Allow target to specify prefix for labels

[arsenm]

Summary

Use the MCAsmInfo instead of the DataLayout, and allow
specifying a custom prefix for labels specifically. HSAIL
requires that labels begin with @, but global symbols with &.

[• rafael]

This is probably OK.

My only question is how long do you expect this to be dead code? That is, how long until we have a test with HSAIL showing the @ and & difference?

[arsenm]

In D6467#4, @rafael wrote:

This is probably OK.

My only question is how long do you expect this to be dead code? That is, how long until we have a test with HSAIL showing the @ and & difference?

The plan is to upstream the HSAIL target as soon as possible, which is once I've finished fixing a long list of problems with it. My hope is this will take < 3 months

[• rafael]

LGTM

[arsenm]

r223323 plus missing updates for places that reset it from the default

include/llvm/MC/MCAsmInfo.h

protected:
   // Print the EH begin symbol with an assignment. Defaults to false.
   bool UseAssignmentForEHBegin;
 
   /// This prefix is used for globals like constant pool entries that are
   /// completely private to the .s file and should not have names in the .o
   /// file.  Defaults to "L"
   const char *PrivateGlobalPrefix;
 
+  /// This prefix is used for labels for basic blocks. Defaults to the same as
+  /// PrivateGlobalPrefix.
+  const char *PrivateLabelPrefix;
+
   /// This prefix is used for symbols that should be passed through the
   /// assembler but be removed by the linker.  This is 'l' on Darwin, currently
   /// used for some ObjC metadata.  The default of "" meast that for this system
   /// a plain private symbol should be used.  Defaults to "".
   const char *LinkerPrivateGlobalPrefix;
 
   /// If these are nonempty, they contain a directive to emit before and after
   /// an inline assembly statement.  Defaults to "#APP\n", "#NO_APP\n"
public:
   /// printed.
   unsigned getCommentColumn() const { return 40; }
 
   const char *getCommentString() const { return CommentString; }
   const char *getLabelSuffix() const { return LabelSuffix; }
 
   bool useAssignmentForEHBegin() const { return UseAssignmentForEHBegin; }
   const char *getPrivateGlobalPrefix() const { return PrivateGlobalPrefix; }
+  const char *getPrivateLabelPrefix() const { return PrivateLabelPrefix; }
   bool hasLinkerPrivateGlobalPrefix() const {
     return LinkerPrivateGlobalPrefix[0] != '\0';
   }
   const char *getLinkerPrivateGlobalPrefix() const {
     if (hasLinkerPrivateGlobalPrefix())
       return LinkerPrivateGlobalPrefix;
     return getPrivateGlobalPrefix();
   }

lib/CodeGen/MachineBasicBlock.cpp

 
 /// getSymbol - Return the MCSymbol for this basic block.
 ///
 MCSymbol *MachineBasicBlock::getSymbol() const {
   if (!CachedMCSymbol) {
     const MachineFunction *MF = getParent();
     MCContext &Ctx = MF->getContext();
     const TargetMachine &TM = MF->getTarget();
-    const char *Prefix =
-        TM.getSubtargetImpl()->getDataLayout()->getPrivateGlobalPrefix();
+    const char *Prefix = Ctx.getAsmInfo()->getPrivateLabelPrefix();
     CachedMCSymbol = Ctx.GetOrCreateSymbol(Twine(Prefix) + "BB" +
                                            Twine(MF->getFunctionNumber()) +
                                            "_" + Twine(getNumber()));
   }
 
   return CachedMCSymbol;
 }
 

lib/MC/MCAsmInfo.cpp

MCAsmInfo::MCAsmInfo() {
   MaxInstLength = 4;
   MinInstAlignment = 1;
   DollarIsPC = false;
   SeparatorString = ";";
   CommentString = "#";
   LabelSuffix = ":";
   UseAssignmentForEHBegin = false;
   PrivateGlobalPrefix = "L";
+  PrivateLabelPrefix = PrivateGlobalPrefix;
   LinkerPrivateGlobalPrefix = "";
   InlineAsmStart = "APP";
   InlineAsmEnd = "NO_APP";
   Code16Directive = ".code16";
   Code32Directive = ".code32";
   Code64Directive = ".code64";
   AssemblerDialect = 0;
   AllowAtInName = false;