[PATCH] D23824: [ADCE] Add handling of PHI nodes when removing control flow

[David Callahan via llvm-commits]

david2050 added a comment.

I ran this test:

  int foo(int a, int b, int N) {
    int j = 0;
    if (b) {
      int i;
      for (i = 0; i < N; i++)
        ;
      j = 1;
    }
    return j;
  }

compiled to bc and then processed:  opt -sroa -adce -adce-remove-loops  and it did successfully remove the loop.  I also tried this variant

  int foo(int b, int N) {
    int j = 0;
    if (b) {
      int i;
      j = 1;
      for (i = 0; i < N; i++)
        ;
    }
    return j;
  }

The final output for that one looked like:

  define i32 @foo(i32 %b, i32 %N) #0 {
    %1 = icmp ne i32 %b, 0
    br i1 %1, label %2, label %3
  
  ; <label>:2:                                      ; preds = %0
    br label %3
  
  ; <label>:3:                                      ; preds = %2, %0
    %j.0 = phi i32 [ 0, %0 ], [ 1, %2 ]
    ret i32 %j.0
  }


https://reviews.llvm.org/D23824