[Propeller] Do not generate the BB address map for empty functions.

[rahmanl]

Summary

Empty functions (functions with no real code) are irrelevant for propeller optimizations and their addresses sometimes conflict with other functions which obfuscates the analysis.
This simple change skips the BB address map emission for such functions.

[tmsriram]

llvm/test/CodeGen/X86/basic-block-sections-labels-empty-function.ll

12

Curious, How does this pass? There is a ".section .llvm_bb_addr_map" for func() later.

[rahmanl]

llvm/test/CodeGen/X86/basic-block-sections-labels-empty-function.ll

12

Right. I learned it too. FileCheck documentation says 'The “CHECK-NOT:” directive is used to verify that a string doesn’t occur between two matches' So this CHECK-NOT is evaluated against the next CHECK.

[rahmanl]

llvm/test/CodeGen/X86/basic-block-sections-labels-empty-function.ll

12

Sorry. bad link above: https://llvm.org/docs/CommandGuide/FileCheck.html#the-check-not-directive

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

void AsmPrinter::emitFunctionBody() {
   // Emit post-function debug and/or EH information.
   for (const HandlerInfo &HI : Handlers) {
     NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
                        HI.TimerGroupDescription, TimePassesIsEnabled);
     HI.Handler->endFunction(MF);
   }
 
   // Emit section containing BB address offsets and their metadata, when
-  // BB labels are requested for this function.
-  if (MF->hasBBLabels())
+  // BB labels are requested for this function. Skip empty functions.
+  if (MF->hasBBLabels() && HasAnyRealCode)
     emitBBAddrMapSection(*MF);
 
   // Emit section containing stack size metadata.
   emitStackSizeSection(*MF);
 
   emitPatchableFunctionEntries();
 
   if (isVerbose())

llvm/test/CodeGen/X86/basic-block-sections-labels-empty-function.ll

+;; Verify that the BB address map is not emitted for empty functions.
+; RUN: llc < %s -mtriple=x86_64 -basic-block-sections=labels | FileCheck %s
+
+define void @empty_func() {
+entry:
+  unreachable
+}
+; CHECK:    {{^ *}}.text{{$}}
+; CHECK:  empty_func:
+; CHECK:  .Lfunc_begin0:
+; CHECK-NOT:  .section  .llvm_bb_addr_map
+
+define void @func() {
+entry:
+  ret void
+}
+
+; CHECK:  func:
+; CHECK:  .Lfunc_begin1:
+; CHECK:    .section  .llvm_bb_addr_map,"o",@llvm_bb_addr_map,.text{{$}}
+; CHECK:    .quad .Lfunc_begin1