[IPSCCP] Partial support for constrained intrinsics

[kpn]

Summary

This teaches the SCCP Solver about some of the constrained intrinsics by having them use the same codepaths as the non-constrained instructions.

Casting instructions along with the binary operators will come later.

[fhahn]

llvm/lib/IR/Instruction.cpp

694 ↗

(On Diff #394265)

I think this change is strictly independent of supporting constrained intrinsics in SCCP and should be separate I think.

llvm/test/Transforms/SCCP/strictfp-float-nan-simplification.ll

1 ↗

(On Diff #394265)

could you preocmmit the tests?

[nikic]

llvm/lib/IR/Instruction.cpp

694 ↗

(On Diff #394265)

I think it would be better to address this by switching SCCP to use isInstructionTriviallyDead() instead. In fact, if we switch SCCP and FunctionSpecialization, we can drop this method entirely, as these seem to be the only users. Don't really see why we need a second, worse implementation if this functionality.

[kpn]

Update for review comments. I've also reduced it down to just fcmp and fcmps having a functional impact. I don't have a good way to test the binary operators just yet.

[kpn]

Ping

[nikic]

Why isn't this already handled by ConstantFoldCall?