[ARM] Select fp16 fabs

[dmgreen]

Summary

Adds a pattern for the intrinsic, the same as float and double.

[SjoerdMeijer]

LGTM

llvm/lib/Target/ARM/ARMInstrVFP.td

def VABSS  : ASuIn<0b11101, 0b11, 0b0000, 0b11, 0,
                    IIC_fpUNA32, "vabs", ".f32\t$Sd, $Sm",
                    [(set SPR:$Sd, (fabs SPR:$Sm))]> {
   // Some single precision VFP instructions may be executed on both NEON and
   // VFP pipelines on A8.
   let D = VFPNeonA8Domain;
 }
 
 def VABSH  : AHuI<0b11101, 0b11, 0b0000, 0b11, 0,
-                   (outs SPR:$Sd), (ins SPR:$Sm),
+                   (outs HPR:$Sd), (ins HPR:$Sm),
                    IIC_fpUNA16, "vabs", ".f16\t$Sd, $Sm",
-                   []>;
+                   [(set HPR:$Sd, (fabs (f16 HPR:$Sm)))]>;
 
 let Defs = [FPSCR_NZCV] in {
 def VCMPEZD : ADuI<0b11101, 0b11, 0b0101, 0b11, 0,
                    (outs), (ins DPR:$Dd),
                    IIC_fpCMP64, "vcmpe", ".f64\t$Dd, #0",
                    [(arm_cmpfp0 (f64 DPR:$Dd), (i32 1))]> {
   let Inst{3-0} = 0b0000;
   let Inst{5}   = 0;

llvm/test/CodeGen/ARM/fp16-full.ll

 ;  %a = load half, half* %p, align 2
 ;  %b = load half, half* %q, align 2
 ;  %c = load half, half* %r, align 2
 ;  %v = call half @llvm.fma.f16(half %a, half %b, half %c)
 ;  store half %v, half* %p
 ;  ret void
 ;}
 
-; FIXME
-;define void @test_fabs(half* %p) {
-;  %a = load half, half* %p, align 2
-;  %r = call half @llvm.fabs.f16(half %a)
-;  store half %r, half* %p
-;  ret void
-;}
+define void @test_fabs(half* %p) {
+; CHECK-LABEL: test_fabs:
+; CHECK:         vldr.16 s0, [r0]
+; CHECK-NEXT:    vabs.f16 s0, s0
+; CHECK-NEXT:    vstr.16 s0, [r0]
+; CHECK-NEXT:    bx lr
+  %a = load half, half* %p, align 2
+  %r = call half @llvm.fabs.f16(half %a)
+  store half %r, half* %p
+  ret void
+}
 
 define void @test_minnum(half* %p, half* %q) {
 ; CHECK-LABEL: test_minnum:
 ; CHECK:         vldr.16 s0, [r1]
 ; CHECK-NEXT:    vldr.16 s2, [r0]
 ; CHECK-NEXT:    vminnm.f16 s0, s2, s0
 ; CHECK-NEXT:    vstr.16 s0, [r0]
 ; CHECK-NEXT:    bx lr