[ARM] Fix select_cc lowering for fp16

When lowering a select_cc node where the true and false values are of type f16,
we can't use a general conditional move because the FP16 instructions do not
support conditional execution. Instead, we must ensure that the condition code
is one of the four supported by the VSEL instruction.

Differential revision: https://reviews.llvm.org/D58813

llvm-svn: 355385

llvm/lib/Target/ARM/ARMISelLowering.cpp

@@ -4494,7 +4494,8 @@ SDValue ARMTargetLowering::LowerSELECT_CC(SDValue Op, SelectionDAG &DAG) const {
     // inverting the compare condition, swapping 'less' and 'greater') and
     // sometimes need to swap the operands to the VSEL (which inverts the
     // condition in the sense of firing whenever the previous condition didn't)
-    if (Subtarget->hasFPARMv8() && (TrueVal.getValueType() == MVT::f32 ||
+    if (Subtarget->hasFPARMv8() && (TrueVal.getValueType() == MVT::f16 ||
+                                    TrueVal.getValueType() == MVT::f32 ||
                                     TrueVal.getValueType() == MVT::f64)) {
       ARMCC::CondCodes CondCode = IntCCToARMCC(CC);
       if (CondCode == ARMCC::LT || CondCode == ARMCC::LE ||
@@ -4514,12 +4515,15 @@ SDValue ARMTargetLowering::LowerSELECT_CC(SDValue Op, SelectionDAG &DAG) const {
   bool InvalidOnQNaN;
   FPCCToARMCC(CC, CondCode, CondCode2, InvalidOnQNaN);
 
-  // Normalize the fp compare. If RHS is zero we keep it there so we match
-  // CMPFPw0 instead of CMPFP.
-  if (Subtarget->hasFPARMv8() && !isFloatingPointZero(RHS) &&
-     (TrueVal.getValueType() == MVT::f16 ||
-      TrueVal.getValueType() == MVT::f32 ||
-      TrueVal.getValueType() == MVT::f64)) {
+  // Normalize the fp compare. If RHS is zero we prefer to keep it there so we
+  // match CMPFPw0 instead of CMPFP, though we don't do this for f16 because we
+  // must use VSEL (limited condition codes), due to not having conditional f16
+  // moves.
+  if (Subtarget->hasFPARMv8() &&
+      !(isFloatingPointZero(RHS) && TrueVal.getValueType() != MVT::f16) &&
+      (TrueVal.getValueType() == MVT::f16 ||
+       TrueVal.getValueType() == MVT::f32 ||
+       TrueVal.getValueType() == MVT::f64)) {
     bool swpCmpOps = false;
     bool swpVselOps = false;
     checkVSELConstraints(CC, CondCode, swpCmpOps, swpVselOps);