[llvm-commits] [PATCH] llvm-stress fixes

[Eli Friedman]

On Fri, Apr 6, 2012 at 8:31 AM, nobled <nobled at dreamwidth.org> wrote:
> Attached are some fixes for assertion failures running llvm-stress.
> However, there's a third problem that's uncovered once these get
> applied.
>
> Now, with certain combinations of options, I get this assertion:
> bin/llvm-stress -seed=1 -size=500 -generate-fp128 -generate-half-float
> -generate-ppc-fp128 -generate-x86-fp80 -generate-x86-mmx -o /dev/null
> llvm-stress: /llvm/lib/VMCore/Instructions.cpp:2719:
> llvm::FPExtInst::FPExtInst(llvm::Value*, llvm::Type*, const
> llvm::Twine&, llvm::Instruction*): Assertion `castIsValid(getOpcode(),
> S, Ty) && "Illegal FPExt"' failed.
>
> ...because it's trying to use an fpext to cast from a ppc_fp128 type
> to an IEEE-standard fp128 type.
>
> Which raises the question, just how *are* you supposed to cast between
> those types?  fptrunc asserts for the same reason; they're both 128
> bits. But they don't look like they can just be bitcast to each other
> either.

There isn't any straightforward way in LLVM IR to convert between the
two types, although you can trunc to double and re-extend.  I don't
even know how you would actually implement the conversion, though, so
it's probably okay to just avoid generating it.

For the random-float patch, it would be nice to make it generate
infinity and NaN's more frequently; otherwise, the patches seem okay.

-Eli