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Don't align loop header unless the loop back edge is below the header. 

llvm-svn: 71242
This commit is contained in:
Evan Cheng 2009-05-08 19:01:44 +00:00
parent 65a58168cc
commit 6e9959e327
1 changed files with 17 additions and 1 deletions
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18
llvm/lib/CodeGen/CodePlacementOpt.cpp
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@ -249,6 +249,20 @@ bool CodePlacementOpt::OptimizeIntraLoopEdges() {
return Changed; 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. /// AlignLoops - Align loop headers to target preferred alignments.
/// ///
bool CodePlacementOpt::AlignLoops(MachineFunction &MF) { bool CodePlacementOpt::AlignLoops(MachineFunction &MF) {
@ -267,9 +281,11 @@ bool CodePlacementOpt::AlignLoops(MachineFunction &MF) {
for (unsigned i = 0, e = LoopHeaders.size(); i != e; ++i) { for (unsigned i = 0, e = LoopHeaders.size(); i != e; ++i) {
MachineBasicBlock *HeaderMBB = LoopHeaders[i]; MachineBasicBlock *HeaderMBB = LoopHeaders[i];
MachineBasicBlock *PredMBB = prior(MachineFunction::iterator(HeaderMBB)); 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 // If previously BB is in the same loop, don't align this BB. We want
// to prevent adding noop's inside a loop. // to prevent adding noop's inside a loop.
continue;
if (HeaderShouldBeAligned(HeaderMBB)) {
HeaderMBB->setAlignment(Align); HeaderMBB->setAlignment(Align);
Changed = true; Changed = true;
++NumHeaderAligned; ++NumHeaderAligned;