Reland "Reland "[X86][RFC] Enable _Float16 type support on X86 following the psABI""

Fixed the missing SQRT promotion. Adding several missing operations too.

Author: phoebewang

llvm/docs/ReleaseNotes.rst

@@ -138,7 +138,7 @@ Changes to the WebAssembly Backend
 Changes to the X86 Backend
 --------------------------
 
-* ...
+* Support ``half`` type on SSE2 and above targets.
 
 Changes to the OCaml bindings
 -----------------------------

llvm/lib/Target/X86/X86FastISel.cpp

@@ -148,8 +148,7 @@ class X86FastISel final : public FastISel {
   /// computed in an SSE register, not on the X87 floating point stack.
   bool isScalarFPTypeInSSEReg(EVT VT) const {
     return (VT == MVT::f64 && Subtarget->hasSSE2()) ||
-           (VT == MVT::f32 && Subtarget->hasSSE1()) ||
-           (VT == MVT::f16 && Subtarget->hasFP16());
+           (VT == MVT::f32 && Subtarget->hasSSE1()) || VT == MVT::f16;
   }
 
   bool isTypeLegal(Type *Ty, MVT &VT, bool AllowI1 = false);
@@ -2281,12 +2280,13 @@ bool X86FastISel::X86FastEmitPseudoSelect(MVT RetVT, const Instruction *I) {
   default: return false;
   case MVT::i8:  Opc = X86::CMOV_GR8;   break;
   case MVT::i16: Opc = X86::CMOV_GR16;  break;
-  case MVT::f16: Opc = X86::CMOV_FR16X; break;
   case MVT::i32: Opc = X86::CMOV_GR32;  break;
-  case MVT::f32: Opc = Subtarget->hasAVX512() ? X86::CMOV_FR32X
-                                              : X86::CMOV_FR32; break;
-  case MVT::f64: Opc = Subtarget->hasAVX512() ? X86::CMOV_FR64X
-                                              : X86::CMOV_FR64; break;
+  case MVT::f16:
+    Opc = Subtarget->hasAVX512() ? X86::CMOV_FR16X : X86::CMOV_FR16; break;
+  case MVT::f32:
+    Opc = Subtarget->hasAVX512() ? X86::CMOV_FR32X : X86::CMOV_FR32; break;
+  case MVT::f64:
+    Opc = Subtarget->hasAVX512() ? X86::CMOV_FR64X : X86::CMOV_FR64; break;
   }
 
   const Value *Cond = I->getOperand(0);
@@ -3903,6 +3903,9 @@ unsigned X86FastISel::fastMaterializeFloatZero(const ConstantFP *CF) {
   unsigned Opc = 0;
   switch (VT.SimpleTy) {
   default: return 0;
+  case MVT::f16:
+    Opc = HasAVX512 ? X86::AVX512_FsFLD0SH : X86::FsFLD0SH;
+    break;
   case MVT::f32:
     Opc = HasAVX512 ? X86::AVX512_FsFLD0SS
           : HasSSE1 ? X86::FsFLD0SS