true;
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}
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return false;
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}
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/// AlignLoops - Align loop headers to target preferred alignments.
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///
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bool CodePlacementOpt::AlignLoops(MachineFunction &MF) {
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@ -267,9 +281,11 @@ bool CodePlacementOpt::AlignLoops(MachineFunction &MF) {
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for (unsigned i = 0, e = LoopHeaders.size(); i != e; ++i) {
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MachineBasicBlock *HeaderMBB = LoopHeaders[i];
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MachineBasicBlock *PredMBB = prior(MachineFunction::iterator(HeaderMBB));
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if (MLI->getLoopFor(HeaderMBB) != MLI->getLoopFor(PredMBB)) {
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if (MLI->getLoopFor(HeaderMBB) == MLI->getLoopFor(PredMBB))
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// If previously BB is in the same loop, don't align this BB. We want
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// to prevent adding noop's inside a loop.
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continue;
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if (HeaderShouldBeAligned(HeaderMBB)) {
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HeaderMBB->setAlignment(Align);
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Changed = true;
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++NumHeaderAligned;
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