[PATCH] D50061: [llvm-exegesis] Proposal to add Exegesis Configuration to td files.

[Guillaume Chatelet via Phabricator via llvm-commits]

gchatelet added a comment.

In https://reviews.llvm.org/D50061#1187159, @RKSimon wrote:

> I meant the X86 execution domain info:
>
> X86InstrInfo::getExecutionDomain(const MachineInstr &MI) const {
>
>   uint16_t domain = (MI.getDesc().TSFlags >> X86II::SSEDomainShift) & 3;


Ha I see, well it's very specific to X86 and would not work for other architectures.
Also it still doesn't tell much about the semantic of the instruction which is needed to come up with good testing strategies.

Ultimately I'd like llvm-exegesis to explore instructions and report the ones with varied execution time. Two use cases for this:

- Timing attacks <https://en.wikipedia.org/wiki/Timing_attack#Concept> identification,
- Arithmetic performance: floating point operations on subnormal / Inf / NaN may be slower than with normal float. For instance, `llvm-exegesis` currently reports unrealistic latencies for division (VDIVPDrr is 172 cycles on Skylake)


Repository:
  rL LLVM

https://reviews.llvm.org/D50061