Little patch to turn (shl (add X, 123), 4) -> (add (shl X, 4), 123 << 4)

This triggers in cases of bitfield additions, opening opportunities for
future improvements.

llvm-svn: 16834

1 files changed, 3 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index 767fc9582b0..3febd1dd46f 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -2496,6 +2496,9 @@ Instruction *InstCombiner::visitShiftInst(ShiftInst &I) {
 
           switch (Op0BO->getOpcode()) {
           default: isValid = false; break;   // Do not perform transform!
+          case Instruction::Add:
+            isValid = isLeftShift;
+            break;
           case Instruction::Or:
           case Instruction::Xor:
             highBitSet = false;