Set the default for -bbsections-cold-text-prefix to .text.split.

[snehasish]

Summary

After using this for a while, we find that it is generally useful to
have it set to .text.split. by default, removing the need for an
additional -mllvm option.

[snehasish]

Updated tests to use .text.split. prefix.

[tmsriram]

This LGTM as there is an option to keep it in ".text.unlikely" if desired. Please wait for Eric's response too. Thanks!

[MaskRay]

Please fix the comment in TargetLoweringObjectFileImpl.cpp:879

[snehasish]

Update comment and rebase.

[MaskRay]

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

870

.text.split -> .text.split.

[snehasish]

Update prefix to .text.split.

[snehasish]

Thanks for the review.

[snehasish]

Rebase.

llvm/lib/CodeGen/BasicBlockSections.cpp

 using llvm::SmallSet;
 using llvm::SmallVector;
 using llvm::StringMap;
 using llvm::StringRef;
 using namespace llvm;
 
 // Placing the cold clusters in a separate section mitigates against poor
 // profiles and allows optimizations such as hugepage mapping to be applied at a
-// section granularity. Where necessary, users should set this to ".text.split."
-// which is recognized by lld via the `-z keep-text-section-prefix` flag.
+// section granularity. Defaults to ".text.split." which is recognized by lld
+// via the `-z keep-text-section-prefix` flag.
 cl::opt<std::string> llvm::BBSectionsColdTextPrefix(
     "bbsections-cold-text-prefix",
     cl::desc("The text prefix to use for cold basic block clusters"),
-    cl::init(".text.unlikely."), cl::Hidden);
+    cl::init(".text.split."), cl::Hidden);
 
 namespace {
 
 // This struct represents the cluster information for a machine basic block.
 struct BBClusterInfo {
   // MachineBasicBlock ID.
   unsigned MBBNumber;
   // Cluster ID this basic block belongs to.

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

 
 /// Returns a unique section for the given machine basic block.
 MCSection *TargetLoweringObjectFileELF::getSectionForMachineBasicBlock(
     const Function &F, const MachineBasicBlock &MBB,
     const TargetMachine &TM) const {
   assert(MBB.isBeginSection() && "Basic block does not start a section!");
   unsigned UniqueID = MCContext::GenericSectionID;
 
-  // For cold sections use the .text.unlikely prefix along with the parent
+  // For cold sections use the .text.split. prefix along with the parent
   // function name. All cold blocks for the same function go to the same
   // section. Similarly all exception blocks are grouped by symbol name
   // under the .text.eh prefix. For regular sections, we either use a unique
   // name, or a unique ID for the section.
   SmallString<128> Name;
   if (MBB.getSectionID() == MBBSectionID::ColdSectionID) {
     Name += BBSectionsColdTextPrefix;
     Name += MBB.getParent()->getName();

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

 ; LINUX-SECTIONS1-LABEL:  foo:
 ; LINUX-SECTIONS1:    jne foo.1
 ; LINUX-SECTIONS1-NOT:    {{jne|je|jmp}}
 ; LINUX-SECTIONS1-LABEL:  # %bb.2:
 ; LINUX-SECTIONS1:    jmp foo.cold
 ; LINUX-SECTIONS1:    .section        .text.foo,"ax",@progbits,unique,1
 ; LINUX-SECTIONS1-LABEL:  foo.1:
 ; LINUX-SECTIONS1:    jmp foo.cold
-; LINUX-SECTIONS1:    .section        .text.unlikely.foo,"ax",@progbits
+; LINUX-SECTIONS1:    .section        .text.split.foo,"ax",@progbits
 ; LINUX-SECTIONS1-LABEL:  foo.cold:
 
 ; LINUX-SECTIONS2:    .section        .text.foo,"ax",@progbits
 ; LINUX-SECTIONS2-LABEL:  foo:
 ; LINUX-SECTIONS2:    jne foo.0
 ; LINUX-SECTIONS2-NOT:    {{jne|je|jmp}}
 ; LINUX-SECTIONS2-LABEL:  # %bb.2:
 ; LINUX-SECTIONS2:    jmp .LBB0_3
 ; LINUX-SECTIONS2:    .section        .text.foo,"ax",@progbits,unique,1
 ; LINUX-SECTIONS2:    foo.0:
 ; LINUX-SECTIONS2-NOT:    {{jne|je|jmp}}
 ; LINUX-SECTIONS2:    .LBB0_3:

