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LoopRotation: Make the brute force DomTree update more brute force.

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We update until we hit a fixpoint. This is probably slow but also
slightly simplifies the code. It should also fix the occasional
invalid domtrees observed when building with expensive checking.

I couldn't find a case where this had a measurable slowdown, but
if someone finds a pathological case where it does we may have
to find a cleverer way of updating dominators here.

Thanks to Duncan for the test case.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163091 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2012-09-02 11:57:22 +00:00
parent 43bf70986b
commit 7de7078933
2 changed files with 56 additions and 31 deletions
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51
lib/Transforms/Scalar/LoopRotation.cpp
View File

@ -453,41 +453,30 @@ bool LoopRotate::rotateLoop(Loop *L) {
// findNearestCommonDominator on all CFG predecessors of each child of the
// original header.
DomTreeNode *OrigHeaderNode = DT->getNode(OrigHeader);
SmallVector<DomTreeNode *, 8> WorkList(OrigHeaderNode->begin(),
OrigHeaderNode->end());
while (!WorkList.empty()) {
DomTreeNode *Node = WorkList.pop_back_val();
BasicBlock *BB = Node->getBlock();
BasicBlock *NearestDom = 0;
for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;
++PI) {
BasicBlock *Pred = *PI;
SmallVector<DomTreeNode *, 8> HeaderChildren(OrigHeaderNode->begin(),
OrigHeaderNode->end());
bool Changed;
do {
Changed = false;
for (unsigned I = 0, E = HeaderChildren.size(); I != E; ++I) {
DomTreeNode *Node = HeaderChildren[I];
BasicBlock *BB = Node->getBlock();
// We have to process predecessors of a node before we touch the
// actual node. If one of the predecessors is in our worklist, put it
// and the currently processed node on the worklist and go processing
// the predecessor.
SmallVectorImpl<DomTreeNode *>::iterator I =
std::find(WorkList.begin(), WorkList.end(), DT->getNode(Pred));
if (I != WorkList.end()) {
WorkList.push_back(Node);
std::swap(*I, WorkList.back());
// The predecessor is now at the end of the worklist.
NearestDom = 0;
break;
pred_iterator PI = pred_begin(BB);
BasicBlock *NearestDom = *PI;
for (pred_iterator PE = pred_end(BB); PI != PE; ++PI)
NearestDom = DT->findNearestCommonDominator(NearestDom, *PI);
// Remember if this changes the DomTree.
if (Node->getIDom()->getBlock() != NearestDom) {
DT->changeImmediateDominator(BB, NearestDom);
Changed = true;
}
// On the first iteration start with Pred, on the other iterations we
// narrow it down to the nearest common dominator.
if (!NearestDom)
NearestDom = Pred;
else
NearestDom = DT->findNearestCommonDominator(NearestDom, Pred);
}
if (NearestDom)
DT->changeImmediateDominator(BB, NearestDom);
}
// If the dominator changed, this may have an effect on other
// predecessors, continue until we reach a fixpoint.
} while (Changed);
}
}

36
test/Transforms/LoopRotate/multiple-exits.ll
View File

@ -198,3 +198,39 @@ declare i32 @llvm.eh.typeid.for(i8*) nounwind readnone
declare i8* @__cxa_begin_catch(i8*)
declare void @__cxa_end_catch()
define void @test4() nounwind uwtable {
entry:
br label %"7"
"3": ; preds = %"7"
br i1 undef, label %"31", label %"4"
"4": ; preds = %"3"
%. = select i1 undef, float 0x3F50624DE0000000, float undef
%0 = add i32 %1, 1
br label %"7"
"7": ; preds = %"4", %entry
%1 = phi i32 [ %0, %"4" ], [ 0, %entry ]
%2 = icmp slt i32 %1, 100
br i1 %2, label %"3", label %"8"
"8": ; preds = %"7"
br i1 undef, label %"9", label %"31"
"9": ; preds = %"8"
br label %"33"
"27": ; preds = %"31"
unreachable
"31": ; preds = %"8", %"3"
br i1 undef, label %"27", label %"32"
"32": ; preds = %"31"
br label %"33"
"33": ; preds = %"32", %"9"
ret void
}