[PATCH] D151052: [LoopUnroll] Peel iterations based on select, and, or conditions

[Joshua Cao via Phabricator via llvm-commits]

caojoshua added inline comments.


================
Comment at: llvm/lib/Transforms/Utils/LoopPeel.cpp:352
+    MaxPeelCount =
+        std::min((unsigned)SC->getAPInt().getZExtValue() - 1, MaxPeelCount);
+
----------------
nikic wrote:
> Why is this code needed now?
Latch branch conditions can peel the entire loop.

```
for (i = 0; i < 4; ++i) {
  foo();
  // The backedge branch, i < 4, is known for all iterations, and could make us peel the entire loop
}
```

When peeling only branch instructions, we avoid this by ignoring the branch condition of the latch block. But with this patch, we don't ignore and/or's that are used by the latch branch.

I will take out and/or's from this patch as recommended, but I would still like to keep this code block here. It's not breaking and it avoids unnecessary transformations.




Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D151052/new/

https://reviews.llvm.org/D151052