[CodeGen] Basic block sections should take precedence over splitting.

[snehasish]

Summary

The use of basic block sections should take precedence over the machine
function splitting pass. Since they use the same underlying mechanism
they are kept exclusive. Updated the tests to check that split machine
functions is overridden by all flavours of basic block sections.

[tmsriram]

llvm/lib/CodeGen/TargetPassConfig.cpp

1190–1193

Could you add a TODO here that Machine Function Splitting and Basic Block Labels are in principle fine together but we have not addressed it yet?

[snehasish]

Added FIXME to clarify that Labels and splitting can be enabled together but we don't support it yet.

llvm/lib/CodeGen/TargetPassConfig.cpp

bool RunOnAllFunctions =
         (EnableMachineOutliner == RunOutliner::AlwaysOutline);
     bool AddOutliner =
         RunOnAllFunctions || TM->Options.SupportsDefaultOutlining;
     if (AddOutliner)
       addPass(createMachineOutlinerPass(RunOnAllFunctions));
   }
 
   // Machine function splitter uses the basic block sections feature. Both
-  // cannot be enabled at the same time.
-  if (TM->Options.EnableMachineFunctionSplitter ||
+  // cannot be enabled at the same time. Basic block sections takes precedence.
+  // FIXME: In principle, BasicBlockSection::Labels and splitting can used
+  // together. Update this check once we have addressed any issues.
+  if (TM->getBBSectionsType() != llvm::BasicBlockSection::None) {
+    addPass(llvm::createBasicBlockSectionsPass(TM->getBBSectionsFuncListBuf()));
+  } else if (TM->Options.EnableMachineFunctionSplitter ||
              EnableMachineFunctionSplitter) {
     addPass(createMachineFunctionSplitterPass());
-  } else if (TM->getBBSectionsType() != llvm::BasicBlockSection::None) {
-    addPass(llvm::createBasicBlockSectionsPass(TM->getBBSectionsFuncListBuf()));
   }
 
   // Add passes that directly emit MI after all other MI passes.
   addPreEmitPass2();
 
   // Insert pseudo probe annotation for callsite profiling
   if (TM->Options.PseudoProbeForProfiling)
     addPass(createPseudoProbeInserter());

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

 ; Check the basic block sections labels option
 ; RUN: llc < %s -mtriple=x86_64 -function-sections -unique-section-names=true -basic-block-sections=labels | FileCheck %s --check-prefix=UNIQ
 ; RUN: llc < %s -mtriple=x86_64 -function-sections -unique-section-names=false -basic-block-sections=labels | FileCheck %s --check-prefix=NOUNIQ
+; RUN: llc < %s -mtriple=x86_64 -function-sections -unique-section-names=true -basic-block-sections=labels -split-machine-functions | FileCheck %s --check-prefix=UNIQ
 
 define void @_Z3bazb(i1 zeroext) personality i32 (...)* @__gxx_personality_v0 {
   br i1 %0, label %2, label %7
 
 2:
   %3 = invoke i32 @_Z3barv()
           to label %7 unwind label %5
   br label %9

llvm/test/CodeGen/X86/basic-block-sections-list.ll

 ; Check the basic block sections list option.
 ; RUN: echo '!_Z3foob' > %t
 ; RUN: llc < %s -mtriple=x86_64-pc-linux -function-sections -basic-block-sections=%t -unique-basic-block-section-names | FileCheck %s -check-prefix=LINUX-SECTIONS
+; RUN: llc < %s -mtriple=x86_64-pc-linux -function-sections -basic-block-sections=%t -unique-basic-block-section-names -split-machine-functions | FileCheck %s -check-prefix=LINUX-SECTIONS
 
 define i32 @_Z3foob(i1 zeroext %0) nounwind {
   %2 = alloca i32, align 4
   %3 = alloca i8, align 1
   %4 = zext i1 %0 to i8
   store i8 %4, i8* %3, align 1
   %5 = load i8, i8* %3, align 1
   %6 = trunc i8 %5 to i1

llvm/test/CodeGen/X86/basic-block-sections.ll

 ; RUN: llc < %s -mtriple=x86_64-pc-linux -function-sections -basic-block-sections=all -unique-basic-block-section-names | FileCheck %s -check-prefix=LINUX-SECTIONS
 ; RUN: llc < %s -mtriple=i386-unknown-linux-gnu  -function-sections -basic-block-sections=all -unique-basic-block-section-names | FileCheck %s -check-prefix=LINUX-SECTIONS
+; RUN: llc < %s -mtriple=x86_64-pc-linux -function-sections -basic-block-sections=all -unique-basic-block-section-names -split-machine-functions | FileCheck %s -check-prefix=LINUX-SECTIONS
 
 define void @_Z3bazb(i1 zeroext) nounwind {
   %2 = alloca i8, align 1
   %3 = zext i1 %0 to i8
   store i8 %3, i8* %2, align 1
   %4 = load i8, i8* %2, align 1
   %5 = trunc i8 %4 to i1
   br i1 %5, label %6, label %8