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/cfe/trunk@133435 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/CGCleanup.cpp b/lib/CodeGen/CGCleanup.cpp
index 17a55f09ca453ad13b33e902cfac154772c8310a..f75253bf78839945219298d845a1e5df2ca9ac33 100644 (file)
--- a/lib/CodeGen/CGCleanup.cpp
+++ b/lib/CodeGen/CGCleanup.cpp
@@ -420,13 +420,13 @@ static llvm::BasicBlock *SimplifyCleanupEntry(CodeGenFunction &CGF,
   // Kill the branch.
   Br->eraseFromParent();
 
-  // Merge the blocks.
-  Pred->getInstList().splice(Pred->end(), Entry->getInstList());
-
   // Replace all uses of the entry with the predecessor, in case there
   // are phis in the cleanup.
   Entry->replaceAllUsesWith(Pred);
 
+  // Merge the blocks.
+  Pred->getInstList().splice(Pred->end(), Entry->getInstList());
+
   // Kill the entry block.
   Entry->eraseFromParent();