From 0269d3cbf37227c48b7ce0f9710f0c6a15ff6fa9 Mon Sep 17 00:00:00 2001 From: Evan Cheng Date: Fri, 8 May 2009 19:01:44 +0000 Subject: 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 --- lib/CodeGen/CodePlacementOpt.cpp | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/lib/CodeGen/CodePlacementOpt.cpp b/lib/CodeGen/CodePlacementOpt.cpp index 4276651..1848378 100644 --- a/lib/CodeGen/CodePlacementOpt.cpp +++ b/lib/CodeGen/CodePlacementOpt.cpp @@ -249,6 +249,20 @@ bool CodePlacementOpt::OptimizeIntraLoopEdges() { return Changed; } +/// HeaderShouldBeAligned - Return true if the specified loop header block +/// should be aligned. For now, we will not align it if all the predcessors +/// (i.e. loop back edges) are laid out above the header. FIXME: Do not +/// align small loops. +static bool HeaderShouldBeAligned(MachineBasicBlock *MBB) { + for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(), + PE = MBB->pred_end(); PI != PE; ++PI) { + MachineBasicBlock *PredMBB = *PI; + if (PredMBB->getNumber() > MBB->getNumber()) + return true; + } + return false; +} + /// AlignLoops - Align loop headers to target preferred alignments. /// bool CodePlacementOpt::AlignLoops(MachineFunction &MF) { @@ -267,9 +281,11 @@ bool CodePlacementOpt::AlignLoops(MachineFunction &MF) { for (unsigned i = 0, e = LoopHeaders.size(); i != e; ++i) { MachineBasicBlock *HeaderMBB = LoopHeaders[i]; MachineBasicBlock *PredMBB = prior(MachineFunction::iterator(HeaderMBB)); - if (MLI->getLoopFor(HeaderMBB) != MLI->getLoopFor(PredMBB)) { + if (MLI->getLoopFor(HeaderMBB) == MLI->getLoopFor(PredMBB)) // If previously BB is in the same loop, don't align this BB. We want // to prevent adding noop's inside a loop. + continue; + if (HeaderShouldBeAligned(HeaderMBB)) { HeaderMBB->setAlignment(Align); Changed = true; ++NumHeaderAligned; -- cgit v1.1