[StandardInstrumentations] Assign names to basic blocks without names

[aeubanks]

Summary

Fixes code in OrderedChangedData<T>::report which assumes that a string will only appear once in Before/After.

[jamieschmeiser]

LGTM.

I'm wondering what would happen (after this change) if a function were to re-order the blocks (without any other change). EG, the first 2 blocks in the function are swapped in the function list of blocks with no other change. I suspect that this would then indicate that the change was the original block 1 was replaced with the new block 2 and the original block 2 was replaced with the new block 1 with the corresponding changes to the branches. I think that may be unavoidable since the comparisons are string based. Besides, it is better than crashing...

Thanks for fixing this.

llvm/lib/Passes/StandardInstrumentations.cpp

template <typename T> void IRComparer<T>::analyzeIR(Any IR, IRDataT<T> &Data) {
   assert(F && "Unknown IR unit.");
   generateFunctionData(Data, *F);
 }
 
 template <typename T>
 bool IRComparer<T>::generateFunctionData(IRDataT<T> &Data, const Function &F) {
   if (!F.isDeclaration() && isFunctionInPrintList(F.getName())) {
     FuncDataT<T> FD(F.getEntryBlock().getName().str());
+    int I = 0;
     for (const auto &B : F) {
-      FD.getOrder().emplace_back(B.getName());
-      FD.getData().insert({B.getName(), B});
+      std::string BBName = B.getName().str();
+      if (BBName.empty()) {
+        BBName = formatv("{0}", I);
+        ++I;
+      }
+      FD.getOrder().emplace_back(BBName);
+      FD.getData().insert({BBName, B});
     }
     Data.getOrder().emplace_back(F.getName());
     Data.getData().insert({F.getName(), FD});
     return true;
   }
   return false;
 }
 

llvm/test/Other/ChangePrinters/print-changed-diff-empty-bb-name.ll

+; RUN: opt -passes=inline %s -disable-output --print-changed=diff 2>&1 | FileCheck %s
+
+; CHECK: IR Dump After InlinerPass
+
+define void @f(i1 %i) {
+  call void @g(i1 %i)
+  ret void
+}
+
+define void @g(i1 %i) {
+  br i1 %i, label %1, label %2
+
+1:
+  ret void
+
+2:
+  ret void
+}