Index: lib/Analysis/InstructionSimplify.cpp
===================================================================
--- lib/Analysis/InstructionSimplify.cpp
+++ lib/Analysis/InstructionSimplify.cpp
@@ -4701,6 +4701,17 @@
         match(Op0, m_Intrinsic<Intrinsic::pow>(m_SpecificFP(10.0),
                                                m_Value(X)))) return X;
     break;
+  case Intrinsic::floor:
+  case Intrinsic::trunc:
+  case Intrinsic::ceil:
+  case Intrinsic::round:
+  case Intrinsic::nearbyint:
+  case Intrinsic::rint: {
+    // floor (sitofp x) -> x
+    if (match(Op0, m_SIToFP(m_Value())))
+      return Op0;
+    break;
+  }
   default:
     break;
   }
Index: test/Transforms/InstSimplify/round-intrinsics.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstSimplify/round-intrinsics.ll
@@ -0,0 +1,115 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -instsimplify %s | FileCheck %s
+
+define float @sitofp_floor(i32 %arg) {
+; CHECK-LABEL: @sitofp_floor(
+; CHECK-NEXT:    [[CVT:%.*]] = sitofp i32 [[ARG:%.*]] to float
+; CHECK-NEXT:    ret float [[CVT]]
+;
+  %cvt = sitofp i32 %arg to float
+  %round = call float @llvm.floor.f32(float %cvt)
+  ret float %round
+}
+
+define float @uitofp_floor(i32 %arg) {
+; CHECK-LABEL: @uitofp_floor(
+; CHECK-NEXT:    [[CVT:%.*]] = uitofp i32 [[ARG:%.*]] to float
+; CHECK-NEXT:    [[ROUND:%.*]] = call float @llvm.floor.f32(float [[CVT]])
+; CHECK-NEXT:    ret float [[ROUND]]
+;
+  %cvt = uitofp i32 %arg to float
+  %round = call float @llvm.floor.f32(float %cvt)
+  ret float %round
+}
+
+define float @sitofp_trunc(i32 %arg) {
+; CHECK-LABEL: @sitofp_trunc(
+; CHECK-NEXT:    [[CVT:%.*]] = sitofp i32 [[ARG:%.*]] to float
+; CHECK-NEXT:    ret float [[CVT]]
+;
+  %cvt = sitofp i32 %arg to float
+  %round = call float @llvm.trunc.f32(float %cvt)
+  ret float %round
+}
+
+define float @uitofp_trunc(i32 %arg) {
+; CHECK-LABEL: @uitofp_trunc(
+; CHECK-NEXT:    [[CVT:%.*]] = uitofp i32 [[ARG:%.*]] to float
+; CHECK-NEXT:    [[ROUND:%.*]] = call float @llvm.trunc.f32(float [[CVT]])
+; CHECK-NEXT:    ret float [[ROUND]]
+;
+  %cvt = uitofp i32 %arg to float
+  %round = call float @llvm.trunc.f32(float %cvt)
+  ret float %round
+}
+
+define float @sitofp_round(i32 %arg) {
+; CHECK-LABEL: @sitofp_round(
+; CHECK-NEXT:    [[CVT:%.*]] = sitofp i32 [[ARG:%.*]] to float
+; CHECK-NEXT:    ret float [[CVT]]
+;
+  %cvt = sitofp i32 %arg to float
+  %round = call float @llvm.round.f32(float %cvt)
+  ret float %round
+}
+
+define float @uitofp_round(i32 %arg) {
+; CHECK-LABEL: @uitofp_round(
+; CHECK-NEXT:    [[CVT:%.*]] = uitofp i32 [[ARG:%.*]] to float
+; CHECK-NEXT:    [[ROUND:%.*]] = call float @llvm.round.f32(float [[CVT]])
+; CHECK-NEXT:    ret float [[ROUND]]
+;
+  %cvt = uitofp i32 %arg to float
+  %round = call float @llvm.round.f32(float %cvt)
+  ret float %round
+}
+
+define float @sitofp_nearbyint(i32 %arg) {
+; CHECK-LABEL: @sitofp_nearbyint(
+; CHECK-NEXT:    [[CVT:%.*]] = sitofp i32 [[ARG:%.*]] to float
+; CHECK-NEXT:    ret float [[CVT]]
+;
+  %cvt = sitofp i32 %arg to float
+  %nearbyint = call float @llvm.nearbyint.f32(float %cvt)
+  ret float %nearbyint
+}
+
+define float @uitofp_nearbyint(i32 %arg) {
+; CHECK-LABEL: @uitofp_nearbyint(
+; CHECK-NEXT:    [[CVT:%.*]] = uitofp i32 [[ARG:%.*]] to float
+; CHECK-NEXT:    [[NEARBYINT:%.*]] = call float @llvm.nearbyint.f32(float [[CVT]])
+; CHECK-NEXT:    ret float [[NEARBYINT]]
+;
+  %cvt = uitofp i32 %arg to float
+  %nearbyint = call float @llvm.nearbyint.f32(float %cvt)
+  ret float %nearbyint
+}
+
+define float @sitofp_rint(i32 %arg) {
+; CHECK-LABEL: @sitofp_rint(
+; CHECK-NEXT:    [[CVT:%.*]] = sitofp i32 [[ARG:%.*]] to float
+; CHECK-NEXT:    ret float [[CVT]]
+;
+  %cvt = sitofp i32 %arg to float
+  %rint = call float @llvm.rint.f32(float %cvt)
+  ret float %rint
+}
+
+define float @uitofp_rint(i32 %arg) {
+; CHECK-LABEL: @uitofp_rint(
+; CHECK-NEXT:    [[CVT:%.*]] = uitofp i32 [[ARG:%.*]] to float
+; CHECK-NEXT:    [[RINT:%.*]] = call float @llvm.rint.f32(float [[CVT]])
+; CHECK-NEXT:    ret float [[RINT]]
+;
+  %cvt = uitofp i32 %arg to float
+  %rint = call float @llvm.rint.f32(float %cvt)
+  ret float %rint
+}
+
+declare float @llvm.floor.f32(float) #0
+declare float @llvm.trunc.f32(float) #0
+declare float @llvm.round.f32(float) #0
+declare float @llvm.nearbyint.f32(float) #0
+declare float @llvm.rint.f32(float) #0
+
+attributes #0 = { nounwind readnone speculatable }