minor cleanup to SROA: when lowering type unsafe accesses to

large integers, the first inserted value would always create
an 'or X, 0'.  Even though this is trivially zapped by
instcombine, don't bother creating this pointless instruction.

llvm-svn: 106979

1 files changed, 6 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/ScalarReplAggregates.cpp b/llvm/lib/Transforms/Scalar/ScalarReplAggregates.cpp
index eefcbb44dbc..cae21e95fd5 100644
--- a/llvm/lib/Transforms/Scalar/ScalarReplAggregates.cpp
+++ b/llvm/lib/Transforms/Scalar/ScalarReplAggregates.cpp
@@ -1655,7 +1655,12 @@ void SROA::RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI,
       SrcField = BinaryOperator::CreateShl(SrcField, ShiftVal, "", LI);
     }
 
-    ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI);
+    // Don't create an 'or x, 0' on the first iteration.
+    if (!isa<Constant>(ResultVal) ||
+        !cast<Constant>(ResultVal)->isNullValue())
+      ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI);
+    else
+      ResultVal = SrcField;
   }
 
   // Handle tail padding by truncating the result