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[Dominators] Fix some edge cases for PostDomTree updating 

These fix some odd cfg cases where batch-updating the post
dom tree fails. Usually around infinite loops and roots
ending up being different.

Differential Revision: https://reviews.llvm.org/D42247

llvm-svn: 323034
This commit is contained in:
David Green 2018-01-20 10:29:37 +00:00
parent 81ac12d1b4
commit 990eb1fc94
2 changed files with 109 additions and 14 deletions
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28
llvm/include/llvm/Support/GenericDomTreeConstruction.h
View File

@ -706,7 +706,7 @@ struct SemiNCAInfo {
// algorithm does not really know or use the set of roots and can make a
// different (implicit) decision about which nodes within an infinite loop
// becomes a root.
if (DT.isVirtualRoot(TN->getIDom())) {
if (TN && !DT.isVirtualRoot(TN->getIDom())) {
DEBUG(dbgs() << "Root " << BlockNamePrinter(R)
<< " is not virtual root's child\n"
<< "The entire tree needs to be rebuilt\n");
@ -940,21 +940,21 @@ struct SemiNCAInfo {
const NodePtr NCDBlock = DT.findNearestCommonDominator(From, To);
const TreeNodePtr NCD = DT.getNode(NCDBlock);
// To dominates From -- nothing to do.
if (ToTN == NCD) return;
// If To dominates From -- nothing to do.
if (ToTN != NCD) {
DT.DFSInfoValid = false;
DT.DFSInfoValid = false;
const TreeNodePtr ToIDom = ToTN->getIDom();
DEBUG(dbgs() << "\tNCD " << BlockNamePrinter(NCD) << ", ToIDom "
<< BlockNamePrinter(ToIDom) << "\n");
const TreeNodePtr ToIDom = ToTN->getIDom();
DEBUG(dbgs() << "\tNCD " << BlockNamePrinter(NCD) << ", ToIDom "
<< BlockNamePrinter(ToIDom) << "\n");
// To remains reachable after deletion.
// (Based on the caption under Figure 4. from the second paper.)
if (FromTN != ToIDom || HasProperSupport(DT, BUI, ToTN))
DeleteReachable(DT, BUI, FromTN, ToTN);
else
DeleteUnreachable(DT, BUI, ToTN);
// To remains reachable after deletion.
// (Based on the caption under Figure 4. from the second paper.)
if (FromTN != ToIDom || HasProperSupport(DT, BUI, ToTN))
DeleteReachable(DT, BUI, FromTN, ToTN);
else
DeleteUnreachable(DT, BUI, ToTN);
}
if (IsPostDom) UpdateRootsAfterUpdate(DT, BUI);
}

95
llvm/unittests/IR/DominatorTreeBatchUpdatesTest.cpp
View File

@ -258,3 +258,98 @@ TEST(DominatorTreeBatchUpdates, InsertDeleteExhaustive) {
EXPECT_TRUE(PDT.verify());
}
}
// These are some odd flowgraphs, usually generated from csmith cases,
// which are difficult on post dom trees.
TEST(DominatorTreeBatchUpdates, InfiniteLoop) {
std::vector<CFGBuilder::Arc> Arcs = {
{"1", "2"},
{"2", "3"},
{"3", "6"}, {"3", "5"},
{"4", "5"},
{"5", "2"},
{"6", "3"}, {"6", "4"}};
// SplitBlock on 3 -> 5
std::vector<CFGBuilder::Update> Updates = {
{CFGInsert, {"N", "5"}}, {CFGInsert, {"3", "N"}}, {CFGDelete, {"3", "5"}}};
CFGHolder Holder;
CFGBuilder B(Holder.F, Arcs, Updates);
DominatorTree DT(*Holder.F);
EXPECT_TRUE(DT.verify());
PostDomTree PDT(*Holder.F);
EXPECT_TRUE(PDT.verify());
while (B.applyUpdate())
;
auto DomUpdates = ToDomUpdates(B, Updates);
DT.applyUpdates(DomUpdates);
EXPECT_TRUE(DT.verify());
PDT.applyUpdates(DomUpdates);
EXPECT_TRUE(PDT.verify());
}
TEST(DominatorTreeBatchUpdates, DeadBlocks) {
std::vector<CFGBuilder::Arc> Arcs = {
{"1", "2"},
{"2", "3"},
{"3", "4"}, {"3", "7"},
{"4", "4"},
{"5", "6"}, {"5", "7"},
{"6", "7"},
{"7", "2"}, {"7", "8"}};
// Remove dead 5 and 7,
// plus SplitBlock on 7 -> 8
std::vector<CFGBuilder::Update> Updates = {
{CFGDelete, {"6", "7"}}, {CFGDelete, {"5", "7"}}, {CFGDelete, {"5", "6"}},
{CFGInsert, {"N", "8"}}, {CFGInsert, {"7", "N"}}, {CFGDelete, {"7", "8"}}};
CFGHolder Holder;
CFGBuilder B(Holder.F, Arcs, Updates);
DominatorTree DT(*Holder.F);
EXPECT_TRUE(DT.verify());
PostDomTree PDT(*Holder.F);
EXPECT_TRUE(PDT.verify());
while (B.applyUpdate())
;
auto DomUpdates = ToDomUpdates(B, Updates);
DT.applyUpdates(DomUpdates);
EXPECT_TRUE(DT.verify());
PDT.applyUpdates(DomUpdates);
EXPECT_TRUE(PDT.verify());
}
TEST(DominatorTreeBatchUpdates, InfiniteLoop2) {
std::vector<CFGBuilder::Arc> Arcs = {
{"1", "2"},
{"2", "6"}, {"2", "3"},
{"3", "4"},
{"4", "5"}, {"4", "6"},
{"5", "4"},
{"6", "2"}};
// SplitBlock on 4 -> 6
std::vector<CFGBuilder::Update> Updates = {
{CFGInsert, {"N", "6"}}, {CFGInsert, {"4", "N"}}, {CFGDelete, {"4", "6"}}};
CFGHolder Holder;
CFGBuilder B(Holder.F, Arcs, Updates);
DominatorTree DT(*Holder.F);
EXPECT_TRUE(DT.verify());
PostDomTree PDT(*Holder.F);
EXPECT_TRUE(PDT.verify());
while (B.applyUpdate())
;
auto DomUpdates = ToDomUpdates(B, Updates);
DT.applyUpdates(DomUpdates);
EXPECT_TRUE(DT.verify());
PDT.applyUpdates(DomUpdates);
EXPECT_TRUE(PDT.verify());
}