Limit the icmp+phi merging optimization to the cases where it is profitable:

don't make i1 phis when it won't be possible to eliminate them.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52097 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 12 insertions, 4 deletions

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 67c40fe..3b181c8 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -5043,8 +5043,12 @@ Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) {
     if (Instruction *LHSI = dyn_cast<Instruction>(Op0))
       switch (LHSI->getOpcode()) {
       case Instruction::PHI:
-        if (Instruction *NV = FoldOpIntoPhi(I))
-          return NV;
+        // Only fold fcmp into the PHI if the phi and fcmp are in the same
+        // block.  If in the same block, we're encouraging jump threading.  If
+        // not, we are just pessimizing the code by making an i1 phi.
+        if (LHSI->getParent() == I.getParent())
+          if (Instruction *NV = FoldOpIntoPhi(I))
+            return NV;
         break;
       case Instruction::SIToFP:
       case Instruction::UIToFP:
@@ -5348,8 +5352,12 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
         break;
 
       case Instruction::PHI:
-        if (Instruction *NV = FoldOpIntoPhi(I))
-          return NV;
+        // Only fold icmp into the PHI if the phi and fcmp are in the same
+        // block.  If in the same block, we're encouraging jump threading.  If
+        // not, we are just pessimizing the code by making an i1 phi.
+        if (LHSI->getParent() == I.getParent())
+          if (Instruction *NV = FoldOpIntoPhi(I))
+            return NV;
         break;
       case Instruction::Select: {
         // If either operand of the select is a constant, we can fold the