[PATCH] D117110: [InstCombine] try to fold binop with phi operands

[Mingming Liu via Phabricator via llvm-commits]

luna added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp:1329-1334
+  Builder.SetInsertPoint(PredBlockBranch);
+  Value *NewBO = Builder.CreateBinOp(BO.getOpcode(),
+                                     Phi0->getIncomingValueForBlock(OtherBB),
+                                     Phi1->getIncomingValueForBlock(OtherBB));
+  if (auto *NotFoldedNewBO = dyn_cast<BinaryOperator>(NewBO))
+    NotFoldedNewBO->copyIRFlags(&BO);
----------------
I'm wondering if it's idiomatic to validate that this instruction could also be simplified away in later iterations of instruction-combine, and only proceed with the fold if yes.

e.g., in https://godbolt.org/z/fKfondqrn, `%res = or i64 %retval.sroa.3.0.extract.shift, %phi.cast` instruction is inserted into `if.then` block, and could be simplified away.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D117110/new/

https://reviews.llvm.org/D117110