[BasicBlockUtils] Add BasicBlock printer (#163066)

Author: ro-i

llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h

@@ -612,6 +612,8 @@ LLVM_ABI void InvertBranch(BranchInst *PBI, IRBuilderBase &Builder);
 // br/brcond/unreachable/ret
 LLVM_ABI bool hasOnlySimpleTerminator(const Function &F);
 
+/// Print BasicBlock \p BB as an operand or print "<nullptr>" if \p BB is a
+/// nullptr.
 LLVM_ABI Printable printBasicBlock(const BasicBlock *BB);
 
 } // end namespace llvm

llvm/lib/Transforms/Utils/BasicBlockUtils.cpp

@@ -1778,7 +1778,10 @@ bool llvm::hasOnlySimpleTerminator(const Function &F) {
 
 Printable llvm::printBasicBlock(const BasicBlock *BB) {
   return Printable([BB](raw_ostream &OS) {
-    if (BB)
-      return BB->printAsOperand(OS);
+    if (!BB) {
+      OS << "<nullptr>";
+      return;
+    }
+    BB->printAsOperand(OS);
   });
 }

llvm/unittests/Transforms/Utils/BasicBlockUtilsTest.cpp

@@ -716,3 +716,32 @@ attributes #0 = { presplitcoroutine }
   EXPECT_FALSE(llvm::isPresplitCoroSuspendExitEdge(
       *ExitN.getSinglePredecessor(), ExitN));
 }
+
+TEST(BasicBlockUtils, BasicBlockPrintable) {
+  std::string S;
+  std::string SCheck;
+  llvm::raw_string_ostream OS{S};
+  llvm::raw_string_ostream OSCheck{SCheck};
+
+  LLVMContext C;
+  std::unique_ptr<Module> M = parseIR(C, R"IR(
+define void @foo() {
+  br label %bb0
+bb0:
+  br label %.exit
+.exit:
+  ret void
+}
+)IR");
+
+  Function *F = M->getFunction("foo");
+  for (const BasicBlock &BB : *F) {
+    OS << printBasicBlock(&BB);
+    BB.printAsOperand(OSCheck);
+    EXPECT_EQ(OS.str(), OSCheck.str());
+    S.clear();
+    SCheck.clear();
+  }
+  OS << printBasicBlock(nullptr);
+  EXPECT_EQ(OS.str(), "<nullptr>");
+}