Index: lib/Transforms/InstCombine/InstCombineCasts.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1420,6 +1420,42 @@
   return nullptr;
 }
 
+static Constant *shrinkFPConstant(ConstantFP *CFP) {
+  if (CFP->getType() == Type::getPPC_FP128Ty(CFP->getContext()))
+    return nullptr;  // No constant folding of this.
+  // See if the value can be truncated to half and then reextended.
+  if (Constant *NewCFP = fitsInFPType(CFP, APFloat::IEEEhalf()))
+    return NewCFP;
+  // See if the value can be truncated to float and then reextended.
+  if (Constant *NewCFP = fitsInFPType(CFP, APFloat::IEEEsingle()))
+    return NewCFP;
+  if (CFP->getType()->isDoubleTy())
+    return nullptr;  // Won't shrink.
+  if (Constant *NewCFP = fitsInFPType(CFP, APFloat::IEEEdouble()))
+    return NewCFP;
+  // Don't try to shrink to various long double types.
+  return nullptr;
+}
+
+static Constant *shrinkFPConstantVector(Constant *CV) {
+  SmallVector<Constant *, 8> Ops;
+
+  unsigned NumElts = CV->getType()->getVectorNumElements();
+  for (unsigned i = 0; i != NumElts; ++i) {
+    auto *CFP = dyn_cast_or_null<ConstantFP>(CV->getAggregateElement(i));
+    if (!CFP)
+      return nullptr;
+    Constant *NewCFP = shrinkFPConstant(CFP);
+    if (!NewCFP)
+      return nullptr;
+    // This was a shrinkable constant, save it.
+    Ops.push_back(NewCFP);
+  }
+  // We were able to shrink all elements of the vector, create a new vector
+  // with the smaller constants.
+  return ConstantVector::get(Ops);
+}
+
 /// Look through floating-point extensions until we get the source value.
 static Value *lookThroughFPExtensions(Value *V) {
   while (auto *FPExt = dyn_cast<FPExtInst>(V))
@@ -1428,21 +1464,15 @@
   // If this value is a constant, return the constant in the smallest FP type
   // that can accurately represent it.  This allows us to turn
   // (float)((double)X+2.0) into x+2.0f.
-  if (auto *CFP = dyn_cast<ConstantFP>(V)) {
-    if (CFP->getType() == Type::getPPC_FP128Ty(V->getContext()))
-      return V;  // No constant folding of this.
-    // See if the value can be truncated to half and then reextended.
-    if (Value *V = fitsInFPType(CFP, APFloat::IEEEhalf()))
-      return V;
-    // See if the value can be truncated to float and then reextended.
-    if (Value *V = fitsInFPType(CFP, APFloat::IEEEsingle()))
-      return V;
-    if (CFP->getType()->isDoubleTy())
-      return V;  // Won't shrink.
-    if (Value *V = fitsInFPType(CFP, APFloat::IEEEdouble()))
-      return V;
-    // Don't try to shrink to various long double types.
-  }
+  if (auto *CFP = dyn_cast<ConstantFP>(V))
+    if (Constant *NewCFP = shrinkFPConstant(CFP))
+      return NewCFP;
+
+  // Try to do the same for vectors of FP constants.
+  if (auto *CV = dyn_cast<Constant>(V))
+    if (CV->getType()->isVectorTy())
+      if (Constant *NewCV = shrinkFPConstantVector(CV))
+        return NewCV;
 
   return V;
 }
Index: test/Transforms/InstCombine/fpextend.ll
===================================================================
--- test/Transforms/InstCombine/fpextend.ll
+++ test/Transforms/InstCombine/fpextend.ll
@@ -84,9 +84,7 @@
 ; CHECK-LABEL: @test5(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[TMP:%.*]] = load <2 x float>, <2 x float>* @Z, align 8
-; CHECK-NEXT:    [[TMP1:%.*]] = fpext <2 x float> [[TMP]] to <2 x double>
-; CHECK-NEXT:    [[TMP3:%.*]] = fadd <2 x double> [[TMP1]], zeroinitializer
-; CHECK-NEXT:    [[TMP34:%.*]] = fptrunc <2 x double> [[TMP3]] to <2 x float>
+; CHECK-NEXT:    [[TMP34:%.*]] = fadd <2 x float> [[TMP]], zeroinitializer
 ; CHECK-NEXT:    store <2 x float> [[TMP34]], <2 x float>* @Z, align 8
 ; CHECK-NEXT:    ret void
 ;
@@ -104,9 +102,7 @@
 ; CHECK-LABEL: @test6(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[TMP:%.*]] = load <2 x float>, <2 x float>* @Z, align 8
-; CHECK-NEXT:    [[TMP1:%.*]] = fpext <2 x float> [[TMP]] to <2 x double>
-; CHECK-NEXT:    [[TMP3:%.*]] = fadd <2 x double> [[TMP1]], <double 0.000000e+00, double -0.000000e+00>
-; CHECK-NEXT:    [[TMP34:%.*]] = fptrunc <2 x double> [[TMP3]] to <2 x float>
+; CHECK-NEXT:    [[TMP34:%.*]] = fadd <2 x float> [[TMP]], <float 0.000000e+00, float -0.000000e+00>
 ; CHECK-NEXT:    store <2 x float> [[TMP34]], <2 x float>* @Z, align 8
 ; CHECK-NEXT:    ret void
 ;