[llvm] r181927 - Implement PPC counter loops as a late IR-level pass

[Hal Finkel]

----- Original Message -----
> Hal Finkel <hfinkel at anl.gov> wrote:
> 
> > Implement PPC counter loops as a late IR-level pass
> 
> This seems to have introduced two new test-suite failures in 32-bit
> mode:
> SingleSource/Benchmarks/Adobe-C++/simple_types_constant_folding
> SingleSource/Benchmarks/Adobe-C++/simple_types_loop_invariant
> 
> Looking at the first one, it crashes on the line:
> 
>         ::fill(data64, data64+SIZE, int64_t(init_value));
> 
> where the variables are:
> 
> const int SIZE  = 8000;
> double init_value = 1.0;
> int64_t data64[SIZE];
> 
> The generated assembly for this line is:
> 
>    0x10002f14 <+8536>:  lis     r3,4100
>    0x10002f18 <+8540>:  li      r4,2000
>    0x10002f1c <+8544>:  li      r30,0
>    0x10002f20 <+8548>:  lfd     f1,-6872(r3)
>    0x10002f24 <+8552>:  mtctr   r4
>    0x10002f28 <+8556>:  bl      0x1002cdc0 <__fixdfdi at plt>
>    0x10002f2c <+8560>:  lis     r5,4102
>    0x10002f30 <+8564>:  addi    r5,r5,22096
>    0x10002f34 <+8568>:  mr      r6,r5
>    0x10002f38 <+8572>:  stwux   r3,r6,r30
>    0x10002f3c <+8576>:  addi    r30,r30,32
>    0x10002f40 <+8580>:  stw     r4,12(r6)
>    0x10002f44 <+8584>:  stw     r3,8(r6)
>    0x10002f48 <+8588>:  stw     r4,4(r6)
>    0x10002f4c <+8592>:  stw     r4,28(r6)
>    0x10002f50 <+8596>:  stw     r3,24(r6)
>    0x10002f54 <+8600>:  stw     r4,20(r6)
>    0x10002f58 <+8604>:  stw     r3,16(r6)
>    0x10002f5c <+8608>:  bdnz    0x10002f34 <main(int, char**)+8568>
> 
> Note how 0x1002f24 sets up CTR to hold the loop counter, but this is
> then clobbered by the function call to __fixdfdi.
> 
> > The most fragile part of this new implementation is that
> > interfering uses
> of
> > the counter register must be detected on the IR level (and, on PPC,
> > this
> also
> > includes any indirect branches in addition to function calls).
> 
> Does this maybe need anything special to detect libgcc helper
> function
> calls?

In PPCCTRLoops.cpp:

      } else if (isa<UIToFPInst>(J) || isa<SIToFPInst>(J) ||
                 isa<FPToUIInst>(J) || isa<FPToSIInst>(J)) {
        CastInst *CI = cast<CastInst>(J);
        if (CI->getSrcTy()->getScalarType()->isPPC_FP128Ty() ||
            CI->getDestTy()->getScalarType()->isPPC_FP128Ty())
          return MadeChange;

Is seems like this needs to be expanded to also pick up f64 cases when in 32-bit mode. Thanks!

 -Hal

> 
> 
> Bye,
> Ulrich
> 
>