[IR] Add PHINode::removeIncomingValueIf() (NFC)

Add an API that allows removing multiple incoming phi values based
on a predicate callback, as suggested on D157621.

This makes sure that the removal is linear time rather than quadratic,
and avoids subtleties around iterator invalidation.

I have replaced some of the more straightforward users with the new
API, though there's a couple more places that should be able to use it.

Differential Revision: https://reviews.llvm.org/D158064

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopSimplify.cpp b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
index 3e604fd..07e622b 100644
--- a/llvm/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
@@ -429,8 +429,8 @@ static BasicBlock *insertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader,
       PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
     }
     // Nuke all entries except the zero'th.
-    for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
-      PN->removeIncomingValue(e-i, false);
+    PN->removeIncomingValueIf([](unsigned Idx) { return Idx != 0; },
+                              /* DeletePHIIfEmpty */ false);
 
     // Finally, add the newly constructed PHI node as the entry for the BEBlock.
     PN->addIncoming(NewPN, BEBlock);