[MC][BOLT] Add setter for AllowAtInName

[Amir]

Summary

Use the setter in BOLT to allow printing names with variant kind in the name
(e.g. "func@PLT").
Fixes BOLT buildbot tests that broke after D122516:
https://lab.llvm.org/buildbot/#/builders/215/builds/3595

[maksfb]

bolt/lib/Core/BinaryContext.cpp

165

nit

[efriedma]

If you look at LLVM itself, normally it refers to PLT entries using an MCSymbolRefExpr marked up with MCSymbolRefExpr::VK_PLT. Ideally, BOLT would do the same thing... but maybe not worth the effort. Symbols with an "@" sign shouldn't show up in practice on non-Windows targets.

[maksfb]

In D122694#3415490, @efriedma wrote:

If you look at LLVM itself, normally it refers to PLT entries using an MCSymbolRefExpr marked up with MCSymbolRefExpr::VK_PLT. Ideally, BOLT would do the same thing... but maybe not worth the effort. Symbols with an "@" sign shouldn't show up in practice on non-Windows targets.

Since BOLT operates on a post-link binary, it sees PLT entries created by the linker and marks them with "sym@PLT", i.e. there will be both - undefined "sym" and defined "sym@PLT". In theory, we can use VK_PLT, but on the surface it looks as it will create more problems for BOLT.

[Amir]

Address nit

bolt/lib/Core/BinaryContext.cpp

BinaryContext::createBinaryContext(const ObjectFile *File, bool IsPIC,
   std::unique_ptr<const MCRegisterInfo> MRI(
       TheTarget->createMCRegInfo(TripleName));
   if (!MRI)
     return createStringError(
         make_error_code(std::errc::not_supported),
         Twine("BOLT-ERROR: no register info for target ", TripleName));
 
   // Set up disassembler.
-  std::unique_ptr<const MCAsmInfo> AsmInfo(
+  std::unique_ptr<MCAsmInfo> AsmInfo(
       TheTarget->createMCAsmInfo(*MRI, TripleName, MCTargetOptions()));
   if (!AsmInfo)
     return createStringError(
         make_error_code(std::errc::not_supported),
         Twine("BOLT-ERROR: no assembly info for target ", TripleName));
+  // BOLT creates "func@PLT" symbols for PLT entries. In function assembly dump
+  // we want to emit such names as using @PLT without double quotes to convey
+  // variant kind to the assembler. BOLT doesn't rely on the linker so we can
+  // override the default AsmInfo behavior to emit names the way we want.
+  AsmInfo->setAllowAtInName(true);
 
   std::unique_ptr<const MCSubtargetInfo> STI(
       TheTarget->createMCSubtargetInfo(TripleName, "", FeaturesStr));
   if (!STI)
     return createStringError(
         make_error_code(std::errc::not_supported),
         Twine("BOLT-ERROR: no subtarget info for target ", TripleName));
 

llvm/include/llvm/MC/MCAsmInfo.h

public:
 
   const char *getInlineAsmStart() const { return InlineAsmStart; }
   const char *getInlineAsmEnd() const { return InlineAsmEnd; }
   const char *getCode16Directive() const { return Code16Directive; }
   const char *getCode32Directive() const { return Code32Directive; }
   const char *getCode64Directive() const { return Code64Directive; }
   unsigned getAssemblerDialect() const { return AssemblerDialect; }
   bool doesAllowAtInName() const { return AllowAtInName; }
+  void setAllowAtInName(bool V) { AllowAtInName = V; }
   bool doesAllowQuestionAtStartOfIdentifier() const {
     return AllowQuestionAtStartOfIdentifier;
   }
   bool doesAllowAtAtStartOfIdentifier() const {
     return AllowAtAtStartOfIdentifier;
   }
   bool doesAllowDollarAtStartOfIdentifier() const {
     return AllowDollarAtStartOfIdentifier;