[AsmWriter] Construct SlotTracker with the function

This patch teaches BasicBlock::print to construct an instance of
SlotTracker with the containing function.

Without this patch, we dump:

*** IR Dump After LoopInstSimplifyPass ***
; Preheader:
  br label %1

; Loop:
<badref>:                                         ; preds = %1, %0
  br label %1

Note "<badref>" above.  This happens because BasicBlock::print calls:

  SlotTracker SlotTable(this->getModule());

Note that this constructor does not add the contents of functions to
the slot table.  That is, basic blocks are left unnumbered.

This patch fixes the problem by switching to:

  SlotTracker SlotTable(this->getParent());

which does add the contents of the Module and the function,
this->getParent(), to the slot table.

Differential Revision: https://reviews.llvm.org/D89567

Author: kazutakahirata

llvm/lib/IR/AsmWriter.cpp

@@ -4417,7 +4417,7 @@ void Function::print(raw_ostream &ROS, AssemblyAnnotationWriter *AAW,
 void BasicBlock::print(raw_ostream &ROS, AssemblyAnnotationWriter *AAW,
                      bool ShouldPreserveUseListOrder,
                      bool IsForDebug) const {
-  SlotTracker SlotTable(this->getModule());
+  SlotTracker SlotTable(this->getParent());
   formatted_raw_ostream OS(ROS);
   AssemblyWriter W(OS, SlotTable, this->getModule(), AAW,
                    IsForDebug,

llvm/test/Other/bb-badref.ll

@@ -0,0 +1,14 @@
+; RUN: opt -passes=loop-instsimplify -print-after-all -disable-output -S < %s 2>&1 | FileCheck %s
+
+; loop-instsimplify dumps individual basic blocks as part of a loop,
+; not a function.  Verify that the non-entry basic block is labeled as
+; "1", not "<badref>".
+
+; CHECK-NOT: <badref>
+
+define void @foo() {
+  br label %1
+
+1:
+  br label %1
+}