Index: llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -247,6 +247,11 @@
     Res = NPN;
     break;
   }
+  case Instruction::FPToUI:
+  case Instruction::FPToSI:
+    Res = CastInst::Create(
+      static_cast<Instruction::CastOps>(Opc), I->getOperand(0), Ty);
+    break;
   default:
     // TODO: Can handle more cases here.
     llvm_unreachable("Unreachable!");
@@ -491,6 +496,16 @@
         return false;
     return true;
   }
+  case Instruction::FPToUI:
+  case Instruction::FPToSI: {
+    int32_t BitWidth = Ty->getScalarSizeInBits();
+    Type *InputTy = I->getOperand(0)->getType()->getScalarType();
+    const fltSemantics &semantics = InputTy->getFltSemantics();
+    int32_t MinBitWidth = I->getOpcode() == Instruction::FPToSI
+                        ? APFloatBase::semanticsMaxExponent(semantics) + 1
+                        : APFloatBase::semanticsMaxExponent(semantics);
+    return BitWidth > MinBitWidth;
+  }
   default:
     // TODO: Can handle more cases here.
     break;
Index: llvm/test/Transforms/InstCombine/trunc-fp-to-int.ll
===================================================================
--- llvm/test/Transforms/InstCombine/trunc-fp-to-int.ll
+++ llvm/test/Transforms/InstCombine/trunc-fp-to-int.ll
@@ -7,9 +7,8 @@
 
 define i16 @half_fptoui_i17_i16(half %x) {
 ; CHECK-LABEL: @half_fptoui_i17_i16(
-; CHECK-NEXT:    [[I:%.*]] = fptoui half [[X:%.*]] to i17
-; CHECK-NEXT:    [[R:%.*]] = trunc i17 [[I]] to i16
-; CHECK-NEXT:    ret i16 [[R]]
+; CHECK-NEXT:    [[I:%.*]] = fptoui half [[X:%.*]] to i16
+; CHECK-NEXT:    ret i16 [[I]]
 ;
   %i = fptoui half %x to i17
   %r = trunc i17 %i to i16
@@ -33,9 +32,8 @@
 
 define i16 @half_fptoui_i32_i16(half %x) {
 ; CHECK-LABEL: @half_fptoui_i32_i16(
-; CHECK-NEXT:    [[I:%.*]] = fptoui half [[X:%.*]] to i32
-; CHECK-NEXT:    [[R:%.*]] = trunc i32 [[I]] to i16
-; CHECK-NEXT:    ret i16 [[R]]
+; CHECK-NEXT:    [[I:%.*]] = fptoui half [[X:%.*]] to i16
+; CHECK-NEXT:    ret i16 [[I]]
 ;
   %i = fptoui half %x to i32
   %r = trunc i32 %i to i16
@@ -59,9 +57,8 @@
 
 define <4 x i16> @half_fptoui_4xi32_4xi16(<4 x half> %x) {
 ; CHECK-LABEL: @half_fptoui_4xi32_4xi16(
-; CHECK-NEXT:    [[I:%.*]] = fptoui <4 x half> [[X:%.*]] to <4 x i32>
-; CHECK-NEXT:    [[R:%.*]] = trunc <4 x i32> [[I]] to <4 x i16>
-; CHECK-NEXT:    ret <4 x i16> [[R]]
+; CHECK-NEXT:    [[I:%.*]] = fptoui <4 x half> [[X:%.*]] to <4 x i16>
+; CHECK-NEXT:    ret <4 x i16> [[I]]
 ;
   %i = fptoui <4 x half> %x to <4 x i32>
   %r = trunc <4 x i32> %i to <4 x i16>
@@ -70,9 +67,8 @@
 
 define i128 @bfloat_fptoui_i129_i128(bfloat %x) {
 ; CHECK-LABEL: @bfloat_fptoui_i129_i128(
-; CHECK-NEXT:    [[I:%.*]] = fptoui bfloat [[X:%.*]] to i129
-; CHECK-NEXT:    [[R:%.*]] = trunc i129 [[I]] to i128
-; CHECK-NEXT:    ret i128 [[R]]
+; CHECK-NEXT:    [[I:%.*]] = fptoui bfloat [[X:%.*]] to i128
+; CHECK-NEXT:    ret i128 [[I]]
 ;
   %i = fptoui bfloat %x to i129
   %r = trunc i129 %i to i128
@@ -94,9 +90,8 @@
 
