[LLVMbugs] [Bug 4566] New: Invalid asmprinting for Thumb RSB instruction [ generic asmprinter construction problem?]

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=4566

           Summary: Invalid asmprinting for Thumb RSB instruction [generic
                    asmprinter construction problem?]
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Backend: ARM
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: asl at math.spbu.ru
                CC: llvmbugs at cs.uiuc.edu


Consider the attached bitcode. Currently we're producing the following
instructions:

.Llabel18:
        lsls r5, r2
        rsbs r2, r5
        orrs r4, r2

which is definitely wrong in Thumb1 mode. In fact, tRSB instruction has the
following assembler string: "rsb", " $dst, $src, #0", but the #0 operand is
never emitted. This seems to be due to some weirdness in asmprinter emission:
AMAsmPrinter::printInstruction() function contains 2 entries for tRSB:

  case 45:
    // tMOVi8, tMVN, tRSB
    printPredicateOperand(MI, 3);
    O << " ";
    printOperand(MI, 0);
    O << ", ";
    printOperand(MI, 2);
    EmitComments(*MI);
    O << "\n";
    return true;
    break;
  }

and

  case 22:
    // tRSB
    O << ", #0";
    EmitComments(*MI);
    O << "\n";
    return true;
    break;

note that "return true' in the first case makes it impossible to reach the
second fragment.


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