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[Local] Fix a bug in the domtree update logic for MergeBasicBlockIntoOnlyPred. 

Summary: For some irreducible CFG the domtree nodes might be dead, do not update domtree for dead nodes.

Reviewers: kuhar, dberlin, hfinkel

Reviewed By: kuhar

Subscribers: llvm-commits, mcrosier

Differential Revision: https://reviews.llvm.org/D38960

llvm-svn: 316582
This commit is contained in:
Balaram Makam 2017-10-25 14:55:48 +00:00
parent 3e94e441d6
commit 925ddf1a93
2 changed files with 52 additions and 3 deletions
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10
llvm/lib/Transforms/Utils/Local.cpp
View File

@ -649,9 +649,13 @@ void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, DominatorTree *DT) {
DestBB->moveAfter(PredBB);
if (DT) {
BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock();
DT->changeImmediateDominator(DestBB, PredBBIDom);
DT->eraseNode(PredBB);
// For some irreducible CFG we end up having forward-unreachable blocks
// so check if getNode returns a valid node before updating the domtree.
if (DomTreeNode *DTN = DT->getNode(PredBB)) {
BasicBlock *PredBBIDom = DTN->getIDom()->getBlock();
DT->changeImmediateDominator(DestBB, PredBBIDom);
DT->eraseNode(PredBB);
}
}
// Nuke BB.
PredBB->eraseFromParent();

45
llvm/unittests/Transforms/Utils/Local.cpp
View File

@ -166,3 +166,48 @@ TEST(Local, ReplaceDbgDeclare) {
Declares++;
EXPECT_EQ(2, Declares);
}
/// Build the dominator tree for the function and run the Test.
static void runWithDomTree(
Module &M, StringRef FuncName,
function_ref<void(Function &F, DominatorTree *DT)> Test) {
auto *F = M.getFunction(FuncName);
ASSERT_NE(F, nullptr) << "Could not find " << FuncName;
// Compute the dominator tree for the function.
DominatorTree DT(*F);
Test(*F, &DT);
}
TEST(Local, MergeBasicBlockIntoOnlyPred) {
LLVMContext C;
std::unique_ptr<Module> M = parseIR(
C,
"define i32 @f(i8* %str) {\n"
"entry:\n"
" br label %bb2.i\n"
"bb2.i: ; preds = %bb4.i, %entry\n"
" br i1 false, label %bb4.i, label %base2flt.exit204\n"
"bb4.i: ; preds = %bb2.i\n"
" br i1 false, label %base2flt.exit204, label %bb2.i\n"
"bb10.i196.bb7.i197_crit_edge: ; No predecessors!\n"
" br label %bb7.i197\n"
"bb7.i197: ; preds = %bb10.i196.bb7.i197_crit_edge\n"
" %.reg2mem.0 = phi i32 [ %.reg2mem.0, %bb10.i196.bb7.i197_crit_edge ]\n"
" br i1 undef, label %base2flt.exit204, label %base2flt.exit204\n"
"base2flt.exit204: ; preds = %bb7.i197, %bb7.i197, %bb2.i, %bb4.i\n"
" ret i32 0\n"
"}\n");
runWithDomTree(
*M, "f", [&](Function &F, DominatorTree *DT) {
for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
BasicBlock *BB = &*I++;
BasicBlock *SinglePred = BB->getSinglePredecessor();
if (!SinglePred || SinglePred == BB || BB->hasAddressTaken()) continue;
BranchInst *Term = dyn_cast<BranchInst>(SinglePred->getTerminator());
if (Term && !Term->isConditional())
MergeBasicBlockIntoOnlyPred(BB, DT);
}
EXPECT_TRUE(DT->verify());
});
}