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

 ; LINUX-SECTIONS1-NOT:    .LBB_END0_{{0-9}}+
 ; LINUX-SECTIONS1-LABEL:  # %bb.2:
 ; LINUX-SECTIONS1-NOT:    .LBB_END0_{{0-9}}+
 ; LINUX-SECTIONS1:    .section        .text.foo,"ax",@progbits,unique,1
 ; LINUX-SECTIONS1-LABEL:  foo.1:
 ; LINUX-SECTIONS1-LABEL:  .LBB_END0_1:
 ; LINUX-SECTIONS1-NEXT:        .size   foo.1, .LBB_END0_1-foo.1
 ; LINUX-SECTIONS1-NOT:    .section
-; LINUX-SECTIONS1:    .section        .text.unlikely.foo,"ax",@progbits
+; LINUX-SECTIONS1:    .section        .text.split.foo,"ax",@progbits
 ; LINUX-SECTIONS1-LABEL:  foo.cold:
 ; LINUX-SECTIONS1-LABEL:  .LBB_END0_3:
 ; LINUX-SECTIONS1-NEXT:        .size   foo.cold, .LBB_END0_3-foo.cold
 ; LINUX-SECTIONS1:      .section  .text.foo,"ax",@progbits
 ; LINUX-SECTIONS1-LABEL:  .Lfunc_end0:
 ; LINUX-SECTIONS1-NEXT:   .size foo, .Lfunc_end0-foo
 
 ; LINUX-SECTIONS2:    .section        .text.foo,"ax",@progbits

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

 ; Check if basic blocks that don't get unique sections are placed in cold sections.
 ; Basic block with id 1 and 2 must be in the cold section.
 ; RUN: echo '!_Z3bazb' > %t
 ; RUN: echo '!!0' >> %t
 ; RUN: llc < %s -mtriple=x86_64 -function-sections -basic-block-sections=%t -unique-basic-block-section-names | FileCheck %s -check-prefix=LINUX-SECTIONS
-; RUN: llc < %s -mtriple=x86_64 -function-sections -basic-block-sections=%t -unique-basic-block-section-names -bbsections-cold-text-prefix=".text.split." | FileCheck %s -check-prefix=LINUX-SPLIT
+; RUN: llc < %s -mtriple=x86_64 -function-sections -basic-block-sections=%t -unique-basic-block-section-names -bbsections-cold-text-prefix=".text.unlikely." | FileCheck %s -check-prefix=LINUX-SPLIT
 
 define void @_Z3bazb(i1 zeroext %0) nounwind {
   br i1 %0, label %2, label %4
 
 2:                                                ; preds = %1
   %3 = call i32 @_Z3barv()
   br label %6
 

 
 declare i32 @_Z3foov() #1
 
 ; LINUX-SECTIONS: .section        .text._Z3bazb,"ax",@progbits
 ; LINUX-SECTIONS: _Z3bazb:
 ; Check that the basic block with id 1 doesn't get a section.
 ; LINUX-SECTIONS-NOT: .section        .text._Z3bazb._Z3bazb.1,"ax",@progbits,unique
 ; Check that a single cold section is started here and id 1 and 2 blocks are placed here.
-; LINUX-SECTIONS: .section  .text.unlikely._Z3bazb,"ax",@progbits
+; LINUX-SECTIONS: .section  .text.split._Z3bazb,"ax",@progbits
 ; LINUX-SECTIONS: _Z3bazb.cold:
 ; LINUX-SECTIONS-NOT: .section        .text._Z3bazb._Z3bazb.2,"ax",@progbits,unique
 ; LINUX-SECTIONS: .LBB0_2:
 ; LINUX-SECTIONS: .size   _Z3bazb, .Lfunc_end{{[0-9]}}-_Z3bazb
 