 define i128 @float_fptoui_i129_i128(float %x) {
 ; CHECK-LABEL: @float_fptoui_i129_i128(
-; CHECK-NEXT:    [[I:%.*]] = fptoui float [[X:%.*]] to i129
-; CHECK-NEXT:    [[R:%.*]] = trunc i129 [[I]] to i128
-; CHECK-NEXT:    ret i128 [[R]]
+; CHECK-NEXT:    [[I:%.*]] = fptoui float [[X:%.*]] to i128
+; CHECK-NEXT:    ret i128 [[I]]
 ;
   %i = fptoui float %x to i129
   %r = trunc i129 %i to i128
@@ -116,11 +111,10 @@
   ret i127 %r
 }
 
-define i1024 @float_fptoui_i1025_i1024(double %x) {
-; CHECK-LABEL: @float_fptoui_i1025_i1024(
-; CHECK-NEXT:    [[I:%.*]] = fptoui double [[X:%.*]] to i1025
-; CHECK-NEXT:    [[R:%.*]] = trunc i1025 [[I]] to i1024
-; CHECK-NEXT:    ret i1024 [[R]]
+define i1024 @double_fptoui_i1025_i1024(double %x) {
+; CHECK-LABEL: @double_fptoui_i1025_i1024(
+; CHECK-NEXT:    [[I:%.*]] = fptoui double [[X:%.*]] to i1024
+; CHECK-NEXT:    ret i1024 [[I]]
 ;
   %i = fptoui double %x to i1025
   %r = trunc i1025 %i to i1024
@@ -129,13 +123,142 @@
 
 ; Negative test - not enough bits to hold max double value (2**1023 * (2 − 2**−52))
 
