[PATCH] D28593: Update loop branch_weight metadata after loop rotation.

[Dehao Chen via Phabricator via llvm-commits]

danielcdh added inline comments.


================
Comment at: test/Transforms/LoopRotate/loop-rotate-pgo.ll:60
+; CHECK: !0 = !{!"branch_weights", i32 28, i32 7}
+; CHECK: !1 = !{!"branch_weights", i32 7, i32 1}
+!0 = !{!"branch_weights", i32 35, i32 7}
----------------
I'm a little confused the logic here. For the following code:

L1:
if (cond) { // taken probability 7/35
  stmt;
  goto L1;
}

The loop rotate originally transforms it to:

if (cond) { // taken probability 7/35
L1:
  stmt;
  if (cond) { // taken probability 7/35
    goto L1;
  }
}

Your patch change it to:

if (cond) { // taken probability 7/28
L1:
  stmt
  if (cond) { // taken probability 1/7
    goto L1;
  }
}

Assuming "cond" has fixed taken probability, the original probability seems more correct to me? Or am I missing something?


https://reviews.llvm.org/D28593