-; LINUX-SPLIT:      .section  .text.split._Z3bazb,"ax",@progbits
+; LINUX-SPLIT:      .section  .text.unlikely._Z3bazb,"ax",@progbits
 ; LINUX-SPLIT-NEXT: _Z3bazb.cold:
 ; LINUX-SPLIT-NEXT:   callq _Z3barv
 ; LINUX-SPLIT:      .LBB0_2:
 ; LINUX-SPLIT:      .LBB_END0_2:

llvm/test/CodeGen/X86/machine-function-splitter.ll

 ; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -split-machine-functions | FileCheck %s -check-prefix=MFS-DEFAULTS
 ; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -split-machine-functions -mfs-count-threshold=2000 | FileCheck %s --dump-input=always -check-prefix=MFS-OPTS1
 ; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -split-machine-functions -mfs-psi-cutoff=950000 | FileCheck %s -check-prefix=MFS-OPTS2
 
 define void @foo1(i1 zeroext %0) nounwind !prof !14 !section_prefix !15 {
-;; Check that cold block is moved to .text.unlikely.
+;; Check that cold block is moved to .text.split.
 ; MFS-DEFAULTS-LABEL: foo1
-; MFS-DEFAULTS:       .section        .text.unlikely.foo1
+; MFS-DEFAULTS:       .section        .text.split.foo1
 ; MFS-DEFAULTS-NEXT:  foo1.cold:
 ; MFS-DEFAULTS-NOT:   callq   bar
 ; MFS-DEFAULTS-NEXT:  callq   baz
   br i1 %0, label %2, label %4, !prof !17
 
 2:                                                ; preds = %1
   %3 = call i32 @bar()
   br label %6

 6:                                                ; preds = %4, %2
   %7 = tail call i32 @qux()
   ret void
 }
 
 define void @foo4(i1 zeroext %0, i1 zeroext %1) nounwind !prof !20 {
 ;; Check that count threshold works.
 ; MFS-OPTS1-LABEL: foo4
-; MFS-OPTS1:       .section        .text.unlikely.foo4
+; MFS-OPTS1:       .section        .text.split.foo4
 ; MFS-OPTS1-NEXT:  foo4.cold:
 ; MFS-OPTS1-NOT:   callq    bar
 ; MFS-OPTS1-NOT:   callq    baz
 ; MFS-OPTS1-NEXT:  callq    bam
   br i1 %0, label %3, label %7, !prof !18
 
 3:
   %4 = call i32 @bar()

 12:
   %13 = tail call i32 @qux()
   ret void
 }
 
 define void @foo5(i1 zeroext %0, i1 zeroext %1) nounwind !prof !20 {
 ;; Check that profile summary info cutoff works.
 ; MFS-OPTS2-LABEL: foo5
-; MFS-OPTS2:       .section        .text.unlikely.foo5
+; MFS-OPTS2:       .section        .text.split.foo5
 ; MFS-OPTS2-NEXT:       foo5.cold:
 ; MFS-OPTS2-NOT:   callq    bar
 ; MFS-OPTS2-NOT:   callq    baz
 ; MFS-OPTS2-NEXT:  callq    bam
   br i1 %0, label %3, label %7, !prof !21
 
 3:
   %4 = call i32 @bar()

 6:                                                ; preds = %4, %2
   %7 = tail call i32 @qux()
   ret void
 }
 
 define i32 @foo7(i1 zeroext %0) personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) !prof !14 {
 ;; Check that cold ehpads are not split out.
 ; MFS-DEFAULTS-LABEL: foo7
-; MFS-DEFAULTS:       .section        .text.unlikely.foo7,"ax",@progbits
+; MFS-DEFAULTS:       .section        .text.split.foo7,"ax",@progbits
 ; MFS-DEFAULTS-NEXT:  foo7.cold:
 ; MFS-DEFAULTS-NOT:   callq   _Unwind_Resume
 ; MFS-DEFAULTS:       callq   baz
 entry:
   invoke void @_Z1fv()
           to label %try.cont unwind label %lpad
 
 lpad: