[CodeGen] Add text section prefix for COFF object file

Text section prefix is created in CodeGenPrepare, it's file format independent implementation,  text section name is written into object file in TargetLoweringObjectFile, it's file format dependent implementation, port code of adding text section prefix to text section name from ELF to COFF.
Different with ELF that use '.' as concatenation character, COFF use '$' as concatenation character. That is, concatenation character is variable, so split concatenation character from text section prefix.
Text section prefix is existing feature of ELF, it can help to reduce icache and itlb misses, it's also make possible aggregate other compilers e.g. v8 created same prefix sections. Furthermore, the recent feature Machine Function Splitter (basic block level text prefix section) is based on text section prefix.

Reviewed By: pengfei, rnk

Differential Revision: https://reviews.llvm.org/D92073

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 4c8caa0..2e32eab 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -621,7 +621,7 @@ getELFSectionNameForGlobal(const GlobalObject *GO, SectionKind Kind,
   bool HasPrefix = false;
   if (const auto *F = dyn_cast<Function>(GO)) {
     if (Optional<StringRef> Prefix = F->getSectionPrefix()) {
-      Name += *Prefix;
+      raw_svector_ostream(Name) << '.' << *Prefix;
       HasPrefix = true;
     }
   }
@@ -1573,6 +1573,10 @@ MCSection *TargetLoweringObjectFileCOFF::SelectSectionForGlobal(
       MCSymbol *Sym = TM.getSymbol(ComdatGV);
       StringRef COMDATSymName = Sym->getName();
 
+      if (const auto *F = dyn_cast<Function>(GO))
+        if (Optional<StringRef> Prefix = F->getSectionPrefix())
+          raw_svector_ostream(Name) << '$' << *Prefix;
+
       // Append "$symbol" to the section name *before* IR-level mangling is
       // applied when targetting mingw. This is what GCC does, and the ld.bfd
       // COFF linker will not properly handle comdats otherwise.
@@ -2020,7 +2024,7 @@ static MCSectionWasm *selectWasmSectionForGlobal(
   if (const auto *F = dyn_cast<Function>(GO)) {
     const auto &OptionalPrefix = F->getSectionPrefix();
     if (OptionalPrefix)
-      Name += *OptionalPrefix;
+      raw_svector_ostream(Name) << '.' << *OptionalPrefix;
   }
 
   if (EmitUniqueSection && UniqueSectionNames) {