[AVX-512] Add support for lowering fp_to_f16 and f16_to_fp when VLX is supported regardless of whether F16C is also supported.

Still need to add support for lowering using AVX512F when neither VLX or F16C is supported.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@281884 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/X86/X86ISelLowering.cpp

@@ -349,7 +349,8 @@ X86TargetLowering::X86TargetLowering(const X86TargetMachine &TM,
   // Special handling for half-precision floating point conversions.
   // If we don't have F16C support, then lower half float conversions
   // into library calls.
-  if (Subtarget.useSoftFloat() || !Subtarget.hasF16C()) {
+  if (Subtarget.useSoftFloat() ||
+      (!Subtarget.hasF16C() && !Subtarget.hasVLX())) {
     setOperationAction(ISD::FP16_TO_FP, MVT::f32, Expand);
     setOperationAction(ISD::FP_TO_FP16, MVT::f32, Expand);
   }

lib/Target/X86/X86InstrAVX512.td

@@ -6295,6 +6295,26 @@ let Predicates = [HasAVX512] in {
   }
 }
 
+// Patterns for  matching conversions from float to half-float and vice versa.
+let Predicates = [HasVLX] in {
+  // Use MXCSR.RC for rounding instead of explicitly specifying the default
+  // rounding mode (Nearest-Even, encoded as 0). Both are equivalent in the
+  // configurations we support (the default). However, falling back to MXCSR is
+  // more consistent with other instructions, which are always controlled by it.
+  // It's encoded as 0b100.
+  def : Pat<(fp_to_f16 FR32X:$src),
+            (i16 (EXTRACT_SUBREG (VMOVPDI2DIZrr (VCVTPS2PHZ128rr
+              (COPY_TO_REGCLASS FR32X:$src, VR128X), 4)), sub_16bit))>;
+
+  def : Pat<(f16_to_fp GR16:$src),
+            (f32 (COPY_TO_REGCLASS (VCVTPH2PSZ128rr
+              (COPY_TO_REGCLASS (MOVSX32rr16 GR16:$src), VR128X)), FR32X)) >;
+
+  def : Pat<(f16_to_fp (i16 (fp_to_f16 FR32X:$src))),
+            (f32 (COPY_TO_REGCLASS (VCVTPH2PSZ128rr
+              (VCVTPS2PHZ128rr (COPY_TO_REGCLASS FR32X:$src, VR128X), 4)), FR32X)) >;
+}
+
 //  Unordered/Ordered scalar fp compare with Sea and set EFLAGS
 multiclass avx512_ord_cmp_sae<bits<8> opc, X86VectorVTInfo _, SDNode OpNode,
                             string OpcodeStr> {

lib/Target/X86/X86InstrSSE.td

@@ -8227,7 +8227,7 @@ let Predicates = [HasF16C] in {
 }
 
 // Patterns for  matching conversions from float to half-float and vice versa.
-let Predicates = [HasF16C] in {
+let Predicates = [HasF16C, NoVLX] in {
   // Use MXCSR.RC for rounding instead of explicitly specifying the default
   // rounding mode (Nearest-Even, encoded as 0). Both are equivalent in the
   // configurations we support (the default). However, falling back to MXCSR is