From b29714a10af94b6daae437e48a82ae32675f79cb Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Thu, 27 Nov 2008 07:43:12 +0000 Subject: move MergeBasicBlockIntoOnlyPred to Transforms/Utils. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60162 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Utils/Local.cpp | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) (limited to 'lib/Transforms/Utils/Local.cpp') diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp index ed67c5eaaa..efb902267d 100644 --- a/lib/Transforms/Utils/Local.cpp +++ b/lib/Transforms/Utils/Local.cpp @@ -200,3 +200,36 @@ bool llvm::dceInstruction(BasicBlock::iterator &BBI) { } return false; } + +//===----------------------------------------------------------------------===// +// Control Flow Graph Restructuring... +// + +/// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its +/// predecessor is known to have one successor (DestBB!). Eliminate the edge +/// between them, moving the instructions in the predecessor into DestBB and +/// deleting the predecessor block. +/// +void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB) { + // If BB has single-entry PHI nodes, fold them. + while (PHINode *PN = dyn_cast(DestBB->begin())) { + Value *NewVal = PN->getIncomingValue(0); + // Replace self referencing PHI with undef, it must be dead. + if (NewVal == PN) NewVal = UndefValue::get(PN->getType()); + PN->replaceAllUsesWith(NewVal); + PN->eraseFromParent(); + } + + BasicBlock *PredBB = DestBB->getSinglePredecessor(); + assert(PredBB && "Block doesn't have a single predecessor!"); + + // Splice all the instructions from PredBB to DestBB. + PredBB->getTerminator()->eraseFromParent(); + DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList()); + + // Anything that branched to PredBB now branches to DestBB. + PredBB->replaceAllUsesWith(DestBB); + + // Nuke BB. + PredBB->eraseFromParent(); +} -- cgit v1.2.3-18-g5258