Index: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -830,11 +830,30 @@
   return nullptr;
 }
 
+/// \returns true if the test performed by llvm.is.fpclass(x, \p Mask) is
+/// equivalent to fcmp oeq x, 0.0 with the floating-point environment assumed
+/// for \p F for type \p Ty
+static bool fpclassTestIsFCmp0(FPClassTest Mask, const Function &F, Type *Ty) {
+  if (Mask == fcZero)
+    return F.getDenormalMode(Ty->getScalarType()->getFltSemantics()).Input ==
+           DenormalMode::IEEE;
+
+  if (Mask == (fcZero | fcSubnormal)) {
+    DenormalMode::DenormalModeKind InputMode =
+        F.getDenormalMode(Ty->getScalarType()->getFltSemantics()).Input;
+    return InputMode == DenormalMode::PreserveSign ||
+           InputMode == DenormalMode::PositiveZero;
+  }
+
+  return false;
+}
+
 Instruction *InstCombinerImpl::foldIntrinsicIsFPClass(IntrinsicInst &II) {
   Value *Src0 = II.getArgOperand(0);
   Value *Src1 = II.getArgOperand(1);
   const ConstantInt *CMask = cast<ConstantInt>(Src1);
   uint32_t Mask = CMask->getZExtValue();
+  uint32_t InvertedMask = ~CMask->getZExtValue() & fcAllFlags;
   const bool IsStrict = II.isStrictFP();
 
   Value *FNegSrc;
@@ -895,6 +914,28 @@
     return replaceInstUsesWith(II, FCmp);
   }
 
+  if (!IsStrict &&
+      fpclassTestIsFCmp0(static_cast<FPClassTest>(Mask),
+                         *II.getParent()->getParent(), Src0->getType())) {
+    // Equivalent of == 0.
+    Value *FCmp =
+        Builder.CreateFCmpOEQ(Src0, ConstantFP::get(Src0->getType(), 0.0));
+
+    FCmp->takeName(&II);
+    return replaceInstUsesWith(II, FCmp);
+  }
+
+  if (!IsStrict &&
+      fpclassTestIsFCmp0(static_cast<FPClassTest>(InvertedMask),
+                         *II.getParent()->getParent(), Src0->getType())) {
+    // Equivalent of !(x == 0).
+    Value *FCmp =
+        Builder.CreateFCmpUNE(Src0, ConstantFP::get(Src0->getType(), 0.0));
+
+    FCmp->takeName(&II);
+    return replaceInstUsesWith(II, FCmp);
+  }
+
   // fp_class (nnan x), qnan|snan|other -> fp_class (nnan x), other
   if ((Mask & fcNan) && isKnownNeverNaN(Src0, &getTargetLibraryInfo())) {
     II.setArgOperand(1, ConstantInt::get(Src1->getType(), Mask & ~fcNan));
Index: llvm/test/Transforms/InstCombine/is_fpclass.ll
===================================================================
--- llvm/test/Transforms/InstCombine/is_fpclass.ll
+++ llvm/test/Transforms/InstCombine/is_fpclass.ll
@@ -116,7 +116,7 @@
 
 define i1 @test_class_is_p0_n0_f32(float %x) {
 ; CHECK-LABEL: @test_class_is_p0_n0_f32(
-; CHECK-NEXT:    [[VAL:%.*]] = call i1 @llvm.is.fpclass.f32(float [[X:%.*]], i32 96)
+; CHECK-NEXT:    [[VAL:%.*]] = fcmp oeq float [[X:%.*]], 0.000000e+00
 ; CHECK-NEXT:    ret i1 [[VAL]]
 ;
   %val = call i1 @llvm.is.fpclass.f32(float %x, i32 96) ; fcZero
@@ -125,7 +125,7 @@
 
 define <2 x i1> @test_class_is_p0_n0_v2f32(<2 x float> %x) {
 ; CHECK-LABEL: @test_class_is_p0_n0_v2f32(
-; CHECK-NEXT:    [[VAL:%.*]] = call <2 x i1> @llvm.is.fpclass.v2f32(<2 x float> [[X:%.*]], i32 96)
+; CHECK-NEXT:    [[VAL:%.*]] = fcmp oeq <2 x float> [[X:%.*]], zeroinitializer
 ; CHECK-NEXT:    ret <2 x i1> [[VAL]]
 ;
   %val = call <2 x i1> @llvm.is.fpclass.v2f32(<2 x float> %x, i32 96) ; fcZero
@@ -170,7 +170,7 @@
 
