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 +496,18 @@
         return false;
     return true;
   }
+  case Instruction::FPToUI:
+  case Instruction::FPToSI:
+    if (isGuaranteedNotToBeUndefOrPoison(I->getOperand(0))) {
+      if (I->getOperand(0)->getType()->getScalarType()->isHalfTy()) {
+        // TODO: For FPToSI, the minimum trunc type is i17 but we only handle
+        // simple types while evaluating truncations.
+        uint32_t MinBitWidth = I->getOpcode() == Instruction::FPToUI 
+                             ? 16 : 32;
+        return Ty->getScalarSizeInBits() >= MinBitWidth;
+      }
+    }
+    break;
   default:
     // TODO: Can handle more cases here.
     break;
Index: llvm/test/Transforms/InstCombine/trunc-fp-to-int.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/InstCombine/trunc-fp-to-int.ll
@@ -0,0 +1,152 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=instcombine -S -o - %s | FileCheck %s
+
+define i15 @half_fptoui_i32_i15_noundef(half noundef %x) {
+; CHECK-LABEL: @half_fptoui_i32_i15_noundef(
+; CHECK-NEXT:    [[CONV:%.*]] = fptoui half [[X:%.*]] to i32
+; CHECK-NEXT:    [[CONV_1:%.*]] = trunc i32 [[CONV]] to i15
+; CHECK-NEXT:    ret i15 [[CONV_1]]
+;
+  %conv = fptoui half %x to i32
+  %conv.1 = trunc i32 %conv to i15
+  ret i15 %conv.1
+}
+
+define i16 @half_fptoui_i32_i16_noundef(half noundef %x) {
+; CHECK-LABEL: @half_fptoui_i32_i16_noundef(
+; CHECK-NEXT:    [[CONV:%.*]] = fptoui half [[X:%.*]] to i16
+; CHECK-NEXT:    ret i16 [[CONV]]
+;
+  %conv = fptoui half %x to i32
+  %conv.1 = trunc i32 %conv to i16
+  ret i16 %conv.1
+}
+
+define <4 x i16> @half_fptoui_4xi32_4xi16_noundef(<4 x half> noundef %x) {
+; CHECK-LABEL: @half_fptoui_4xi32_4xi16_noundef(
+; CHECK-NEXT:    [[CONV:%.*]] = fptoui <4 x half> [[X:%.*]] to <4 x i16>
+; CHECK-NEXT:    ret <4 x i16> [[CONV]]
+;
+  %conv = fptoui <4 x half> %x to <4 x i32>
+  %conv.1 = trunc <4 x i32> %conv to <4 x i16>
+  ret <4 x i16> %conv.1
+}
+
+define i16 @half_fptoui_i32_i16(half %x) {
+; CHECK-LABEL: @half_fptoui_i32_i16(
+; CHECK-NEXT:    [[CONV:%.*]] = fptoui half [[X:%.*]] to i32
+; CHECK-NEXT:    [[CONV_1:%.*]] = trunc i32 [[CONV]] to i16
+; CHECK-NEXT:    ret i16 [[CONV_1]]
+;
+  %conv = fptoui half %x to i32
+  %conv.1 = trunc i32 %conv to i16
+  ret i16 %conv.1
+}
+
+define i16 @half_fptosi_i32_i16_noundef(half noundef %x) {
+; CHECK-LABEL: @half_fptosi_i32_i16_noundef(
+; CHECK-NEXT:    [[CONV:%.*]] = fptosi half [[X:%.*]] to i32
+; CHECK-NEXT:    [[CONV_1:%.*]] = trunc i32 [[CONV]] to i16
+; CHECK-NEXT:    ret i16 [[CONV_1]]
+;
+  %conv = fptosi half %x to i32
+  %conv.1 = trunc i32 %conv to i16
+  ret i16 %conv.1
+}
+
+define i17 @half_fptosi_i32_i17_noundef(half noundef %x) {
+; CHECK-LABEL: @half_fptosi_i32_i17_noundef(
+; CHECK-NEXT:    [[CONV:%.*]] = fptosi half [[X:%.*]] to i32
+; CHECK-NEXT:    [[CONV_1:%.*]] = trunc i32 [[CONV]] to i17
+; CHECK-NEXT:    ret i17 [[CONV_1]]
