1 files changed, 20 insertions, 2 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index c63eb7f..4f548cb 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -1791,8 +1791,26 @@ SDValue SelectionDAGBuilder::getValueImpl(const Value *V) {
   if (const Constant *C = dyn_cast<Constant>(V)) {
     EVT VT = TLI.getValueType(DAG.getDataLayout(), V->getType(), true);
 
-    if (const ConstantInt *CI = dyn_cast<ConstantInt>(C))
-      return DAG.getConstant(*CI, getCurSDLoc(), VT);
+    if (const ConstantInt *CI = dyn_cast<ConstantInt>(C)) {
+      SDLoc DL = getCurSDLoc();
+
+      // DAG.getConstant() may attempt to legalise the vector constant which can
+      // significantly change the combines applied to the DAG. To reduce the
+      // divergence when enabling ConstantInt based vectors we try to construct
+      // the DAG in the same way as shufflevector based splats. TODO: The
+      // divergence sometimes leads to better optimisations. Ideally we should
+      // prevent DAG.getConstant() from legalising too early but there are some
+      // degradations preventing this.
+      if (VT.isScalableVector())
+        return DAG.getNode(
+            ISD::SPLAT_VECTOR, DL, VT,
+            DAG.getConstant(CI->getValue(), DL, VT.getVectorElementType()));
+      if (VT.isFixedLengthVector())
+        return DAG.getSplatBuildVector(
+            VT, DL,
+            DAG.getConstant(CI->getValue(), DL, VT.getVectorElementType()));
+      return DAG.getConstant(*CI, DL, VT);
+    }
 
     if (const GlobalValue *GV = dyn_cast<GlobalValue>(C))
       return DAG.getGlobalAddress(GV, getCurSDLoc(), VT);