Change how PHINodes store their operands.

Change PHINodes to store simple pointers to their incoming basic blocks,
instead of full-blown Uses.

Note that this loses an optimization in SplitCriticalEdge(), because we
can no longer walk the use list of a BasicBlock to find phi nodes. See
the comment I removed starting "However, the foreach loop is slow for
blocks with lots of predecessors".

Extend replaceAllUsesWith() on a BasicBlock to also update any phi
nodes in the block's successors. This mimics what would have happened
when PHINodes were proper Users of their incoming blocks. (Note that
this only works if OldBB->replaceAllUsesWith(NewBB) is called when
OldBB still has a terminator instruction, so it still has some
successors.)

llvm-svn: 133435

1 files changed, 16 insertions, 0 deletions

diff --git a/llvm/lib/VMCore/BasicBlock.cpp b/llvm/lib/VMCore/BasicBlock.cpp
index 3f1a6a99b64..7d470440aff 100644
--- a/llvm/lib/VMCore/BasicBlock.cpp
+++ b/llvm/lib/VMCore/BasicBlock.cpp
@@ -308,3 +308,19 @@ BasicBlock *BasicBlock::splitBasicBlock(iterator I, const Twine &BBName) {
   return New;
 }
 
+void BasicBlock::replaceSuccessorsPhiUsesWith(BasicBlock *New) {
+  TerminatorInst *TI = getTerminator();
+  if (!TI)
+    // Cope with being called on a BasicBlock that doesn't have a terminator
+    // yet. Clang's CodeGenFunction::EmitReturnBlock() likes to do this.
+    return;
+  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
+    BasicBlock *Succ = TI->getSuccessor(i);
+    for (iterator II = Succ->begin(); PHINode *PN = dyn_cast<PHINode>(II);
+         ++II) {
+      int i;
+      while ((i = PN->getBasicBlockIndex(this)) >= 0)
+        PN->setIncomingBlock(i, New);
+    }
+  }
+}