[llvm-commits] [PATCH] x86 code emitter improvements for object files

[Chris Lattner]

On Jul 31, 2009, at 4:03 PM, Bruno Cardoso Lopes wrote:

> Hi all,
>
> The X86CodeEmitter has the following behaviour:
>
> 1) When emiting displacements:
> - Only use pc_relative relocations for x86_64 (globals, cstpools and  
> jmptables)
> - For x86, only uses pc_rel ou pic_re
> This two items above do not always work for ELF.

Hi Bruno,

I don't have an opinion about this patch specifically, but would it be  
possible to make the code emitter be driven off the asm operand flags  
instead of making equivalent decisions that have to mirror what isel  
does?

Specifically, MO.getTargetFlags() should tell the code emitter how to  
handle the CPI/JT/GA/ExtSym operands, X86ATTAsmPrinter.cpp has stuff  
like this:

   switch (MO.getTargetFlags()) {
   default:
     llvm_unreachable("Unknown target flag on GV operand");
   case X86II::MO_NO_FLAG:    // No flag.
     break;
   case X86II::MO_DARWIN_NONLAZY:
   case X86II::MO_DARWIN_HIDDEN_NONLAZY:
   case X86II::MO_DLLIMPORT:
   case X86II::MO_DARWIN_STUB:
     // These affect the name of the symbol, not any suffix.
     break;
   case X86II::MO_GOT_ABSOLUTE_ADDRESS:
     O << " + [.-";
     PrintPICBaseSymbol();
     O << ']';
     break;
   case X86II::MO_PIC_BASE_OFFSET:
   case X86II::MO_DARWIN_NONLAZY_PIC_BASE:
   case X86II::MO_DARWIN_HIDDEN_NONLAZY_PIC_BASE:
     O << '-';
     PrintPICBaseSymbol();
     break;
   case X86II::MO_TLSGD:     O << "@TLSGD";     break;
   case X86II::MO_GOTTPOFF:  O << "@GOTTPOFF";  break;
   case X86II::MO_INDNTPOFF: O << "@INDNTPOFF"; break;
   case X86II::MO_TPOFF:     O << "@TPOFF";     break;
   case X86II::MO_NTPOFF:    O << "@NTPOFF";    break;
   case X86II::MO_GOTPCREL:  O << "@GOTPCREL";  break;
   case X86II::MO_GOT:       O << "@GOT";       break;
   case X86II::MO_GOTOFF:    O << "@GOTOFF";    break;
   case X86II::MO_PLT:       O << "@PLT";       break;
   }

For example.  It would be better to base the encoding on this flag  
than checking things like Is64BitMode, IsPIC etc.

> This patch try to solve the 3 problems above to properly emit elf
> binaries for x86/x86_64. With
> this changes applied (together with elf improvements I've not commited
> yet) I was able
> to run 209/243 (83%) of SinglesSources using ELF object files emited  
> by LLC :)
> and with no regressions for JIT.

Wow, nice!!

-Chris