[SelectionDAG][X86] Support f16 in getReciprocalOpName.

[craig.topper]

Summary

If the "reciprocal-estimates" attribute is present and it doesn't
contain "all", "none", or "default", we previously crashed on f16
operations.

This patch addes an 'h' suffix' to prevent the crash.

I've added simple tests that just enable the estimate for all
vec-sqrt and one test case that explicitly tests the new 'h' suffix
to override the default steps.

There may be some frontend change needed to, but I haven't checked
that yet.

[craig.topper]

Committed by accident

[pengfei]

Yeah, at least driver parsing. We can do it as follow up. LGTM.

llvm/lib/CodeGen/TargetLoweringBase.cpp

 /// This string should match the corresponding option to the front-end's
 /// "-mrecip" flag assuming those strings have been passed through in an
 /// attribute string. For example, "vec-divf" for a division of a vXf32.
 static std::string getReciprocalOpName(bool IsSqrt, EVT VT) {
   std::string Name = VT.isVector() ? "vec-" : "";
 
   Name += IsSqrt ? "sqrt" : "div";
 
-  // TODO: Handle "half" or other float types?
+  // TODO: Handle other float types?
   if (VT.getScalarType() == MVT::f64) {
     Name += "d";
+  } else if (VT.getScalarType() == MVT::f16) {
+    Name += "h";
   } else {
     assert(VT.getScalarType() == MVT::f32 &&
            "Unexpected FP type for reciprocal estimate");
     Name += "f";
   }
 
   return Name;
 }

llvm/test/CodeGen/X86/avx512fp16-intrinsics.ll

 ; CHECK-NEXT:    vrsqrtph %zmm0, %zmm0
 ; CHECK-NEXT:    vmulph %zmm0, %zmm1, %zmm0
 ; CHECK-NEXT:    retq
   %1 = call fast <32 x half> @llvm.sqrt.v32f16(<32 x half> %a0)
   %2 = fdiv fast <32 x half> %a1, %1
   ret <32 x half> %2
 }
 
+define <32 x half> @test_sqrt_ph_512_fast_estimate_attribute(<32 x half> %a0, <32 x half> %a1) "reciprocal-estimates"="vec-sqrt" {
+; CHECK-LABEL: test_sqrt_ph_512_fast_estimate_attribute:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vrsqrtph %zmm0, %zmm0
+; CHECK-NEXT:    vmulph %zmm0, %zmm1, %zmm0
+; CHECK-NEXT:    retq
+  %1 = call fast <32 x half> @llvm.sqrt.v32f16(<32 x half> %a0)
+  %2 = fdiv fast <32 x half> %a1, %1
+  ret <32 x half> %2
+}
+
+define <32 x half> @test_sqrt_ph_512_fast_estimate_attribute_2(<32 x half> %a0, <32 x half> %a1) "reciprocal-estimates"="vec-sqrth:1" {
+; CHECK-LABEL: test_sqrt_ph_512_fast_estimate_attribute_2:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vrsqrtph %zmm0, %zmm2
+; CHECK-NEXT:    vmulph %zmm2, %zmm0, %zmm0
+; CHECK-NEXT:    vfmadd213ph {{\.?LCPI[0-9]+_[0-9]+}}(%rip){1to32}, %zmm2, %zmm0
+; CHECK-NEXT:    vmulph {{\.?LCPI[0-9]+_[0-9]+}}(%rip){1to32}, %zmm2, %zmm2
+; CHECK-NEXT:    vmulph %zmm1, %zmm0, %zmm0
+; CHECK-NEXT:    vmulph %zmm0, %zmm2, %zmm0
+; CHECK-NEXT:    retq
+  %1 = call fast <32 x half> @llvm.sqrt.v32f16(<32 x half> %a0)
+  %2 = fdiv fast <32 x half> %a1, %1
+  ret <32 x half> %2
+}
+
 define <32 x half> @test_mask_sqrt_ph_512(<32 x half> %a0, <32 x half> %passthru, i32 %mask) {
 ; CHECK-LABEL: test_mask_sqrt_ph_512:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    kmovd %edi, %k1
 ; CHECK-NEXT:    vsqrtph %zmm0, %zmm1 {%k1}
 ; CHECK-NEXT:    vmovaps %zmm1, %zmm0
 ; CHECK-NEXT:    retq
   %1 = call <32 x half> @llvm.sqrt.v32f16(<32 x half> %a0)