[PATCH] D145299: [InstCombine] Generate better code for std::bit_ceil

[Kazu Hirata via Phabricator via llvm-commits]

kazu marked an inline comment as done.
kazu added a comment.

I've updated the patch.  Please take a look.  Thanks!



================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp:3197
+  auto MatchForward = [&](Value *CommonAncestor) {
+    const APInt *C = nullptr;
+    if (match(CtlzOp, m_Add(m_Specific(CommonAncestor), m_APInt(C)))) {
----------------
nikic wrote:
> Check `CommonAncestor == CtlzOp` here and then drop the first `if` below? So it's one MatchForward plus one MatchForward after peeking through add?
I am not sure if I understand your suggestion here.  Could you elaborate?  We have three possibilities:

- Peek through an `add`
- `MatchForward`
- Peek through an `add` and `MatchForward`

I cannot just drop the first `if` below.  I need to check for a specific operand `m_Add(m_Specific(CtlzOp), ...)`.


Repository:
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https://reviews.llvm.org/D145299