Index: llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1615,13 +1615,19 @@
         return CastInst::CreateFPCast(ExactResult, Ty);
       }
     }
+  }
 
-    // (fptrunc (fneg x)) -> (fneg (fptrunc x))
-    Value *X;
-    if (match(OpI, m_FNeg(m_Value(X)))) {
-      Value *InnerTrunc = Builder.CreateFPTrunc(X, Ty);
-      return BinaryOperator::CreateFNegFMF(InnerTrunc, OpI);
-    }
+  // (fptrunc (fneg x)) -> (fneg (fptrunc x))
+  Value *X;
+  Value *Op = FPT.getOperand(0);
+  if (match(Op, m_FNeg(m_Value(X)))) {
+    Value *InnerTrunc = Builder.CreateFPTrunc(X, Ty);
+
+    // FIXME: Once we're sure that unary FNeg optimizations are on par with
+    // binary FNeg, this should always return a unary operator. 
+    if (isa<BinaryOperator>(Op)
+      return BinaryOperator::CreateFNegFMF(InnerTrunc, cast<Instruction>(Op));
+    return UnaryOperator::CreateFNegFMF(InnerTrunc, cast<Instruction>(Op));
   }
 
   if (auto *II = dyn_cast<IntrinsicInst>(FPT.getOperand(0))) {
Index: llvm/test/Transforms/InstCombine/fpcast.ll
===================================================================
--- llvm/test/Transforms/InstCombine/fpcast.ll
+++ llvm/test/Transforms/InstCombine/fpcast.ll
@@ -40,11 +40,10 @@
   ret half %c
 }
 
-; FIXME: This combine isn't working.
 define half @unary_fneg_fptrunc(float %a) {
 ; CHECK-LABEL: @unary_fneg_fptrunc(
-; CHECK-NEXT:    [[B:%.*]] = fneg float [[A:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = fptrunc float [[B]] to half
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc float [[A:%.*]] to half
+; CHECK-NEXT:    [[C:%.*]] = fsub half 0xH8000, [[TMP1]]
 ; CHECK-NEXT:    ret half [[C]]
 ;
   %b = fneg float %a
@@ -63,11 +62,10 @@
   ret <2 x half> %c
 }
 
-; FIXME: This combine isn't working.
 define <2 x half> @unary_fneg_fptrunc_vec(<2 x float> %a) {
 ; CHECK-LABEL: @unary_fneg_fptrunc_vec(
-; CHECK-NEXT:    [[B:%.*]] = fneg <2 x float> [[A:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = fptrunc <2 x float> [[B]] to <2 x half>
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc <2 x float> [[A:%.*]] to <2 x half>
+; CHECK-NEXT:    [[C:%.*]] = fsub <2 x half> <half 0xH8000, half 0xH8000>, [[TMP1]]
 ; CHECK-NEXT:    ret <2 x half> [[C]]
 ;
   %b = fneg <2 x float> %a
@@ -86,11 +84,10 @@
   ret half %c
 }
 
-; FIXME: This combine isn't working.
 define half @test4_unary_fneg-fast(float %a) {
 ; CHECK-LABEL: @test4_unary_fneg-fast(
-; CHECK-NEXT:    [[B:%.*]] = fneg fast float [[A:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = fptrunc float [[B]] to half
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc float [[A:%.*]] to half
+; CHECK-NEXT:    [[C:%.*]] = fsub fast half 0xH8000, [[TMP1]]
 ; CHECK-NEXT:    ret half [[C]]
 ;
   %b = fneg fast float %a
Index: llvm/test/Transforms/InstCombine/fpextend.ll
===================================================================
--- llvm/test/Transforms/InstCombine/fpextend.ll
+++ llvm/test/Transforms/InstCombine/fpextend.ll
@@ -55,13 +55,10 @@
   ret float %tmp34
 }
 
-; FIXME: This combine isn't working.
 define float @test4_unary_fneg(float %x) nounwind  {
 ; CHECK-LABEL: @test4_unary_fneg(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP1:%.*]] = fpext float [[X:%.*]] to double
-; CHECK-NEXT:    [[TMP2:%.*]] = fneg double [[TMP1]]
-; CHECK-NEXT:    [[TMP34:%.*]] = fptrunc double [[TMP2]] to float
+; CHECK-NEXT:    [[TMP34:%.*]] = fsub float -0.000000e+00, [[X:%.*]]
 ; CHECK-NEXT:    ret float [[TMP34]]
 ;
 entry:
Index: llvm/test/Transforms/InstCombine/fsub.ll
===================================================================
--- llvm/test/Transforms/InstCombine/fsub.ll
+++ llvm/test/Transforms/InstCombine/fsub.ll
@@ -334,12 +334,11 @@
   ret float %t3
 }
 
-; FIXME: This combine isn't working.
 define float @unary_neg_trunc_op1_extra_use(double %a, float %b) {
 ; CHECK-LABEL: @unary_neg_trunc_op1_extra_use(
-; CHECK-NEXT:    [[T1:%.*]] = fneg double [[A:%.*]]
-; CHECK-NEXT:    [[T2:%.*]] = fptrunc double [[T1]] to float
-; CHECK-NEXT:    [[T3:%.*]] = fsub float [[B:%.*]], [[T2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc double [[A:%.*]] to float
+; CHECK-NEXT:    [[T2:%.*]] = fsub float -0.000000e+00, [[TMP1]]
+; CHECK-NEXT:    [[T3:%.*]] = fadd float [[TMP1]], [[B:%.*]]
 ; CHECK-NEXT:    call void @use(float [[T2]])
 ; CHECK-NEXT:    ret float [[T3]]
 ;
@@ -355,8 +354,9 @@
 define float @neg_trunc_op1_extra_uses(double %a, float %b) {
 ; CHECK-LABEL: @neg_trunc_op1_extra_uses(
 ; CHECK-NEXT:    [[T1:%.*]] = fsub double -0.000000e+00, [[A:%.*]]
-; CHECK-NEXT:    [[T2:%.*]] = fptrunc double [[T1]] to float
-; CHECK-NEXT:    [[T3:%.*]] = fsub float [[B:%.*]], [[T2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc double [[A]] to float
+; CHECK-NEXT:    [[T2:%.*]] = fsub float -0.000000e+00, [[TMP1]]
+; CHECK-NEXT:    [[T3:%.*]] = fadd float [[TMP1]], [[B:%.*]]
 ; CHECK-NEXT:    call void @use2(float [[T2]], double [[T1]])
 ; CHECK-NEXT:    ret float [[T3]]
 ;
@@ -370,8 +370,9 @@
 define float @unary_neg_trunc_op1_extra_uses(double %a, float %b) {
 ; CHECK-LABEL: @unary_neg_trunc_op1_extra_uses(
 ; CHECK-NEXT:    [[T1:%.*]] = fneg double [[A:%.*]]
-; CHECK-NEXT:    [[T2:%.*]] = fptrunc double [[T1]] to float
-; CHECK-NEXT:    [[T3:%.*]] = fsub float [[B:%.*]], [[T2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc double [[A]] to float
+; CHECK-NEXT:    [[T2:%.*]] = fsub float -0.000000e+00, [[TMP1]]
+; CHECK-NEXT:    [[T3:%.*]] = fadd float [[TMP1]], [[B:%.*]]
 ; CHECK-NEXT:    call void @use2(float [[T2]], double [[T1]])
 ; CHECK-NEXT:    ret float [[T3]]
 ;