Reapply [ELF] Making cdsort default for function reordering (#68638)

Edited lld/ELF/Options.td to cdsort as well

CDSort function reordering outperforms the existing default heuristic (
hfsort/C^3) in terms of the performance of generated binaries while
being (almost) as fast. Thus, the suggestion is to change the default.
The speedup is up to 1.5% perf for large front-end binaries, and can be
moderate/neutral for "small" benchmarks.

High-level **perf impact** on two selected binaries:
clang-10 binary (built with LTO+AutoFDO/CSSPGO): wins on top of C^3 in
[0.3%..0.8%]
rocksDB-8 binary (built with LTO+CSSPGO): wins on top of C^3 in
[0.8%..1.5%]

More detailed measurements on the clang binary is at
[here](https://reviews.llvm.org/D152834#4445042)

Author: spupyrev

lld/ELF/Driver.cpp

@@ -1095,7 +1095,7 @@ static void ltoValidateAllVtablesHaveTypeInfos(opt::InputArgList &args) {
 }
 
 static CGProfileSortKind getCGProfileSortKind(opt::InputArgList &args) {
-  StringRef s = args.getLastArgValue(OPT_call_graph_profile_sort, "hfsort");
+  StringRef s = args.getLastArgValue(OPT_call_graph_profile_sort, "cdsort");
   if (s == "hfsort")
     return CGProfileSortKind::Hfsort;
   if (s == "cdsort")

lld/ELF/Options.td

@@ -129,9 +129,9 @@ defm call_graph_ordering_file:
   Eq<"call-graph-ordering-file", "Layout sections to optimize the given callgraph">;
 
 def call_graph_profile_sort: JJ<"call-graph-profile-sort=">,
-  HelpText<"Reorder input sections with call graph profile using the specified algorithm (default: hfsort)">,
-  MetaVarName<"[none,hfsort]">,
-  Values<"none,hfsort">;
+  HelpText<"Reorder input sections with call graph profile using the specified algorithm (default: cdsort)">,
+  MetaVarName<"[none,hfsort,cdsort]">,
+  Values<"none,hfsort,cdsort">;
 def : FF<"no-call-graph-profile-sort">, Alias<call_graph_profile_sort>, AliasArgs<["none"]>,
   Flags<[HelpHidden]>;
 

lld/docs/ld.lld.1

@@ -128,9 +128,9 @@ may be:
 .It Cm none
 Ignore call graph profile.
 .It Cm hfsort
-Use hfsort (default).
+Use hfsort.
 .It Cm cdsort
-Use cdsort.
+Use cdsort (default).
 .El
 .Pp
 .It Fl -color-diagnostics Ns = Ns Ar value

lld/test/ELF/cgprofile-txt.s

@@ -26,12 +26,12 @@
 # RUN: echo "TooManyPreds10 TooManyPreds 11" >> %t.call_graph
 # RUN: ld.lld -e A %t --call-graph-ordering-file %t.call_graph --call-graph-profile-sort=hfsort -o %t2
 # RUN: llvm-readobj --symbols %t2 | FileCheck %s
-## --call-graph-profile-sort=hfsort is the default.
-# RUN: ld.lld -e A %t --call-graph-ordering-file %t.call_graph -o %t2b
-# RUN: cmp %t2 %t2b
 
 # RUN: ld.lld -e A %t --call-graph-ordering-file %t.call_graph --call-graph-profile-sort=cdsort -o %t2
 # RUN: llvm-readobj --symbols %t2 | FileCheck %s --check-prefix=CDSORT
+## --call-graph-profile-sort=cdsort is the default.
+# RUN: ld.lld -e A %t --call-graph-ordering-file %t.call_graph -o %t2b
+# RUN: cmp %t2 %t2b
 
 # RUN: not ld.lld -e A %t --call-graph-ordering-file %t.call_graph --call-graph-profile-sort=sort \
 # RUN:   -o /dev/null 2>&1 | FileCheck %s --check-prefix=UNKNOWN