[CodeGen] Flip lanes when lowering __builtin_palignr with one lane

Otherwise we'd pick the wrong lane for the resulting shuffle and
miscompile code. PR24187.

llvm-svn: 242678

1 files changed, 1 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index 9e538703177..463b3eee3d3 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -6238,6 +6238,7 @@ Value *CodeGenFunction::EmitX86BuiltinExpr(unsigned BuiltinID,
     // but less than two lanes, convert to shifting in zeroes.
     if (ShiftVal > NumLaneElts) {
       ShiftVal -= NumLaneElts;
+      Ops[1] = Ops[0];
       Ops[0] = llvm::Constant::getNullValue(Ops[0]->getType());
     }