[LLVMdev] Patch - big stackframes on SPU

[Scott Michel]

Here's today's status:

Before I commit patches for big stacks, need to get the register  
scavenging assert patch committed. That means making the existing test  
cases work before the regscav patch gets committed. To do this means  
looking into why varargs doesn't cause a frame to be set up when  
prolog/epilog code is emitted (the spills to the stack happen just  
fine, but $sp is not adjusted.)

"The Big Flick": need to look at varargs handling and why a frame  
isn't being emitted.


-scooter

On Feb 26, 2010, at 2:25 AM, Raiskila Kalle wrote:

> Chris Lattner skrev:
>> On Feb 22, 2010, at 6:08 AM, Kalle.Raiskila at nokia.com wrote:
>>> currently the SPU backend does not handle big stack frames (>16*511
>>> bytes) nicely. llc asserts on malformed machine instructions.  
>>> (Assertion `MI->getOperand(OpNo).isImm() && "printDFormAddr first  
>>> operand is not immediate")
>> Sounds fine to me in general.  Please write a testcase for this
>> though.
>
> Attached.
>
>
>> Also, this patch causes the CodeGen/CellSPU/call.ll
>> regression test to fail.
>
> Oops. Sorry about that. I promise to inspect output of 'make check'  
> more thoroughly in the future.
> This is now discussed in this thread:
> http://lists.cs.uiuc.edu/pipermail/llvmdev/2010-February/029706.html
>
>
> But the CodeGen/CellSPU/call.ll is not the only one that fails.  
> Three other tests from CodeGen/CellSPU fail also. The cause of these  
> is the enabling of the register scavenger. It allocates the  
> emergency spill slot from the stack, and in doing so function  
> prologue and epilogue gets injected into some functions that do not  
> use stack at all and thus wouldn't have a prologue or epilogue in  
> the first place. (Seems that all test case failures are due to this  
> - not bad code or asserts). But inserting redundant code ofcourse  
> bloats the generated code...
>
> Would it be possible to conditionally enable the register scavenger  
> only if the function has a big stack? It now gets unconditionally  
> enabled in  SPURegisterInfo::requiresRegisterScavenging(const  
> MachineFunction &MF).
> Just checking MF.getFrameInfo()->getStackSize() here doesn't seem to  
> be the solution...
>
>
> kalle
>
> <bigstack.ll>