[SelectionDAG][SVE] Support scalable vectors in getConstantFP()

[sdesmalen]

Nice, LGTM!

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

SDValue SelectionDAG::getConstantFP(const ConstantFP &V, const SDLoc &DL,
 
   if (!N) {
     N = newSDNode<ConstantFPSDNode>(isTarget, &V, EltVT);
     CSEMap.InsertNode(N, IP);
     InsertNode(N);
   }
 
   SDValue Result(N, 0);
-  if (VT.isVector())
+  if (VT.isScalableVector())
+    Result = getSplatVector(VT, DL, Result);
+  else if (VT.isVector())
     Result = getSplatBuildVector(VT, DL, Result);
   NewSDValueDbgMsg(Result, "Creating fp constant: ", this);
   return Result;
 }
 
 SDValue SelectionDAG::getConstantFP(double Val, const SDLoc &DL, EVT VT,
                                     bool isTarget) {
   EVT EltVT = VT.getScalarType();

llvm/test/CodeGen/AArch64/sve-vector-splat.ll

 ; CHECK-LABEL: splat_nxv2f64_imm:
 ; CHECK: mov z0.d, #1.0
 ; CHECK-NEXT: ret
   %1 = insertelement <vscale x 2 x double> undef, double 1.0, i32 0
   %2 = shufflevector <vscale x 2 x double> %1, <vscale x 2 x double> undef, <vscale x 2 x i32> zeroinitializer
   ret <vscale x 2 x double> %2
 }
 
+define <vscale x 4 x i32> @splat_nxv4i32_fold(<vscale x 4 x i32> %x) {
+; CHECK-LABEL: splat_nxv4i32_fold:
+; CHECK: mov z0.s, #0
+; CHECK-NEXT: ret
+  %r = sub <vscale x 4 x i32> %x, %x
+  ret <vscale x 4 x i32> %r
+}
+
+
+define <vscale x 4 x float> @splat_nxv4f32_fold(<vscale x 4 x float> %x) {
+; CHECK-LABEL: splat_nxv4f32_fold:
+; CHECK: mov z0.s, #0
+; CHECK-NEXT: ret
+  %r = fsub nnan <vscale x 4 x float> %x, %x
+  ret <vscale x 4 x float> %r
+}
+
 ; +bf16 is required for the bfloat version.
 attributes #0 = { "target-features"="+sve,+bf16" }