[PATCH] D11648: InstCombinePHI: Partial simplification of identity operations

[David Majnemer via llvm-commits]

majnemer added inline comments.

================
Comment at: lib/Transforms/InstCombine/InstCombinePHI.cpp:850-855
@@ +849,8 @@
+  // since it's not obvious if that'd be a performance win and if it'd be safe.
+  if (const auto *BI = dyn_cast<BranchInst>(Terminator)) {
+    if (BI->isConditional() && (PNUser.getOpcode() == Instruction::UDiv ||
+                                PNUser.getOpcode() == Instruction::SDiv))
+      return nullptr;
+  } else
+    return nullptr;
+
----------------
I think the correct logic would be:
  // We can only push the instruction to a predecessor if our predecessor is guaranteed to have a single, unique successor.
  if (BB->getUniqueSuccessor() != PN.getParent())
    return nullptr;

It should always be safe to hoist the instruction so long as it is inserted before the terminator.


Repository:
  rL LLVM

http://reviews.llvm.org/D11648