Change 6420645 causes SIGBUS during deoptimisation at a safepoint on 64bit-SPARC

[Tom Rodriguez]

> The problem can be easily solved by switching back to the old
> implementation of frame::oopmapreg_to_location(), but I assume there
> was a rational behind the change and that the new implementation is
> probably necessary for compressed oops (at least that's what the whole
> change was all about). So I dug a little further and found that in my
> opinion the root cause of the whole problem is the strange numbering
> of the 16 upper double registers in sparc.ad. They are defined as
> follows:
>
> reg_def R_D32x(SOC, SOC, Op_RegD,255, F32->as_VMReg());
> reg_def R_D32 (SOC, SOC, Op_RegD,  1, F32->as_VMReg()->next());
> reg_def R_D34x(SOC, SOC, Op_RegD,255, F34->as_VMReg());
> reg_def R_D34 (SOC, SOC, Op_RegD,  3, F34->as_VMReg()->next());
> ...
> reg_def R_D62x(SOC, SOC, Op_RegD,255, F62->as_VMReg());
> reg_def R_D62 (SOC, SOC, Op_RegD, 31, F62->as_VMReg()->next());

I don't really know why it's done this way.  It's certainly not  
consistent with the others.  If it all works better I'd be ok with  
correcting.

> PS: while I was hunting the error, I also stumbled across the
> following code in RegisterSaver::save_live_registers():
>
>  // Save all the FP registers
>  int offset = d00_offset;
>  for( int i=0; i<64; i+=2 ) {
>    FloatRegister f = as_FloatRegister(i);
>    __ stf(FloatRegisterImpl::D,  f, SP, offset+STACK_BIAS);
>    map->set_callee_saved(VMRegImpl::stack2reg(offset>>2), f- 
> >as_VMReg());
>    if (true) {
>      map->set_callee_saved(VMRegImpl::stack2reg((offset +
> sizeof(float))>>2), f->as_VMReg()->next());
>    }
>    offset += sizeof(double);
>  }

That would probably be ok too.

tom

>
> In my opinion, this could be changed to:
>
>  // Save all the FP registers
>  int offset = d00_offset;
>  for( int i=0; i<64; i+=2 ) {
>    FloatRegister f = as_FloatRegister(i);
>    __ stf(FloatRegisterImpl::D,  f, SP, offset+STACK_BIAS);
>    map->set_callee_saved(VMRegImpl::stack2reg(offset>>2), f- 
> >as_VMReg());
>    if (i < 32) { // VS 2009-08-31: the 16 upper double registers
> can't be used as floats anyway
>      map->set_callee_saved(VMRegImpl::stack2reg((offset +
> sizeof(float))>>2), f->as_VMReg()->next());
>    }
>    offset += sizeof(double);
>  }
>
> because the 16 upper double registers can't be used as floats anyway.
> Again, I didn't found any regression in my few tests. What do you
> think?
> <DeoptTest.java>