diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 7221c987b9821..62853ca0f72b0 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1847,15 +1847,16 @@ Instruction *InstCombinerImpl::visitFPTrunc(FPTruncInst &FPT) {
   Value *X;
   Instruction *Op = dyn_cast<Instruction>(FPT.getOperand(0));
   if (Op && Op->hasOneUse()) {
-    // FIXME: The FMF should propagate from the fptrunc, not the source op.
     IRBuilder<>::FastMathFlagGuard FMFG(Builder);
-    if (isa<FPMathOperator>(Op))
-      Builder.setFastMathFlags(Op->getFastMathFlags());
+    FastMathFlags FMF = FPT.getFastMathFlags();
+    if (auto *FPMO = dyn_cast<FPMathOperator>(Op))
+      FMF &= FPMO->getFastMathFlags();
+    Builder.setFastMathFlags(FMF);
 
     if (match(Op, m_FNeg(m_Value(X)))) {
       Value *InnerTrunc = Builder.CreateFPTrunc(X, Ty);
-
-      return UnaryOperator::CreateFNegFMF(InnerTrunc, Op);
+      Value *Neg = Builder.CreateFNeg(InnerTrunc);
+      return replaceInstUsesWith(FPT, Neg);
     }
 
     // If we are truncating a select that has an extended operand, we can
diff --git a/llvm/test/Transforms/InstCombine/fpcast.ll b/llvm/test/Transforms/InstCombine/fpcast.ll
index 029e513ceafbc..d5290b572aefd 100644
--- a/llvm/test/Transforms/InstCombine/fpcast.ll
+++ b/llvm/test/Transforms/InstCombine/fpcast.ll
@@ -29,6 +29,17 @@ define half @test3(float %a) {
   ret half %c
 }
 
+define half @test3_fast(float %a) {
+; CHECK-LABEL: @test3_fast(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc float [[A:%.*]] to half
+; CHECK-NEXT:    [[C:%.*]] = call half @llvm.fabs.f16(half [[TMP1]])
+; CHECK-NEXT:    ret half [[C]]
+;
+  %b = call float @llvm.fabs.f32(float %a)
+  %c = fptrunc fast float %b to half
+  ret half %c
+}
+
 define half @fneg_fptrunc(float %a) {
 ; CHECK-LABEL: @fneg_fptrunc(
 ; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc float [[A:%.*]] to half
@@ -78,6 +89,28 @@ define half @test4-fast(float %a) {
 ; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc fast float [[A:%.*]] to half
 ; CHECK-NEXT:    [[C:%.*]] = fneg fast half [[TMP1]]
 ; CHECK-NEXT:    ret half [[C]]
+;
+  %b = fsub fast float -0.0, %a
+  %c = fptrunc fast float %b to half
+  ret half %c
+}
+
+define half @test4-mixed-fast-1(float %a) {
+; CHECK-LABEL: @test4-mixed-fast-1(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc float [[A:%.*]] to half
+; CHECK-NEXT:    [[C:%.*]] = fneg half [[TMP1]]
+; CHECK-NEXT:    ret half [[C]]
+;
+  %b = fsub float -0.0, %a
+  %c = fptrunc fast float %b to half
+  ret half %c
+}
+
+define half @test4-mixed-fast-2(float %a) {
+; CHECK-LABEL: @test4-mixed-fast-2(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc float [[A:%.*]] to half
+; CHECK-NEXT:    [[C:%.*]] = fneg half [[TMP1]]
+; CHECK-NEXT:    ret half [[C]]
 ;
   %b = fsub fast float -0.0, %a
   %c = fptrunc float %b to half
@@ -89,12 +122,67 @@ define half @test4_unary_fneg-fast(float %a) {
 ; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc fast float [[A:%.*]] to half
 ; CHECK-NEXT:    [[C:%.*]] = fneg fast half [[TMP1]]
 ; CHECK-NEXT:    ret half [[C]]
+;
+  %b = fneg fast float %a
+  %c = fptrunc fast float %b to half
+  ret half %c
+}
+
+define half @test4_unary_fneg-mixed-fast-1(float %a) {
+; CHECK-LABEL: @test4_unary_fneg-mixed-fast-1(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc float [[A:%.*]] to half
+; CHECK-NEXT:    [[C:%.*]] = fneg half [[TMP1]]
+; CHECK-NEXT:    ret half [[C]]
+;
+  %b = fneg float %a
+  %c = fptrunc fast float %b to half
+  ret half %c
+}
+
+define half @test4_unary_fneg-mixed-fast-2(float %a) {
+; CHECK-LABEL: @test4_unary_fneg-mixed-fast-2(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc float [[A:%.*]] to half
+; CHECK-NEXT:    [[C:%.*]] = fneg half [[TMP1]]
+; CHECK-NEXT:    ret half [[C]]
 ;
   %b = fneg fast float %a
   %c = fptrunc float %b to half
   ret half %c
 }
 
