[PATCH] D13358: InstSimplify: Fold comparisons between allocas and arguments under certain circumstances

[Hans Wennborg via llvm-commits]

hans added a comment.

Actually, requiring that the alloca is only used in a single comparison makes everything much simpler. I also verified that it didn't make the optimization fire any less over Chromium (this patch reduced binary size by about 10k).

Also, this means we don't need to trace the Argument value. It's fine if it escapes, because we know it can't be compared against any values based on the alloca since only allow one cmp.

And now that we don't need to be able to trace the non-Argument side of the comparison, it means we don't have to restrains that to just Arguments, in fact under these conditions we can act as if the alloca doesn't alias pointers based on any other value, including e.g. pointers from malloc. (This is similar to the "an alloca which is only used in a single cmp can be trivially folded" argument in the patch Philip sent to the list.)

I think this makes the optimization much more powerful. (Unfortunately it only knocked 100 more bytes of the Chromium build.) I'll get an updated patch out tomorrow.


http://reviews.llvm.org/D13358