Index: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -8101,9 +8101,14 @@
   // Some checks can be implemented using float comparisons, if floating point
   // exceptions are ignored.
   if (Flags.hasNoFPExcept() &&
-      // TODO: Should check isCondCodeLegal
       isOperationLegalOrCustom(ISD::SETCC, OperandVT.getScalarType())) {
-    if (isFCmpEqualZero(Test, Semantics, DAG.getMachineFunction())) {
+    // Even if the condition isn't legal, we're probably better off expanding it
+    // if it's the combined 0 || denormal compare.
+
+    if (isFCmpEqualZero(Test, Semantics, DAG.getMachineFunction()) &&
+        (Test != fcZero ||
+         isCondCodeLegalOrCustom(IsInverted ? ISD::SETUNE : ISD::SETOEQ,
+                                 OperandVT.getScalarType().getSimpleVT()))) {
       // If denormals could be implicitly treated as 0, this is not equivalent
       // to a compare with 0 since it will also be true for denormals.
       return DAG.getSetCC(DL, ResultVT, Op,
@@ -8111,9 +8116,12 @@
                           IsInverted ? ISD::SETUNE : ISD::SETOEQ);
     }
 
-    if (Test == fcNan)
+    if (Test == fcNan &&
+        isCondCodeLegalOrCustom(IsInverted ? ISD::SETO : ISD::SETUO,
+                                OperandVT.getScalarType().getSimpleVT())) {
       return DAG.getSetCC(DL, ResultVT, Op, Op,
                           IsInverted ? ISD::SETO : ISD::SETUO);
+    }
   }
 
   // In the general case use integer operations.
Index: llvm/test/CodeGen/X86/is_fpclass-fp80.ll
===================================================================
--- llvm/test/CodeGen/X86/is_fpclass-fp80.ll
+++ llvm/test/CodeGen/X86/is_fpclass-fp80.ll
@@ -160,26 +160,19 @@
 define i1 @is_zero_f80(x86_fp80 %x) {
 ; CHECK-32-LABEL: is_zero_f80:
 ; CHECK-32:       # %bb.0: # %entry
-; CHECK-32-NEXT:    fldt {{[0-9]+}}(%esp)
-; CHECK-32-NEXT:    fldz
-; CHECK-32-NEXT:    fucompp
-; CHECK-32-NEXT:    fnstsw %ax
-; CHECK-32-NEXT:    # kill: def $ah killed $ah killed $ax
-; CHECK-32-NEXT:    sahf
-; CHECK-32-NEXT:    setnp %cl
+; CHECK-32-NEXT:    movzwl {{[0-9]+}}(%esp), %eax
+; CHECK-32-NEXT:    andl $32767, %eax # imm = 0x7FFF
+; CHECK-32-NEXT:    orl {{[0-9]+}}(%esp), %eax
+; CHECK-32-NEXT:    orl {{[0-9]+}}(%esp), %eax
 ; CHECK-32-NEXT:    sete %al
-; CHECK-32-NEXT:    andb %cl, %al
 ; CHECK-32-NEXT:    retl
 ;
 ; CHECK-64-LABEL: is_zero_f80:
 ; CHECK-64:       # %bb.0: # %entry
-; CHECK-64-NEXT:    fldt {{[0-9]+}}(%rsp)
-; CHECK-64-NEXT:    fldz
-; CHECK-64-NEXT:    fucompi %st(1), %st
-; CHECK-64-NEXT:    fstp %st(0)
-; CHECK-64-NEXT:    setnp %cl
+; CHECK-64-NEXT:    movzwl {{[0-9]+}}(%rsp), %eax
+; CHECK-64-NEXT:    andl $32767, %eax # imm = 0x7FFF
+; CHECK-64-NEXT:    orq {{[0-9]+}}(%rsp), %rax
 ; CHECK-64-NEXT:    sete %al
-; CHECK-64-NEXT:    andb %cl, %al
 ; CHECK-64-NEXT:    retq
 entry:
   %0 = tail call i1 @llvm.is.fpclass.f80(x86_fp80 %x, i32 96)  ; 0x60 = "zero"
Index: llvm/test/CodeGen/X86/is_fpclass.ll
===================================================================
--- llvm/test/CodeGen/X86/is_fpclass.ll
+++ llvm/test/CodeGen/X86/is_fpclass.ll
@@ -684,24 +684,15 @@
 define i1 @iszero_f(float %x) {
 ; CHECK-32-LABEL: iszero_f:
