Index: lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -259,19 +259,25 @@
                            (VT == MVT::f64) ? MVT::i64 : MVT::i32);
   }
 
+  APFloat APF = CFP->getValueAPF();
   EVT OrigVT = VT;
   EVT SVT = VT;
-  while (SVT != MVT::f32 && SVT != MVT::f16) {
-    SVT = (MVT::SimpleValueType)(SVT.getSimpleVT().SimpleTy - 1);
-    if (ConstantFPSDNode::isValueValidForType(SVT, CFP->getValueAPF()) &&
-        // Only do this if the target has a native EXTLOAD instruction from
-        // smaller type.
-        TLI.isLoadExtLegal(ISD::EXTLOAD, OrigVT, SVT) &&
-        TLI.ShouldShrinkFPConstant(OrigVT)) {
-      Type *SType = SVT.getTypeForEVT(*DAG.getContext());
-      LLVMC = cast<ConstantFP>(ConstantExpr::getFPTrunc(LLVMC, SType));
-      VT = SVT;
-      Extend = true;
+
+  // We don't want to shrink SNaNs. Converting the SNaN back to its real type
+  // can cause it to be changed into a QNaN on some platforms (e.g. on SystemZ).
+  if (!APF.isSignaling()) {
+    while (SVT != MVT::f32 && SVT != MVT::f16) {
+      SVT = (MVT::SimpleValueType)(SVT.getSimpleVT().SimpleTy - 1);
+      if (ConstantFPSDNode::isValueValidForType(SVT, APF) &&
+          // Only do this if the target has a native EXTLOAD instruction from
+          // smaller type.
+          TLI.isLoadExtLegal(ISD::EXTLOAD, OrigVT, SVT) &&
+          TLI.ShouldShrinkFPConstant(OrigVT)) {
+        Type *SType = SVT.getTypeForEVT(*DAG.getContext());
+        LLVMC = cast<ConstantFP>(ConstantExpr::getFPTrunc(LLVMC, SType));
+        VT = SVT;
+        Extend = true;
+      }
     }
   }
 
Index: test/CodeGen/SystemZ/fp-const-10.ll
===================================================================
--- test/CodeGen/SystemZ/fp-const-10.ll
+++ test/CodeGen/SystemZ/fp-const-10.ll
@@ -0,0 +1,15 @@
+; Test loads of SNaN.
+;
+; RUN: llc < %s -mtriple=s390x-linux-gnu | FileCheck %s
+
+; Test that we don't do an FP extending load, as this would result in a
+; converstion to QNaN.
+define double @f1() {
+; CHECK-LABEL: .LCPI0_0
+; CHECK:      .quad   9219994337134247936
+; CHECK-LABEL: f1:
+; CHECK:      larl    %r1, .LCPI0_0
+; CHECK-NOT:  ldeb    %f0, 0(%r1)
+; CHECK:      ld      %f0, 0(%r1)
+  ret double 0x7FF4000000000000
+}