[Metarenamer] Use 'inst' as default name for instructions

[mkazantsev]

Summary

Currently we use 'tmp', which is also a keyword for FileCheck. It leads to this
annoying warning whenever a script for auto-generation of checks is used.
It is especially annoying that it happens to every test affected by metarenamer.

Just use another prefix for metarenamed names to avoid this.

[nikic]

InstNamer uses the i prefix, so maybe follow that lead?

[nikic]

See dd54432a0f5a6f042fa4d2db3094c6f02e5ad275 for the corresponding InstNamer change.

[mkazantsev]

In D144001#4125834, @nikic wrote:

InstNamer uses the i prefix, so maybe follow that lead?

It'll create confusion with types like i32. I.e. just from human-readability perspective, it'd blow my mind.

[spatel]

FWIW, I now regret using "i" when I updated InstNamer because i,l,1 are all starting to blur together with age. :)
How about "inst" for both? That's the common short form for an Instruction.

[mkazantsev]

inst sounds good to me.

[nikic]

LGTM

A thought I had is that we could also use the name of the instruction, producing something like %phi1 = phi i32 [ ... ]. This is something I often end up doing when manually cleaning up names. That makes things easier to follow than just numbering all instructions.

[mkazantsev]

In D144001#4128130, @nikic wrote:

LGTM

A thought I had is that we could also use the name of the instruction, producing something like %phi1 = phi i32 [ ... ]. This is something I often end up doing when manually cleaning up names. That makes things easier to follow than just numbering all instructions.

I'd also do it for loop headers and other stuff. Will do as a follow-up.

llvm/lib/Transforms/Utils/MetaRenamer.cpp

for (Argument &Arg : F.args())
     if (!Arg.getType()->isVoidTy())
       Arg.setName("arg");
 
   for (auto &BB : F) {
     BB.setName("bb");
 
     for (auto &I : BB)
       if (!I.getType()->isVoidTy())
-        I.setName("tmp");
+        I.setName("inst");
   }
 }
 
 void MetaRename(Module &M,
                 function_ref<TargetLibraryInfo &(Function &)> GetTLI) {
   // Seed our PRNG with simple additive sum of ModuleID. We're looking to
   // simply avoid always having the same function names, and we need to
   // remain deterministic.