 define i1 @test_class_is_not_p0_n0_f32(float %x) {
 ; CHECK-LABEL: @test_class_is_not_p0_n0_f32(
-; CHECK-NEXT:    [[VAL:%.*]] = call i1 @llvm.is.fpclass.f32(float [[X:%.*]], i32 927)
+; CHECK-NEXT:    [[VAL:%.*]] = fcmp une float [[X:%.*]], 0.000000e+00
 ; CHECK-NEXT:    ret i1 [[VAL]]
 ;
   %val = call i1 @llvm.is.fpclass.f32(float %x, i32 927) ; ~fcZero & fcAllFlags
@@ -179,7 +179,7 @@
 
 define <2 x i1> @test_class_is_not_p0_n0_v2f32(<2 x float> %x) {
 ; CHECK-LABEL: @test_class_is_not_p0_n0_v2f32(
-; CHECK-NEXT:    [[VAL:%.*]] = call <2 x i1> @llvm.is.fpclass.v2f32(<2 x float> [[X:%.*]], i32 927)
+; CHECK-NEXT:    [[VAL:%.*]] = fcmp une <2 x float> [[X:%.*]], zeroinitializer
 ; CHECK-NEXT:    ret <2 x i1> [[VAL]]
 ;
   %val = call <2 x i1> @llvm.is.fpclass.v2f32(<2 x float> %x, i32 927) ; ~fcZero & fcAllFlags
@@ -215,7 +215,7 @@
 
 define i1 @test_class_is_not_p0_n0_psub_nsub_f32_daz(float %x) "denormal-fp-math"="ieee,preserve-sign" {
 ; CHECK-LABEL: @test_class_is_not_p0_n0_psub_nsub_f32_daz(
-; CHECK-NEXT:    [[VAL:%.*]] = call i1 @llvm.is.fpclass.f32(float [[X:%.*]], i32 783)
+; CHECK-NEXT:    [[VAL:%.*]] = fcmp une float [[X:%.*]], 0.000000e+00
 ; CHECK-NEXT:    ret i1 [[VAL]]
 ;
   %val = call i1 @llvm.is.fpclass.f32(float %x, i32 783) ; ~(fcZero|fcSubnormal) & fcAllFlags
@@ -224,7 +224,7 @@
 
 define i1 @test_class_is_not_p0_n0_psub_nsub_f32_dapz(float %x) "denormal-fp-math"="ieee,positive-zero" {
 ; CHECK-LABEL: @test_class_is_not_p0_n0_psub_nsub_f32_dapz(
-; CHECK-NEXT:    [[VAL:%.*]] = call i1 @llvm.is.fpclass.f32(float [[X:%.*]], i32 783)
+; CHECK-NEXT:    [[VAL:%.*]] = fcmp une float [[X:%.*]], 0.000000e+00
 ; CHECK-NEXT:    ret i1 [[VAL]]
 ;
   %val = call i1 @llvm.is.fpclass.f32(float %x, i32 783) ; ~(fcZero|fcSubnormal) & fcAllFlags
@@ -278,7 +278,7 @@
 
 define i1 @test_class_is_p0_n0_psub_nsub_f32_daz(float %x) "denormal-fp-math"="ieee,preserve-sign" {
 ; CHECK-LABEL: @test_class_is_p0_n0_psub_nsub_f32_daz(
-; CHECK-NEXT:    [[VAL:%.*]] = call i1 @llvm.is.fpclass.f32(float [[X:%.*]], i32 240)
+; CHECK-NEXT:    [[VAL:%.*]] = fcmp oeq float [[X:%.*]], 0.000000e+00
 ; CHECK-NEXT:    ret i1 [[VAL]]
 ;
   %val = call i1 @llvm.is.fpclass.f32(float %x, i32 240) ; fcZero | fcSubnormal
@@ -287,7 +287,7 @@
 
 define i1 @test_class_is_p0_n0_psub_nsub_f32_dapz(float %x) "denormal-fp-math"="ieee,positive-zero" {
 ; CHECK-LABEL: @test_class_is_p0_n0_psub_nsub_f32_dapz(
-; CHECK-NEXT:    [[VAL:%.*]] = call i1 @llvm.is.fpclass.f32(float [[X:%.*]], i32 240)
+; CHECK-NEXT:    [[VAL:%.*]] = fcmp oeq float [[X:%.*]], 0.000000e+00
 ; CHECK-NEXT:    ret i1 [[VAL]]
 ;
   %val = call i1 @llvm.is.fpclass.f32(float %x, i32 240) ; fcZero | fcSubnormal
@@ -314,7 +314,7 @@
 
