redo with isOperationLegalOrCustom

Change-Id: I4575a604fe5a76be2e657c63707c5fe25d631b98

Author: bojle

llvm/include/llvm/CodeGen/TargetLowering.h

@@ -3596,10 +3596,6 @@ class LLVM_ABI TargetLoweringBase {
     return false;
   }
 
-  /// Should usub.sat(X, 1) prefer the generic lowering X - zext(X != 0) over
-  /// the default overflow/select expansion?
-  virtual bool preferSubOfZextForUsubSatOne(EVT VT) const { return true; }
-
   /// True if target has some particular form of dealing with pointer arithmetic
   /// semantics for pointers with the given value type. False if pointer
   /// arithmetic should not be preserved for passes such as instruction

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -11475,8 +11475,9 @@ SDValue TargetLowering::expandAddSubSat(SDNode *Node, SelectionDAG &DAG) const {
   }
 
   // usub.sat(a, 1) -> sub(a, zext(a != 0))
+  // Prefer this on targets without legal/cost-effective overflow-carry nodes.
   if (Opcode == ISD::USUBSAT && isOneOrOneSplat(RHS) &&
-      preferSubOfZextForUsubSatOne(VT)) {
+      !isOperationLegalOrCustom(ISD::USUBO_CARRY, VT)) {
     LHS = DAG.getFreeze(LHS);
     SDValue Zero = DAG.getConstant(0, dl, VT);
     EVT BoolVT = getSetCCResultType(DAG.getDataLayout(), *DAG.getContext(), VT);

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -31035,11 +31035,6 @@ bool AArch64TargetLowering::shouldConvertFpToSat(unsigned Op, EVT FPVT,
   return TargetLowering::shouldConvertFpToSat(Op, FPVT, VT);
 }
 
-bool AArch64TargetLowering::preferSubOfZextForUsubSatOne(EVT /*VT*/) const {
-  // See https://github.com/llvm/llvm-project/issues/191488
-  return false;
-}
-
 bool AArch64TargetLowering::preferSelectsOverBooleanArithmetic(EVT VT) const {
   // Expand scalar and SVE operations using selects. Neon vectors prefer sub to
   // avoid vselect becoming bsl / unrolling.

llvm/lib/Target/AArch64/AArch64ISelLowering.h

@@ -450,8 +450,6 @@ class AArch64TargetLowering : public TargetLowering {
 
   bool shouldConvertFpToSat(unsigned Op, EVT FPVT, EVT VT) const override;
 
-  bool preferSubOfZextForUsubSatOne(EVT VT) const override;
-
   bool preferSelectsOverBooleanArithmetic(EVT VT) const override;
 
   bool isComplexDeinterleavingSupported() const override;