[PATCH] D15722: [WIP][Polly] SSA Codegen

[Michael Kruse via llvm-commits]

Meinersbur added a comment.

In http://reviews.llvm.org/D15722#400494, @jdoerfert wrote:

> Yes, but there is little evidence so far that we generate "too many"
>  unused PHIs with this patch for interesting code.


With 'it' in my second paragraph I was referring to http://reviews.llvm.org/D15722 (without backtracking), i.e. was trying to express exactly this. Sorry for my ambiguous writing.

Generally we should be looking for arguments/proof that some code does not introduce scaling issues instead of waiting for evidence that there is one. Otherwise the evidence will come in form of users complaining about excessive compilation time with their sources after a release.

However, in this case I am not too much concerned. Worst case would be to have many Instructions at the beginning of the scop and a PHI node for each of them at each join point. mem2reg might not perform better when we do it with the current implementation. Therefore I suggest to leave it with the current implementation (i.e. http://reviews.llvm.org/D15722).


http://reviews.llvm.org/D15722