[PATCH] D48256: Fix bug to merge away entry block and update DT correctly.
Xin Tong via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Sat Jun 16 13:07:45 PDT 2018
trentxintong created this revision.
trentxintong added reviewers: davide, mzolotukhin, dberlin.
Fix bug to merge away entry block and update DT correctly.
Repository:
rL LLVM
https://reviews.llvm.org/D48256
Files:
lib/Transforms/Utils/Local.cpp
unittests/Transforms/Utils/Local.cpp
Index: unittests/Transforms/Utils/Local.cpp
===================================================================
--- unittests/Transforms/Utils/Local.cpp
+++ unittests/Transforms/Utils/Local.cpp
@@ -206,6 +206,33 @@
}
EXPECT_TRUE(DT->verify());
});
+
+ // Test we can merge away entry block and update DT correctly.
+ // entry block does not have IDom.
+ std::unique_ptr<Module> M2 = parseIR(C,
+ R"(
+ define i32 @f(i8* %str) {
+ entry:
+ br label %bb2.i
+ bb2.i: ; preds = %bb4.i, %entry
+ br label %base2flt.exit204
+ base2flt.exit204: ; preds = %bb7.i197, %bb7.i197, %bb2.i, %bb4.i
+ ret i32 0
+ }
+ )");
+ runWithDomTree(
+ *M2, "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());
+ });
+
}
TEST(Local, ConstantFoldTerminator) {
Index: lib/Transforms/Utils/Local.cpp
===================================================================
--- lib/Transforms/Utils/Local.cpp
+++ lib/Transforms/Utils/Local.cpp
@@ -714,7 +714,8 @@
if (ReplaceEntryBB)
DestBB->moveAfter(PredBB);
- if (DT) {
+ // Entry block does not have IDom.
+ if (DT && !ReplaceEntryBB) {
// 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)) {
@@ -735,6 +736,11 @@
DDT->applyUpdates(Updates);
} else {
PredBB->eraseFromParent(); // Nuke BB.
+ // The entry block was removed and there is no external interface for the
+ // dominator tree to be notified of this change. In this corner-case we
+ // recalculate the entire tree.
+ if (DT && ReplaceEntryBB)
+ DT->recalculate(*(DestBB->getParent()));
}
}
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