 define <2 x i1> @test_class_is_p0_n0_psub_nsub_v2f32_daz(<2 x float> %x) "denormal-fp-math"="ieee,preserve-sign" {
 ; CHECK-LABEL: @test_class_is_p0_n0_psub_nsub_v2f32_daz(
-; CHECK-NEXT:    [[VAL:%.*]] = call <2 x i1> @llvm.is.fpclass.v2f32(<2 x float> [[X:%.*]], i32 240)
+; CHECK-NEXT:    [[VAL:%.*]] = fcmp oeq <2 x float> [[X:%.*]], zeroinitializer
 ; CHECK-NEXT:    ret <2 x i1> [[VAL]]
 ;
   %val = call <2 x i1> @llvm.is.fpclass.v2f32(<2 x float> %x, i32 240) ; fcZero | fcSubnormal
@@ -323,7 +323,7 @@
 
 define <2 x i1> @test_class_is_p0_n0_psub_nsub_v2f32_dapz(<2 x float> %x) "denormal-fp-math"="ieee,positive-zero" {
 ; CHECK-LABEL: @test_class_is_p0_n0_psub_nsub_v2f32_dapz(
-; CHECK-NEXT:    [[VAL:%.*]] = call <2 x i1> @llvm.is.fpclass.v2f32(<2 x float> [[X:%.*]], i32 240)
+; CHECK-NEXT:    [[VAL:%.*]] = fcmp oeq <2 x float> [[X:%.*]], zeroinitializer
 ; CHECK-NEXT:    ret <2 x i1> [[VAL]]
 ;
   %val = call <2 x i1> @llvm.is.fpclass.v2f32(<2 x float> %x, i32 240) ; fcZero | fcSubnormal
@@ -1460,7 +1460,7 @@
 define i1 @test_class_fneg_zero(float %arg) {
 ;
 ; CHECK-LABEL: @test_class_fneg_zero(
-; CHECK-NEXT:    [[CLASS:%.*]] = call i1 @llvm.is.fpclass.f32(float [[ARG:%.*]], i32 96)
+; CHECK-NEXT:    [[CLASS:%.*]] = fcmp oeq float [[ARG:%.*]], 0.000000e+00
 ; CHECK-NEXT:    ret i1 [[CLASS]]
 ;
   %fneg = fneg float %arg
@@ -1715,7 +1715,7 @@
 ; -> poszero
 define i1 @test_class_fabs_poszero(float %arg) {
 ; CHECK-LABEL: @test_class_fabs_poszero(
-; CHECK-NEXT:    [[CLASS:%.*]] = call i1 @llvm.is.fpclass.f32(float [[ARG:%.*]], i32 96)
+; CHECK-NEXT:    [[CLASS:%.*]] = fcmp oeq float [[ARG:%.*]], 0.000000e+00
 ; CHECK-NEXT:    ret i1 [[CLASS]]
 ;
   %fabs = call float @llvm.fabs.f32(float %arg)
@@ -1792,7 +1792,7 @@
 ; -> poszero
 define i1 @test_class_fabs_zero(float %arg) {
 ; CHECK-LABEL: @test_class_fabs_zero(
-; CHECK-NEXT:    [[CLASS:%.*]] = call i1 @llvm.is.fpclass.f32(float [[ARG:%.*]], i32 96)
+; CHECK-NEXT:    [[CLASS:%.*]] = fcmp oeq float [[ARG:%.*]], 0.000000e+00
 ; CHECK-NEXT:    ret i1 [[CLASS]]
 ;
   %fabs = call float @llvm.fabs.f32(float %arg)
@@ -2038,7 +2038,7 @@
 
 define i1 @test_class_fneg_fabs_negzero(float %arg) {
 ; CHECK-LABEL: @test_class_fneg_fabs_negzero(
-; CHECK-NEXT:    [[CLASS:%.*]] = call i1 @llvm.is.fpclass.f32(float [[ARG:%.*]], i32 96)
+; CHECK-NEXT:    [[CLASS:%.*]] = fcmp oeq float [[ARG:%.*]], 0.000000e+00
 ; CHECK-NEXT:    ret i1 [[CLASS]]
 ;
   %fabs = call float @llvm.fabs.f32(float %arg)
@@ -2122,7 +2122,7 @@
 
 define i1 @test_class_fneg_fabs_zero(float %arg) {
 ; CHECK-LABEL: @test_class_fneg_fabs_zero(
-; CHECK-NEXT:    [[CLASS:%.*]] = call i1 @llvm.is.fpclass.f32(float [[ARG:%.*]], i32 96)
+; CHECK-NEXT:    [[CLASS:%.*]] = fcmp oeq float [[ARG:%.*]], 0.000000e+00
 ; CHECK-NEXT:    ret i1 [[CLASS]]
 ;
   %fabs = call float @llvm.fabs.f32(float %arg)