 ; CHECK-32:       # %bb.0: # %entry
-; CHECK-32-NEXT:    flds {{[0-9]+}}(%esp)
-; CHECK-32-NEXT:    fldz
-; CHECK-32-NEXT:    fucompp
-; CHECK-32-NEXT:    fnstsw %ax
-; CHECK-32-NEXT:    # kill: def $ah killed $ah killed $ax
-; CHECK-32-NEXT:    sahf
-; CHECK-32-NEXT:    setnp %cl
+; CHECK-32-NEXT:    testl $2147483647, {{[0-9]+}}(%esp) # imm = 0x7FFFFFFF
 ; CHECK-32-NEXT:    sete %al
-; CHECK-32-NEXT:    andb %cl, %al
 ; CHECK-32-NEXT:    retl
 ;
 ; CHECK-64-LABEL: iszero_f:
 ; CHECK-64:       # %bb.0: # %entry
-; CHECK-64-NEXT:    xorps %xmm1, %xmm1
-; CHECK-64-NEXT:    cmpeqss %xmm0, %xmm1
-; CHECK-64-NEXT:    movd %xmm1, %eax
-; CHECK-64-NEXT:    andl $1, %eax
-; CHECK-64-NEXT:    # kill: def $al killed $al killed $eax
+; CHECK-64-NEXT:    movd %xmm0, %eax
+; CHECK-64-NEXT:    testl $2147483647, %eax # imm = 0x7FFFFFFF
+; CHECK-64-NEXT:    sete %al
 ; CHECK-64-NEXT:    retq
 entry:
   %0 = tail call i1 @llvm.is.fpclass.f32(float %x, i32 96)  ; 0x60 = "zero"
@@ -747,24 +738,15 @@
 define i1 @not_iszero_f(float %x) {
 ; CHECK-32-LABEL: not_iszero_f:
 ; CHECK-32:       # %bb.0: # %entry
-; CHECK-32-NEXT:    flds {{[0-9]+}}(%esp)
-; CHECK-32-NEXT:    fldz
-; CHECK-32-NEXT:    fucompp
-; CHECK-32-NEXT:    fnstsw %ax
-; CHECK-32-NEXT:    # kill: def $ah killed $ah killed $ax
-; CHECK-32-NEXT:    sahf
-; CHECK-32-NEXT:    setp %cl
+; CHECK-32-NEXT:    testl $2147483647, {{[0-9]+}}(%esp) # imm = 0x7FFFFFFF
 ; CHECK-32-NEXT:    setne %al
-; CHECK-32-NEXT:    orb %cl, %al
 ; CHECK-32-NEXT:    retl
 ;
 ; CHECK-64-LABEL: not_iszero_f:
 ; CHECK-64:       # %bb.0: # %entry
-; CHECK-64-NEXT:    xorps %xmm1, %xmm1
-; CHECK-64-NEXT:    cmpneqss %xmm0, %xmm1
-; CHECK-64-NEXT:    movd %xmm1, %eax
-; CHECK-64-NEXT:    andl $1, %eax
-; CHECK-64-NEXT:    # kill: def $al killed $al killed $eax
+; CHECK-64-NEXT:    movd %xmm0, %eax
+; CHECK-64-NEXT:    testl $2147483647, %eax # imm = 0x7FFFFFFF
+; CHECK-64-NEXT:    setne %al
 ; CHECK-64-NEXT:    retq
 entry:
   %0 = tail call i1 @llvm.is.fpclass.f32(float %x, i32 927)  ; ~0x60 = "~zero"
@@ -1293,24 +1275,18 @@
 define i1 @iszero_d(double %x) {
 ; CHECK-32-LABEL: iszero_d:
 ; CHECK-32:       # %bb.0: # %entry
-; CHECK-32-NEXT:    fldl {{[0-9]+}}(%esp)
-; CHECK-32-NEXT:    fldz
-; CHECK-32-NEXT:    fucompp
-; CHECK-32-NEXT:    fnstsw %ax
-; CHECK-32-NEXT:    # kill: def $ah killed $ah killed $ax
-; CHECK-32-NEXT:    sahf
-; CHECK-32-NEXT:    setnp %cl
+; CHECK-32-NEXT:    movl $2147483647, %eax # imm = 0x7FFFFFFF
+; CHECK-32-NEXT:    andl {{[0-9]+}}(%esp), %eax
+; CHECK-32-NEXT:    orl {{[0-9]+}}(%esp), %eax
 ; CHECK-32-NEXT:    sete %al
-; CHECK-32-NEXT:    andb %cl, %al
 ; CHECK-32-NEXT:    retl
 ;
 ; CHECK-64-LABEL: iszero_d:
 ; CHECK-64:       # %bb.0: # %entry
-; CHECK-64-NEXT:    xorpd %xmm1, %xmm1
-; CHECK-64-NEXT:    cmpeqsd %xmm0, %xmm1
-; CHECK-64-NEXT:    movq %xmm1, %rax
-; CHECK-64-NEXT:    andl $1, %eax
-; CHECK-64-NEXT:    # kill: def $al killed $al killed $rax
+; CHECK-64-NEXT:    movq %xmm0, %rax
+; CHECK-64-NEXT:    shlq %rax
+; CHECK-64-NEXT:    testq %rax, %rax
+; CHECK-64-NEXT:    sete %al
 ; CHECK-64-NEXT:    retq
 entry:
   %0 = tail call i1 @llvm.is.fpclass.f64(double %x, i32 96)  ; 0x60 = "zero"