[PATCH] D124118: [Peephole-Opt] For one kind of test-after-add pattern, eliminates test if it's correct to do so.

[David Li via Phabricator via llvm-commits]

davidxl added a comment.

I suspect there is something else going on.

The following case works fine without the patch.

define dso_local noundef i64 @_Z3fooPlll(ptr nocapture noundef %0, i64 noundef %1, i64 noundef %2) local_unnamed_addr #0 {

  %4 = load i64, ptr %0, align 8
  %5 = and i64 %4, 3
  %6 = icmp eq i64 %5, 0
  %7 = select i1 %6, i64 %1, i64 %2
  store i64 %7, ptr %0, align 8
  ret i64 %5

}

However a simple change below to replace the operand %2 in the select with %5 (output of and operation), then it stops working.

define dso_local noundef i64 @_Z3fooPlll(ptr nocapture noundef %0, i64 noundef %1, i64 noundef %2) local_unnamed_addr #0 {

  %4 = load i64, ptr %0, align 8
  %5 = and i64 %4, 3
  %6 = icmp eq i64 %5, 0
  %7 = select i1 %6, i64 %1, i64 %5
  store i64 %7, ptr %0, align 8
  ret i64 %5

}

Can you investigate the difference?  The behavior difference on ARM is also worth comparing with.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D124118/new/

https://reviews.llvm.org/D124118