[Dominators] Make RemoveUnreachableBlocks return false if the BasicBlock is already awaiting deletion
Summary:
Previously, `removeUnreachableBlocks` still returns true (which indicates the CFG is changed) even when all the unreachable blocks found is awaiting deletion in the DDT class.
This makes code pattern like
```
// Code modified from lib/Transforms/Scalar/SimplifyCFGPass.cpp
bool EverChanged = removeUnreachableBlocks(F, nullptr, DDT);
...
do {
EverChanged = someMightHappenModifications();
EverChanged |= removeUnreachableBlocks(F, nullptr, DDT);
} while (EverChanged);
```
become a dead loop.
Fix this by detecting whether a BasicBlock is already awaiting deletion.
Reviewers: kuhar, brzycki, dmgreen, grosser, davide
Reviewed By: kuhar, brzycki
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D49738
llvm-svn: 338882
diff --git a/llvm/unittests/Transforms/Utils/Local.cpp b/llvm/unittests/Transforms/Utils/Local.cpp
index 312c32e..53cfc6b 100644
--- a/llvm/unittests/Transforms/Utils/Local.cpp
+++ b/llvm/unittests/Transforms/Utils/Local.cpp
@@ -844,4 +844,23 @@
runWithDomTree(*M, "br_self_loop", runLazy);
runWithDomTree(*M, "br_constant", runLazy);
runWithDomTree(*M, "br_loop", runLazy);
+
+ M = parseIR(C,
+ R"(
+ define void @f() {
+ entry:
+ ret void
+ bb0:
+ ret void
+ }
+ )");
+
+ auto checkRUBlocksRetVal = [&](Function &F, DominatorTree *DT) {
+ DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
+ EXPECT_TRUE(removeUnreachableBlocks(F, nullptr, &DTU));
+ EXPECT_FALSE(removeUnreachableBlocks(F, nullptr, &DTU));
+ EXPECT_TRUE(DTU.getDomTree().verify());
+ };
+
+ runWithDomTree(*M, "f", checkRUBlocksRetVal);
}
\ No newline at end of file