[PATCH] D32224: [LV] Remove redundant basic block split

[Gil Rapaport via Phabricator via llvm-commits]

gilr created this revision.
Herald added a subscriber: mzolotukhin.

This patch is part of D28975 <https://reviews.llvm.org/D28975>'s breakdown.

The process of generating the control flow guarding predicated instructions includes:
(1) a call to SplitBlock(), which splits the basic block after the predicated instruction, producing:

  --> HEAD -->  PRED --> TAIL -->

(2) a call to SplitBblockAndInsertIfThen() which splits the basic block before the predicated instruction into a "triangle", resulting
in a redundant basic block with an unconditional branch:

  --> HEAD -->  PRED --> MERGE --> TAIL -->
            +----------------------^

By removing (1) we get:

  --> HEAD -->  PRED --> MERGE/TAIL -->
            +--------------------^


https://reviews.llvm.org/D32224

Files:
  lib/Transforms/Vectorize/LoopVectorize.cpp


Index: lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- lib/Transforms/Vectorize/LoopVectorize.cpp
+++ lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -4516,14 +4516,15 @@
   for (auto KV : PredicatedInstructions) {
     BasicBlock::iterator I(KV.first);
     BasicBlock *Head = I->getParent();
-    auto *BB = SplitBlock(Head, &*std::next(I), DT, LI);
     auto *T = SplitBlockAndInsertIfThen(KV.second, &*I, /*Unreachable=*/false,
                                         /*BranchWeights=*/nullptr, DT, LI);
     I->moveBefore(T);
     sinkScalarOperands(&*I);
 
-    I->getParent()->setName(Twine("pred.") + I->getOpcodeName() + ".if");
-    BB->setName(Twine("pred.") + I->getOpcodeName() + ".continue");
+    BasicBlock *PredicatedBlock = I->getParent();
+    Twine BBNamePrefix = Twine("pred.") + I->getOpcodeName();
+    PredicatedBlock->setName(BBNamePrefix + ".if");
+    PredicatedBlock->getSingleSuccessor()->setName(BBNamePrefix + ".continue");
 
     // If the instruction is non-void create a Phi node at reconvergence point.
     if (!I->getType()->isVoidTy()) {


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D32224.95732.patch
Type: text/x-patch
Size: 1142 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20170419/0032ab20/attachment.bin>