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.)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133435 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 1 deletions

diff --git a/include/llvm/BasicBlock.h b/include/llvm/BasicBlock.h
index 7e7c9e7694..b02c249c7e 100644
--- a/include/llvm/BasicBlock.h
+++ b/include/llvm/BasicBlock.h
@@ -110,7 +110,7 @@ public:
         Function *getParent()       { return Parent; }
 
   /// use_back - Specialize the methods defined in Value, as we know that an
-  /// BasicBlock can only be used by Users (specifically PHI nodes, terminators,
+  /// BasicBlock can only be used by Users (specifically terminators
   /// and BlockAddress's).
   User       *use_back()       { return cast<User>(*use_begin());}
   const User *use_back() const { return cast<User>(*use_begin());}
@@ -248,6 +248,10 @@ public:
   /// other than direct branches, switches, etc. to it.
   bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; }
 
+  /// replaceSuccessorsPhiUsesWith - Update all phi nodes in all our successors
+  /// to refer to basic block New instead of to us.
+  void replaceSuccessorsPhiUsesWith(BasicBlock *New);
+
 private:
   /// AdjustBlockAddressRefCount - BasicBlock stores the number of BlockAddress
   /// objects using it.  This is almost always 0, sometimes one, possibly but