[PATCH] D127628: [NewGVN][LoadCoercion][3/3] Replace load with a phi node

[Jay Foad via Phabricator via llvm-commits]

foad added a comment.

In example 2 you insert a new instruction `%V1 = load i32, i32* %P` at the end of BB2. I'm not sure this is safe in general. For example, if BB2 has other successors:

  BB1     BB2
     \   /   \
      BB3     BB4

then the new load instruction will be executed even if BB2 is going to branch to BB4, and in that case the load might trap.

As another example, what if BB3 looked like this:

  BB3:
    call @foo // this function never returns
    %V = load i32, i32* %P // this load always traps

If you insert a load at the end of BB2 then it will trap //before// calling `@foo`, which changes the behaviour of the program.


Repository:
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  https://reviews.llvm.org/D127628/new/

https://reviews.llvm.org/D127628