Sort the incoming values in PHI nodes to match the predecessor order.

This helps expose duplicate PHIs, which will make it easier for them
to be eliminated.

llvm-svn: 85623

1 files changed, 19 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index 0ca3114c44d..e1741a00676 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -10980,6 +10980,25 @@ Instruction *InstCombiner::visitPHINode(PHINode &PN) {
       }
     }
   }
+
+  // Sort the PHI node operands to match the pred iterator order. This will
+  // help identical PHIs be eliminated by other passes. Other passes shouldn't
+  // depend on this for correctness however.
+  unsigned i = 0;
+  for (pred_iterator PI = pred_begin(PN.getParent()),
+       PE = pred_end(PN.getParent()); PI != PE; ++PI, ++i)
+    if (PN.getIncomingBlock(i) != *PI) {
+      unsigned j = PN.getBasicBlockIndex(*PI);
+      Value *VA = PN.getIncomingValue(i);
+      BasicBlock *BBA = PN.getIncomingBlock(i);
+      Value *VB = PN.getIncomingValue(j);
+      BasicBlock *BBB = PN.getIncomingBlock(j);
+      PN.setIncomingBlock(i, BBB);
+      PN.setIncomingValue(i, VB);
+      PN.setIncomingBlock(j, BBA);
+      PN.setIncomingValue(j, VA);
+    }
+
   return 0;
 }