[LLVMdev] Patch - big stackframes on SPU

Raiskila Kalle kalle.raiskila at nokia.com
Fri Feb 26 02:25:38 PST 2010

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.  


> 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:

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...


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