[PATCH] D60082: Not all blocks are reachable from entry. Don't assume they are.

[Nick Lewycky via Phabricator via llvm-commits]

nicholas created this revision.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

Fixes a bug in isPotentiallyReachable, noticed by inspection.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D60082

Files:
  llvm/lib/Analysis/CFG.cpp
  llvm/unittests/Analysis/CFGTest.cpp


Index: llvm/unittests/Analysis/CFGTest.cpp
===================================================================
--- llvm/unittests/Analysis/CFGTest.cpp
+++ llvm/unittests/Analysis/CFGTest.cpp
@@ -385,3 +385,43 @@
   S[0] = OldBB;
   ExpectPath(true);
 }
+
+TEST_F(IsPotentiallyReachableTest, UnreachableFromEntryTest) {
+  ParseAssembly("define void @test() {\n"
+                "entry:\n"
+                "  %A = bitcast i8 undef to i8\n"
+                "  ret void\n"
+                "not.reachable:\n"
+                "  %B = bitcast i8 undef to i8\n"
+                "  ret void\n"
+                "}");
+  ExpectPath(false);
+}
+
+TEST_F(IsPotentiallyReachableTest, UnreachableBlocksTest1) {
+  ParseAssembly("define void @test() {\n"
+                "entry:\n"
+                "  ret void\n"
+                "not.reachable.1:\n"
+                "  %A = bitcast i8 undef to i8\n"
+                "  br label %not.reachable.2\n"
+                "not.reachable.2:\n"
+                "  %B = bitcast i8 undef to i8\n"
+                "  ret void\n"
+                "}");
+  ExpectPath(true);
+}
+
+TEST_F(IsPotentiallyReachableTest, UnreachableBlocksTest2) {
+  ParseAssembly("define void @test() {\n"
+                "entry:\n"
+                "  ret void\n"
+                "not.reachable.1:\n"
+                "  %B = bitcast i8 undef to i8\n"
+                "  br label %not.reachable.2\n"
+                "not.reachable.2:\n"
+                "  %A = bitcast i8 undef to i8\n"
+                "  ret void\n"
+                "}");
+  ExpectPath(false);
+}
Index: llvm/lib/Analysis/CFG.cpp
===================================================================
--- llvm/lib/Analysis/CFG.cpp
+++ llvm/lib/Analysis/CFG.cpp
@@ -226,10 +226,17 @@
     Worklist.push_back(const_cast<BasicBlock*>(A->getParent()));
   }
 
-  if (A->getParent() == &A->getParent()->getParent()->getEntryBlock())
-    return true;
-  if (B->getParent() == &A->getParent()->getParent()->getEntryBlock())
-    return false;
+  if (DT) {
+    if (DT->isReachableFromEntry(A->getParent()) !=
+        DT->isReachableFromEntry(B->getParent()))
+      return false;
+    if (A->getParent() == &A->getParent()->getParent()->getEntryBlock() &&
+        DT->isReachableFromEntry(B->getParent()))
+      return true;
+    if (B->getParent() == &A->getParent()->getParent()->getEntryBlock() &&
+        DT->isReachableFromEntry(A->getParent()))
+      return false;
+  }
 
   return isPotentiallyReachableFromMany(
       Worklist, const_cast<BasicBlock *>(B->getParent()), DT, LI);


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