[LLVMbugs] [Bug 7226] New: [ARM JIT] ARM JIT couldn't emit constant pool entry for "ConstantVector" and "ConstantArray"

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=7226

           Summary: [ARM JIT] ARM JIT couldn't emit constant pool entry
                    for "ConstantVector" and "ConstantArray"
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: ARM
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: sliao at google.com
                CC: llvmbugs at cs.uiuc.edu


In file lib/Target/ARM/ARMCodeEmitter.cpp, we found this line at the end of the
function "ARMCodeEmitter::emitConstPoolInstruction(const MachineInstr &MI)":

   llvm_unreachable("Unable to handle this constantpool entry!");

ARM JITting will reach this "unreachable" line when JITting a simple program
below:

int main(int argc, char** argv) {
  if(argc == 10000) {
    int i;
    float ident[16];
    float masterscale = 0.0041f;// / (gXOffset * 4.f + 1.f);

    int now = argc;
    timedelta = ((float)(now - lastuptime)) / 44.f;
    lastuptime = now;
    if (timedelta > 3) {
        // Limit the step adjustment factor to 3, so we don't get a sudden jump
        // after coming back from sleep.
        timedelta = 3;
    }

    i = gPreset;
    if (i != currentpreset) {
        currentpreset = i;
        int rgb = gBackCol;
        makeTextures();
    }
  }

  if(argc > 1)
      gTextureSwap = 1;
  else
      gTextureSwap = 0;

  if (gTextureSwap != 0) 
      scale[0] = .25f;
  else 
      scale[0] = 4.f;

  printf("%d %f\n", gTextureSwap, scale[0]);
  return 55;
}

The program is adapted from an internal clouds.c, so we can ignore the "if
(argc ==10000)" part. 

Note that the 0.25f and 4.f in the code above will become ConstantArray of 2
elements. The first element will be 0.25f, while the second, 4.f. ConstantArray
and ConstantVector should be implemented.

Our fix is to replace the last case in
"ARMCodeEmitter::emitConstPoolInstruction(const MachineInstr &MI)" with a
function call to "emitConstantToMemory()". This new function
"emitConstantToMemory" is defined as follows.

void ARMCodeEmitter::emitConstantToMemory(unsigned CPI, const Constant* C) {
  DEBUG({
      errs() << "  ** Constant pool #" << CPI << " @ "
             << (void*)MCE.getCurrentPCValue() << " ";
      if (const Function *F = dyn_cast<Function>(C))
        errs() << F->getName();
      else
        errs() << *C;
      errs() << '\n';
    });

  if (const GlobalValue *GV = dyn_cast<GlobalValue>(C)) {
    emitGlobalAddress(GV, ARM::reloc_arm_absolute, isa<Function>(GV), false);
    emitWordLE(0);
  } else if (const ConstantInt *CI = dyn_cast<ConstantInt>(C)) {
    uint32_t Val = *(uint32_t*)CI->getValue().getRawData();
    emitWordLE(Val);
  } else if (const ConstantFP *CFP = dyn_cast<ConstantFP>(C)) {
    if (CFP->getType()->isFloatTy())
      emitWordLE(CFP->getValueAPF().bitcastToAPInt().getZExtValue());
    else if (CFP->getType()->isDoubleTy())
      emitDWordLE(CFP->getValueAPF().bitcastToAPInt().getZExtValue());
    else {
      llvm_unreachable("Unable to handle this constantpool entry!");
    }
  } else if (const ConstantVector* CV = dyn_cast<ConstantVector>(C)) {
    for (unsigned i=0;i<CV->getNumOperands();i++)
      emitConstantToMemory(CPI, CV->getOperand(i));
  } else if (const ConstantArray* CA = dyn_cast<ConstantArray>(C)) {
    for (unsigned i=0;i<CA->getNumOperands();i++)
      emitConstantToMemory(CPI, CA->getOperand(i));
  } else {
    llvm_unreachable("Unable to handle this constantpool entry!");
  }

  return;
}

This will fix the unreachable problem above, which means that we will no longer
reach the line llvm_unreachable("Unable to handle this constantpool entry!").

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