[RISCV] Support F16 vectors with Zfhmin+Zvfh.

[craig.topper]

Summary

I've enabled Zfhmin on 2 basic tests to show this isn't
completely broken.

[monkchiang]

LGTM

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

bool RISCVTargetLowering::isVScaleKnownToBeAPowerOfTwo() const {
   assert(Subtarget.getRealMinVLen() >= 64 && "zve32* unsupported");
   static_assert(RISCV::RVVBitsPerBlock == 64,
                 "RVVBitsPerBlock changed, audit needed");
   return true;
 }
 
 bool RISCVTargetLowering::isFMAFasterThanFMulAndFAdd(const MachineFunction &MF,
                                                      EVT VT) const {
-  VT = VT.getScalarType();
+  EVT SVT = VT.getScalarType();
 
-  if (!VT.isSimple())
+  if (!SVT.isSimple())
     return false;
 
-  switch (VT.getSimpleVT().SimpleTy) {
+  switch (SVT.getSimpleVT().SimpleTy) {
   case MVT::f16:
-    return Subtarget.hasStdExtZfh();
+    return VT.isVector() ? Subtarget.hasVInstructionsF16()
+                         : Subtarget.hasStdExtZfh();
   case MVT::f32:
     return Subtarget.hasStdExtF();
   case MVT::f64:
     return Subtarget.hasStdExtD();
   default:
     break;
   }
 

llvm/lib/Target/RISCV/RISCVSubtarget.h

bool isRegisterReservedByUser(Register i) const {
     return UserReservedRegister[i];
   }
 
   bool hasMacroFusion() const { return hasLUIADDIFusion(); }
 
   // Vector codegen related methods.
   bool hasVInstructions() const { return HasStdExtZve32x; }
   bool hasVInstructionsI64() const { return HasStdExtZve64x; }
-  bool hasVInstructionsF16() const { return HasStdExtZvfh && HasStdExtZfh; }
+  bool hasVInstructionsF16() const {
+    return HasStdExtZvfh && hasStdExtZfhOrZfhmin();
+  }
   // FIXME: Consider Zfinx in the future
   bool hasVInstructionsF32() const { return HasStdExtZve32f && HasStdExtF; }
   // FIXME: Consider Zdinx in the future
   bool hasVInstructionsF64() const { return HasStdExtZve64d && HasStdExtD; }
   // F16 and F64 both require F32.
   bool hasVInstructionsAnyF() const { return hasVInstructionsF32(); }
   unsigned getMaxInterleaveFactor() const {
     return hasVInstructions() ? MaxInterleaveFactor : 1;

llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp.ll

 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
 ; RUN: llc -mtriple=riscv32 -target-abi=ilp32d -mattr=+v,+zfh,+experimental-zvfh,+f,+d -riscv-v-vector-bits-min=128 -riscv-v-fixed-length-vector-lmul-max=2 -verify-machineinstrs < %s | FileCheck %s --check-prefixes=CHECK,LMULMAX2
 ; RUN: llc -mtriple=riscv64 -target-abi=lp64d -mattr=+v,+zfh,+experimental-zvfh,+f,+d -riscv-v-vector-bits-min=128 -riscv-v-fixed-length-vector-lmul-max=2 -verify-machineinstrs < %s | FileCheck %s --check-prefixes=CHECK,LMULMAX2
 ; RUN: llc -mtriple=riscv32 -target-abi=ilp32d -mattr=+v,+zfh,+experimental-zvfh,+f,+d -riscv-v-vector-bits-min=128 -riscv-v-fixed-length-vector-lmul-max=1 -verify-machineinstrs < %s | FileCheck %s --check-prefixes=CHECK,LMULMAX1,LMULMAX1-RV32
 ; RUN: llc -mtriple=riscv64 -target-abi=lp64d -mattr=+v,+zfh,+experimental-zvfh,+f,+d -riscv-v-vector-bits-min=128 -riscv-v-fixed-length-vector-lmul-max=1 -verify-machineinstrs < %s | FileCheck %s --check-prefixes=CHECK,LMULMAX1,LMULMAX1-RV64
+; RUN: llc -mtriple=riscv32 -target-abi=ilp32d -mattr=+v,+zfhmin,+experimental-zvfh,+f,+d -riscv-v-vector-bits-min=128 -riscv-v-fixed-length-vector-lmul-max=2 -verify-machineinstrs < %s | FileCheck %s --check-prefixes=CHECK,LMULMAX2
+; RUN: llc -mtriple=riscv64 -target-abi=lp64d -mattr=+v,+zfhmin,+experimental-zvfh,+f,+d -riscv-v-vector-bits-min=128 -riscv-v-fixed-length-vector-lmul-max=2 -verify-machineinstrs < %s | FileCheck %s --check-prefixes=CHECK,LMULMAX2
+; RUN: llc -mtriple=riscv32 -target-abi=ilp32d -mattr=+v,+zfhmin,+experimental-zvfh,+f,+d -riscv-v-vector-bits-min=128 -riscv-v-fixed-length-vector-lmul-max=1 -verify-machineinstrs < %s | FileCheck %s --check-prefixes=CHECK,LMULMAX1,LMULMAX1-RV32
+; RUN: llc -mtriple=riscv64 -target-abi=lp64d -mattr=+v,+zfhmin,+experimental-zvfh,+f,+d -riscv-v-vector-bits-min=128 -riscv-v-fixed-length-vector-lmul-max=1 -verify-machineinstrs < %s | FileCheck %s --check-prefixes=CHECK,LMULMAX1,LMULMAX1-RV64
 
 define void @fadd_v8f16(<8 x half>* %x, <8 x half>* %y) {
 ; CHECK-LABEL: fadd_v8f16:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vsetivli zero, 8, e16, m1, ta, ma
 ; CHECK-NEXT:    vle16.v v8, (a0)
 ; CHECK-NEXT:    vle16.v v9, (a1)
 ; CHECK-NEXT:    vfadd.vv v8, v8, v9

llvm/test/CodeGen/RISCV/rvv/vfadd.ll

 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
 ; RUN: sed 's/iXLen/i32/g' %s | llc -mtriple=riscv32 -mattr=+v,+zfh,+experimental-zvfh \
 ; RUN:   -verify-machineinstrs -target-abi=ilp32d | FileCheck %s
 ; RUN: sed 's/iXLen/i64/g' %s | llc -mtriple=riscv64 -mattr=+v,+zfh,+experimental-zvfh \
 ; RUN:   -verify-machineinstrs -target-abi=lp64d | FileCheck %s
+; RUN: sed 's/iXLen/i32/g' %s | llc -mtriple=riscv32 -mattr=+v,+zfhmin,+experimental-zvfh \
+; RUN:   -verify-machineinstrs -target-abi=ilp32d | FileCheck %s
+; RUN: sed 's/iXLen/i64/g' %s | llc -mtriple=riscv64 -mattr=+v,+zfhmin,+experimental-zvfh \
+; RUN:   -verify-machineinstrs -target-abi=lp64d | FileCheck %s
 declare <vscale x 1 x half> @llvm.riscv.vfadd.nxv1f16.nxv1f16(
   <vscale x 1 x half>,
   <vscale x 1 x half>,
   <vscale x 1 x half>,
   iXLen);
 
 define <vscale x 1 x half> @intrinsic_vfadd_vv_nxv1f16_nxv1f16_nxv1f16(<vscale x 1 x half> %0, <vscale x 1 x half> %1, iXLen %2) nounwind {
 ; CHECK-LABEL: intrinsic_vfadd_vv_nxv1f16_nxv1f16_nxv1f16: