[LLVMdev] Plea for help

[Chris Lattner]

On Tue, 4 May 2004, Finn S Andersen wrote:
> Chris wrote in a followup:
>
> > Can you send the output of 'llc -o - foo.bc -debug -print-machineinstrs'?
>
>
> Attached as "linscan". (But added the "-regalloc=linearscan" to provoke
> the error).

Yes, that's exactly what I meant... thanks for reading my mind!  :)

It looks like this is where things start to go downhill
(LiveIntervals.cpp:559):

LiveIntervals::Interval::Interval(unsigned r)
    : reg(r),
      weight((MRegisterInfo::isPhysicalRegister(r) ?
              std::numeric_limits<float>::infinity() : 0.0F))
{


For a physical register (EDX in this case) it appears that the interval is
being created, but gets a 0 weight instead of an infinity weight.  This
implies that the MRegisterInfo::isPhysicalRegister might have an issue, or
std::numeric_limits has an issue.

Could you try compiling and running this program:

---
#include <limits>
#include <iostream>
int main() {
  std::cerr << std::numeric_limits<float>::infinity() << "\n";
}
---

If that prints 'inf', then check include/llvm/Target/MRegisterInfo.h, and
make sure you see something like this in it:

  /// isPhysicalRegister - Return true if the specified register number is in
  /// the physical register namespace.
  static bool isPhysicalRegister(unsigned Reg) {
    assert(Reg && "this is not a register!");
    return Reg < FirstVirtualRegister;
  }


If that looks fine, try changing LiveIntervals::Interval::Interval in
lib/CodeGen/LiveIntervals.cpp to this:

LiveIntervals::Interval::Interval(unsigned r)
    : reg(r),
      weight((MRegisterInfo::isPhysicalRegister(r) ?
              std::numeric_limits<float>::infinity() : 0.0F))
{
  std::cerr << "Created interval for reg " << reg << " weight = " << weight
            << "\n";
  assert(r < 1024 || weight > 1 && "physreg or weight incorrectly computed!");
}


And send me the output of -debug -print-machineinstrs -regalloc-linearscan
again.  :)

Thanks, I hope we can get this resolved once and for all!

-Chris

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