+define <2 x half> @test4_unary_fneg-vec-fast(<2 x float> %a) {
+; CHECK-LABEL: @test4_unary_fneg-vec-fast(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc fast <2 x float> [[A:%.*]] to <2 x half>
+; CHECK-NEXT:    [[C:%.*]] = fneg fast <2 x half> [[TMP1]]
+; CHECK-NEXT:    ret <2 x half> [[C]]
+;
+  %b = fneg fast <2 x float> %a
+  %c = fptrunc fast <2 x float> %b to <2 x half>
+  ret <2 x half> %c
+}
+
+define <2 x half> @test4_unary_fneg-vec-mixed-fast-1(<2 x float> %a) {
+; CHECK-LABEL: @test4_unary_fneg-vec-mixed-fast-1(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc <2 x float> [[A:%.*]] to <2 x half>
+; CHECK-NEXT:    [[C:%.*]] = fneg <2 x half> [[TMP1]]
+; CHECK-NEXT:    ret <2 x half> [[C]]
+;
+  %b = fneg <2 x float> %a
+  %c = fptrunc fast <2 x float> %b to <2 x half>
+  ret <2 x half> %c
+}
+
+define <2 x half> @test4_unary_fneg-vec-mixed-fast-2(<2 x float> %a) {
+; CHECK-LABEL: @test4_unary_fneg-vec-mixed-fast-2(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc <2 x float> [[A:%.*]] to <2 x half>
+; CHECK-NEXT:    [[C:%.*]] = fneg <2 x half> [[TMP1]]
+; CHECK-NEXT:    ret <2 x half> [[C]]
+;
+  %b = fneg fast <2 x float> %a
+  %c = fptrunc <2 x float> %b to <2 x half>
+  ret <2 x half> %c
+}
+
 define half @test5(float %a, float %b, float %c) {
 ; CHECK-LABEL: @test5(
 ; CHECK-NEXT:    [[D:%.*]] = fcmp ogt float [[A:%.*]], [[B:%.*]]
diff --git a/llvm/test/Transforms/InstCombine/fptrunc.ll b/llvm/test/Transforms/InstCombine/fptrunc.ll
index a4296a326c4bc..0b5d8b3cd06e0 100644
--- a/llvm/test/Transforms/InstCombine/fptrunc.ll
+++ b/llvm/test/Transforms/InstCombine/fptrunc.ll
@@ -61,6 +61,18 @@ define float @fptrunc_select_true_val(float %x, double %y, i1 %cond) {
   ret float %r
 }
 
+define float @fptrunc_fast_select_true_val(float %x, double %y, i1 %cond) {
+; CHECK-LABEL: @fptrunc_fast_select_true_val(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc fast double [[Y:%.*]] to float
+; CHECK-NEXT:    [[NARROW_SEL:%.*]] = select i1 [[COND:%.*]], float [[TMP1]], float [[X:%.*]]
+; CHECK-NEXT:    ret float [[NARROW_SEL]]
+;
+  %e = fpext float %x to double
+  %sel = select fast i1 %cond, double %y, double %e
+  %r = fptrunc fast double %sel to float
+  ret float %r
+}
+
 define <2 x float> @fptrunc_select_false_val(<2 x float> %x, <2 x double> %y, <2 x i1> %cond) {
 ; CHECK-LABEL: @fptrunc_select_false_val(
 ; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc <2 x double> [[Y:%.*]] to <2 x float>
@@ -73,6 +85,18 @@ define <2 x float> @fptrunc_select_false_val(<2 x float> %x, <2 x double> %y, <2
   ret <2 x float> %r
 }
 
+define <2 x float> @fptrunc_nnan_select_false_val(<2 x float> %x, <2 x double> %y, <2 x i1> %cond) {
+; CHECK-LABEL: @fptrunc_nnan_select_false_val(
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc nnan <2 x double> [[Y:%.*]] to <2 x float>
+; CHECK-NEXT:    [[NARROW_SEL:%.*]] = select <2 x i1> [[COND:%.*]], <2 x float> [[X:%.*]], <2 x float> [[TMP1]]
+; CHECK-NEXT:    ret <2 x float> [[NARROW_SEL]]
+;
+  %e = fpext <2 x float> %x to <2 x double>
+  %sel = select nnan <2 x i1> %cond, <2 x double> %e, <2 x double> %y
+  %r = fptrunc nnan <2 x double> %sel to <2 x float>
+  ret <2 x float> %r
+}
+
 declare void @use(float)
 
 define half @fptrunc_select_true_val_extra_use(half %x, float %y, i1 %cond) {