-define i1023 @float_fptoui_i1024_i1023(float %x) {
-; CHECK-LABEL: @float_fptoui_i1024_i1023(
-; CHECK-NEXT:    [[I:%.*]] = fptoui float [[X:%.*]] to i1024
+define i1023 @double_fptoui_i1024_i1023(double %x) {
+; CHECK-LABEL: @double_fptoui_i1024_i1023(
+; CHECK-NEXT:    [[I:%.*]] = fptoui double [[X:%.*]] to i1024
 ; CHECK-NEXT:    [[R:%.*]] = trunc i1024 [[I]] to i1023
 ; CHECK-NEXT:    ret i1023 [[R]]
 ;
-  %i = fptoui float %x to i1024
+  %i = fptoui double %x to i1024
   %r = trunc i1024 %i to i1023
   ret i1023 %r
 }
+
+; Negative test - not enough bits to hold min half value (-65504).
+
+define i16 @half_fptosi_i17_i16(half %x) {
+; CHECK-LABEL: @half_fptosi_i17_i16(
+; CHECK-NEXT:    [[I:%.*]] = fptosi half [[X:%.*]] to i17
+; CHECK-NEXT:    [[R:%.*]] = trunc i17 [[I]] to i16
+; CHECK-NEXT:    ret i16 [[R]]
+;
+  %i = fptosi half %x to i17
+  %r = trunc i17 %i to i16
+  ret i16 %r
+}
+
+define i17 @half_fptosi_i18_i17(half %x) {
+; CHECK-LABEL: @half_fptosi_i18_i17(
+; CHECK-NEXT:    [[I:%.*]] = fptosi half [[X:%.*]] to i17
+; CHECK-NEXT:    ret i17 [[I]]
+;
+  %i = fptosi half %x to i18
+  %r = trunc i18 %i to i17
+  ret i17 %r
+}
+
+; Wider intermediate type is ok.
+
+define i17 @half_fptosi_i32_i17(half %x) {
+; CHECK-LABEL: @half_fptosi_i32_i17(
+; CHECK-NEXT:    [[I:%.*]] = fptoui half [[X:%.*]] to i32
+; CHECK-NEXT:    [[R:%.*]] = trunc i32 [[I]] to i17
+; CHECK-NEXT:    ret i17 [[R]]
+;
+  %i = fptoui half %x to i32
+  %r = trunc i32 %i to i17
+  ret i17 %r
+}
+
+; Wider final type is ok.
+
+define i18 @half_fptoui_i32_i18(half %x) {
+; CHECK-LABEL: @half_fptoui_i32_i18(
+; CHECK-NEXT:    [[I:%.*]] = fptosi half [[X:%.*]] to i32
+; CHECK-NEXT:    [[R:%.*]] = trunc i32 [[I]] to i18
+; CHECK-NEXT:    ret i18 [[R]]
+;
+  %i = fptosi half %x to i32
+  %r = trunc i32 %i to i18
+  ret i18 %r
+}
+
+; Vectors work too.
+
+define <4 x i17> @half_fptosi_4xi32_4xi17(<4 x half> %x) {
+; CHECK-LABEL: @half_fptosi_4xi32_4xi17(
+; CHECK-NEXT:    [[I:%.*]] = fptosi <4 x half> [[X:%.*]] to <4 x i17>
+; CHECK-NEXT:    ret <4 x i17> [[I]]
+;
+  %i = fptosi <4 x half> %x to <4 x i32>
+  %r = trunc <4 x i32> %i to <4 x i17>
+  ret <4 x i17> %r
+}
+
+; Negative test - not enough bits to hold min float value.
+
+define i128 @bfloat_fptosi_i129_i128(bfloat %x) {
+; CHECK-LABEL: @bfloat_fptosi_i129_i128(
+; CHECK-NEXT:    [[I:%.*]] = fptosi bfloat [[X:%.*]] to i129
+; CHECK-NEXT:    [[R:%.*]] = trunc i129 [[I]] to i128
+; CHECK-NEXT:    ret i128 [[R]]
+;
+  %i = fptosi bfloat %x to i129
+  %r = trunc i129 %i to i128
+  ret i128 %r
+}
+
+define i129 @bfloat_fptosi_i130_i129(bfloat %x) {
+; CHECK-LABEL: @bfloat_fptosi_i130_i129(
+; CHECK-NEXT:    [[I:%.*]] = fptosi bfloat [[X:%.*]] to i129
+; CHECK-NEXT:    ret i129 [[I]]
+;
+  %i = fptosi bfloat %x to i130
+  %r = trunc i130 %i to i129
+  ret i129 %r
+}
+
+define i129 @float_fptosi_i130_i129(float %x) {
+; CHECK-LABEL: @float_fptosi_i130_i129(
+; CHECK-NEXT:    [[I:%.*]] = fptosi float [[X:%.*]] to i129
+; CHECK-NEXT:    ret i129 [[I]]
+;
+  %i = fptosi float %x to i130
+  %r = trunc i130 %i to i129
+  ret i129 %r
+}
+
+; Negative test - not enough bits to hold min float value.
+
+define i128 @float_fptosi_i129_i128(float %x) {
+; CHECK-LABEL: @float_fptosi_i129_i128(
+; CHECK-NEXT:    [[I:%.*]] = fptoui float [[X:%.*]] to i128
+; CHECK-NEXT:    ret i128 [[I]]
+;
+  %i = fptoui float %x to i129
+  %r = trunc i129 %i to i128
+  ret i128 %r
+}
+
+define i1025 @double_fptosi_i1026_i1025(double %x) {
+; CHECK-LABEL: @double_fptosi_i1026_i1025(
+; CHECK-NEXT:    [[I:%.*]] = fptosi double [[X:%.*]] to i1025
+; CHECK-NEXT:    ret i1025 [[I]]
+;
+  %i = fptosi double %x to i1026
+  %r = trunc i1026 %i to i1025
+  ret i1025 %r
+}
+
+; Negative test - not enough bits to hold min double value.
+
+define i1024 @double_fptosi_i1025_i1024(double %x) {
+; CHECK-LABEL: @double_fptosi_i1025_i1024(
+; CHECK-NEXT:    [[I:%.*]] = fptosi double [[X:%.*]] to i1025
+; CHECK-NEXT:    [[R:%.*]] = trunc i1025 [[I]] to i1024
+; CHECK-NEXT:    ret i1024 [[R]]
+;
+  %i = fptosi double %x to i1025
+  %r = trunc i1025 %i to i1024
+  ret i1024 %r
+}