[LLVMdev] Register allocator segfault

[Vladimir Prus]

Hello,
this is another "allocator crashes hard when I pass wrong data to it" issue. 
Due to a bug, my machine code looked like this:

# Machine code for list_sequence():
  <fi #-2> is 4 bytes fixed at location [SP-24]
  <fi #-1> is 4 bytes fixed at location [SP-20]

entry (0x8060970, LLVM BB @0x805da88):
        %reg1024 = load <fi#-1>
        %reg1025 = load <fi#-2>
        setcc %reg1025, %reg1026

(so 'reg1026' is used before definition). It would be nice if register 
allocator responded with a nice 'register used before definition in 
instruction ....' message. What I get now is:

Program received signal SIGSEGV, Segmentation fault.
0x400c24d4 in llvm::MachineInstr::getParent (this=0x0)
    at MachineInstr.h:408
408     MachineInstr.h: No such file or directory.
        in MachineInstr.h
(gdb) up
#1  0x40f05f28 in llvm::LiveVariables::HandleVirtRegUse (
    this=0x8060270, VRInfo=@0x8061930, MBB=0x8060970, MI=0x80615d0)
    at ../../lib/CodeGen/LiveVariables.cpp:100
100       assert(MBB != VRInfo.DefInst->getParent() &&
(gdb) p VRInfo.DefInst
$1 = (llvm::MachineInstr *) 0x0
(gdb) up
#2  0x40f0678f in llvm::LiveVariables::runOnMachineFunction (
    this=0x8060270, MF=@0x8060888)
    at ../../lib/CodeGen/LiveVariables.cpp:214
214                 HandleVirtRegUse(getVarInfo(MO.getReg()), MBB, MI);
(gdb) p MO.getReg()
$3 = 1026

Of course, this is just a wish, and it looks like it's exactly what issue 408
(http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=408) is about.

- Volodya