[PATCH] D54021: [LoopSimplifyCFG] Teach LoopSimplifyCFG to constant-fold branches and switches

[Dave Green via Phabricator via llvm-commits]

dmgreen added a comment.

Hello. I have an error from this, which I think may well be a knock-on affect for the code later in the pass. Something like this:

  define void @repo(i32 %size) {
  entry:
    br label %loop
  
  loop:
    %i = phi i32 [ 0, %entry ], [ %inc, %loop2 ]
    br i1 true, label %loop1, label %loop2
  
  loop1:
    call void @something()
    br label %loop2
  
  loop2:
    %phi = phi i32 [ 1, %loop ], [ 2, %loop1 ]
    %inc = add i32 %i, %phi
    %cmp = icmp ult i32 %inc, 3900
    br i1 %cmp, label %loop, label %end
  
  end:
    ret void
  }
  
  declare void @something()

The br i1 true is const-folded, but the %phi gets the wrong value, taking the 1 where it should be taking the 2.


Repository:
  rL LLVM

https://reviews.llvm.org/D54021