Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -4583,6 +4583,8 @@
 def m80387 : Flag<["-"], "m80387">, Alias<mx87>;
 def mno_80387 : Flag<["-"], "mno-80387">, Alias<mno_x87>;
 def mno_fp_ret_in_387 : Flag<["-"], "mno-fp-ret-in-387">, Alias<mno_x87>;
+def mpc80 : Flag<["-"], "mpc80">, Group<m_x86_Features_Group>;
+def mno_pc80 : Flag<["-"], "mno-pc80">, Group<m_x86_Features_Group>;
 def mmmx : Flag<["-"], "mmmx">, Group<m_x86_Features_Group>;
 def mno_mmx : Flag<["-"], "mno-mmx">, Group<m_x86_Features_Group>;
 def m3dnow : Flag<["-"], "m3dnow">, Group<m_x86_Features_Group>;
Index: clang/lib/Basic/Targets/X86.h
===================================================================
--- clang/lib/Basic/Targets/X86.h
+++ clang/lib/Basic/Targets/X86.h
@@ -155,6 +155,7 @@
   bool HasUINTR = false;
   bool HasCRC32 = false;
   bool HasX87 = false;
+  bool HasPC80 = false;
 
 protected:
   llvm::X86::CPUKind CPU = llvm::X86::CK_None;
Index: clang/lib/Basic/Targets/X86.cpp
===================================================================
--- clang/lib/Basic/Targets/X86.cpp
+++ clang/lib/Basic/Targets/X86.cpp
@@ -356,6 +356,8 @@
       HasCRC32 = true;
     } else if (Feature == "+x87") {
       HasX87 = true;
+    } else if (Feature == "+pc80") {
+      HasPC80 = true;
     }
 
     X86SSEEnum Level = llvm::StringSwitch<X86SSEEnum>(Feature)
@@ -1070,6 +1072,7 @@
       .Case("movdiri", HasMOVDIRI)
       .Case("movdir64b", HasMOVDIR64B)
       .Case("mwaitx", HasMWAITX)
+      .Case("pc80", HasPC80)
       .Case("pclmul", HasPCLMUL)
       .Case("pconfig", HasPCONFIG)
       .Case("pku", HasPKU)
Index: llvm/include/llvm/TargetParser/X86TargetParser.def
===================================================================
--- llvm/include/llvm/TargetParser/X86TargetParser.def
+++ llvm/include/llvm/TargetParser/X86TargetParser.def
@@ -189,6 +189,7 @@
 X86_FEATURE       (MOVDIR64B,       "movdir64b")
 X86_FEATURE       (MOVDIRI,         "movdiri")
 X86_FEATURE       (MWAITX,          "mwaitx")
+X86_FEATURE       (PC80,            "pc80")
 X86_FEATURE       (PCONFIG,         "pconfig")
 X86_FEATURE       (PKU,             "pku")
 X86_FEATURE       (PREFETCHI,       "prefetchi")
Index: llvm/lib/Target/X86/X86.td
===================================================================
--- llvm/lib/Target/X86/X86.td
+++ llvm/lib/Target/X86/X86.td
@@ -33,6 +33,10 @@
 def FeatureX87     : SubtargetFeature<"x87","HasX87", "true",
                                       "Enable X87 float instructions">;
 
+def FeaturePC80    : SubtargetFeature<"pc80", "HasPC80", "true",
+                                      "Enable X87 float instructions with 80-bit FP",
+                                      [FeatureX87]>;
+
 def FeatureNOPL    : SubtargetFeature<"nopl", "HasNOPL", "true",
                                       "Enable NOPL instruction (generally pentium pro+)">;
 
Index: llvm/lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- llvm/lib/Target/X86/X86ISelLowering.cpp
+++ llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -21368,6 +21368,10 @@
   if (VT == MVT::f128 || !Subtarget.hasX87())
     return SDValue();
 
+  if (SrcVT == MVT::i64 && UseSSEReg && Subtarget.isOSWindows() &&
+      !Subtarget.hasPC80())
+    return SDValue();
+
   SDValue ValueToStore = Src;
   if (SrcVT == MVT::i64 && Subtarget.hasSSE2() && !Subtarget.is64Bit())
     // Bitcasting to f64 here allows us to do a single 64-bit store from
@@ -21824,7 +21828,9 @@
   if (SDValue Extract = vectorizeExtractedCast(Op, DAG, Subtarget))
     return Extract;
 
-  if (Subtarget.hasAVX512() && isScalarFPTypeInSSEReg(DstVT) &&
+  bool UseSSEReg = isScalarFPTypeInSSEReg(DstVT);
+
+  if (Subtarget.hasAVX512() && UseSSEReg &&
       (SrcVT == MVT::i32 || (SrcVT == MVT::i64 && Subtarget.is64Bit()))) {
     // Conversions from unsigned i32 to f32/f64 are legal,
     // using VCVTUSI2SS/SD.  Same for i64 in 64-bit mode.
@@ -21859,6 +21865,9 @@
       (DstVT == MVT::f32 || DstVT == MVT::f64))
     return SDValue();
 
+  if (!Subtarget.hasX87())
+    return SDValue();
+
   // Make a 64-bit buffer, and use it to build an FILD.
   SDValue StackSlot = DAG.CreateStackTemporary(MVT::i64, 8);
   int SSFI = cast<FrameIndexSDNode>(StackSlot)->getIndex();
@@ -21880,6 +21889,10 @@
   }
 
   assert(SrcVT == MVT::i64 && "Unexpected type in UINT_TO_FP");
+
+  if (UseSSEReg && Subtarget.isOSWindows() && !Subtarget.hasPC80())
+    return SDValue();
+
   SDValue ValueToStore = Src;
   if (isScalarFPTypeInSSEReg(Op.getValueType()) && !Subtarget.is64Bit()) {
     // Bitcasting to f64 here allows us to do a single 64-bit store from
Index: llvm/lib/TargetParser/X86TargetParser.cpp
===================================================================
--- llvm/lib/TargetParser/X86TargetParser.cpp
+++ llvm/lib/TargetParser/X86TargetParser.cpp
@@ -510,6 +510,7 @@
 constexpr FeatureBitset ImpliedFeaturesMOVBE = {};
 constexpr FeatureBitset ImpliedFeaturesMOVDIR64B = {};
 constexpr FeatureBitset ImpliedFeaturesMOVDIRI = {};
+constexpr FeatureBitset ImpliedFeaturesPC80 = {};
 constexpr FeatureBitset ImpliedFeaturesPCONFIG = {};
 constexpr FeatureBitset ImpliedFeaturesPOPCNT = {};
 constexpr FeatureBitset ImpliedFeaturesPKU = {};