+;
+  %conv = fptosi half %x to i32
+  %conv.1 = trunc i32 %conv to i17
+  ret i17 %conv.1
+}
+
+define i17 @half_fptosi_i32_i17(half %x) {
+; CHECK-LABEL: @half_fptosi_i32_i17(
+; CHECK-NEXT:    [[CONV:%.*]] = fptosi half [[X:%.*]] to i32
+; CHECK-NEXT:    [[CONV_1:%.*]] = trunc i32 [[CONV]] to i17
+; CHECK-NEXT:    ret i17 [[CONV_1]]
+;
+  %conv = fptosi half %x to i32
+  %conv.1 = trunc i32 %conv to i17
+  ret i17 %conv.1
+}
+
+define i32 @half_fptosi_i64_i32_noundef(half noundef %x) {
+; CHECK-LABEL: @half_fptosi_i64_i32_noundef(
+; CHECK-NEXT:    [[CONV:%.*]] = fptosi half [[X:%.*]] to i32
+; CHECK-NEXT:    ret i32 [[CONV]]
+;
+  %conv = fptosi half %x to i64
+  %conv.1 = trunc i64 %conv to i32
+  ret i32 %conv.1
+}
+
+define <4 x i32> @half_fptosi_4xi64_4xi32_noundef(<4 x half> noundef %x) {
+; CHECK-LABEL: @half_fptosi_4xi64_4xi32_noundef(
+; CHECK-NEXT:    [[CONV:%.*]] = fptoui <4 x half> [[X:%.*]] to <4 x i32>
+; CHECK-NEXT:    ret <4 x i32> [[CONV]]
+;
+  %conv = fptoui <4 x half> %x to <4 x i64>
+  %conv.1 = trunc <4 x i64> %conv to <4 x i32>
+  ret <4 x i32> %conv.1
+}
+
+define i32 @half_fptosi_i64_i32(half %x) {
+; CHECK-LABEL: @half_fptosi_i64_i32(
+; CHECK-NEXT:    [[CONV:%.*]] = fptosi half [[X:%.*]] to i64
+; CHECK-NEXT:    [[CONV_1:%.*]] = trunc i64 [[CONV]] to i32
+; CHECK-NEXT:    ret i32 [[CONV_1]]
+;
+  %conv = fptosi half %x to i64
+  %conv.1 = trunc i64 %conv to i32
+  ret i32 %conv.1
+}
+
+define i32 @float_fptoui_i64_i32_noundef(float noundef %x) {
+; CHECK-LABEL: @float_fptoui_i64_i32_noundef(
+; CHECK-NEXT:    [[CONV:%.*]] = fptoui float [[X:%.*]] to i64
+; CHECK-NEXT:    [[CONV_1:%.*]] = trunc i64 [[CONV]] to i32
+; CHECK-NEXT:    ret i32 [[CONV_1]]
+;
+  %conv = fptoui float %x to i64
+  %conv.1 = trunc i64 %conv to i32
+  ret i32 %conv.1
+}
+
+define i32 @float_fptosi_i64_i32_noundef(float noundef %x) {
+; CHECK-LABEL: @float_fptosi_i64_i32_noundef(
+; CHECK-NEXT:    [[CONV:%.*]] = fptosi float [[X:%.*]] to i64
+; CHECK-NEXT:    [[CONV_1:%.*]] = trunc i64 [[CONV]] to i32
+; CHECK-NEXT:    ret i32 [[CONV_1]]
+;
+  %conv = fptosi float %x to i64
+  %conv.1 = trunc i64 %conv to i32
+  ret i32 %conv.1
+}
+
+define i64 @float_fptoui_i128_i64_noundef(float noundef %x) {
+; CHECK-LABEL: @float_fptoui_i128_i64_noundef(
+; CHECK-NEXT:    [[CONV:%.*]] = fptoui float [[X:%.*]] to i128
+; CHECK-NEXT:    [[CONV_1:%.*]] = trunc i128 [[CONV]] to i64
+; CHECK-NEXT:    ret i64 [[CONV_1]]
+;
+  %conv = fptoui float %x to i128
+  %conv.1 = trunc i128 %conv to i64
+  ret i64 %conv.1
+}
+
+define i64 @float_fptosi_i128_i64_noundef(float noundef %x) {
+; CHECK-LABEL: @float_fptosi_i128_i64_noundef(
+; CHECK-NEXT:    [[CONV:%.*]] = fptosi float [[X:%.*]] to i128
+; CHECK-NEXT:    [[CONV_1:%.*]] = trunc i128 [[CONV]] to i64
+; CHECK-NEXT:    ret i64 [[CONV_1]]
+;
+  %conv = fptosi float %x to i128
+  %conv.1 = trunc i128 %conv to i64
+  ret i64 %conv.1
+}