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If header of inner loop is aligned, do not align the outer loop header. We don't want to add nops in the outer loop for the sake of aligning the inner loop.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@71609 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2009-05-12 23:58:14 +00:00
parent eca24fba3f
commit 9d3094b38e
2 changed files with 78 additions and 6 deletions
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39
lib/CodeGen/CodePlacementOpt.cpp
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@ -62,6 +62,8 @@ namespace {
private:
bool OptimizeIntraLoopEdges();
bool HeaderShouldBeAligned(MachineBasicBlock *MBB, MachineLoop *L,
SmallPtrSet<MachineBasicBlock*, 4> &DoNotAlign);
bool AlignLoops(MachineFunction &MF);
};
@ -244,14 +246,37 @@ bool CodePlacementOpt::OptimizeIntraLoopEdges() {
/// 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) {
bool
CodePlacementOpt::HeaderShouldBeAligned(MachineBasicBlock *MBB, MachineLoop *L,
SmallPtrSet<MachineBasicBlock*, 4> &DoNotAlign) {
if (DoNotAlign.count(MBB))
return false;
bool BackEdgeBelow = false;
for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
PE = MBB->pred_end(); PI != PE; ++PI) {
MachineBasicBlock *PredMBB = *PI;
if (PredMBB == MBB || PredMBB->getNumber() > MBB->getNumber())
return true;
if (PredMBB == MBB || PredMBB->getNumber() > MBB->getNumber()) {
BackEdgeBelow = true;
break;
}
}
return false;
if (!BackEdgeBelow)
return false;
// Ok, we are going to align this loop header. If it's an inner loop,
// do not align its outer loop.
MachineBasicBlock *PreHeader = L->getLoopPreheader();
if (PreHeader) {
MachineLoop *L = MLI->getLoopFor(PreHeader);
if (L) {
MachineBasicBlock *HeaderBlock = L->getHeader();
HeaderBlock->setAlignment(0);
DoNotAlign.insert(HeaderBlock);
}
}
return true;
}
/// AlignLoops - Align loop headers to target preferred alignments.
@ -269,14 +294,16 @@ bool CodePlacementOpt::AlignLoops(MachineFunction &MF) {
MF.RenumberBlocks();
bool Changed = false;
SmallPtrSet<MachineBasicBlock*, 4> DoNotAlign;
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))
MachineLoop *L = MLI->getLoopFor(HeaderMBB);
if (L == 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)) {
if (HeaderShouldBeAligned(HeaderMBB, L, DoNotAlign)) {
HeaderMBB->setAlignment(Align);
Changed = true;
++NumHeaderAligned;