[PATCH] D38960: [Local] Fix a bug in the domtree update logic for MergeBasicBlockIntoOnlyPred.

[Balaram Makam via Phabricator via llvm-commits]

bmakam updated this revision to Diff 119347.
bmakam added a comment.

Reduce unittest.


https://reviews.llvm.org/D38960

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
@@ -166,3 +166,48 @@
       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());
+      });
+}
Index: lib/Transforms/Utils/Local.cpp
===================================================================
--- lib/Transforms/Utils/Local.cpp
+++ lib/Transforms/Utils/Local.cpp
@@ -621,9 +621,13 @@
     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();


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