[llvm] [ARM] Add scalar add_sat costs. (PR #100988)

[David Green via llvm-commits]

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@@ -1904,17 +1905,37 @@ ARMTTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
   case Intrinsic::ssub_sat:
   case Intrinsic::uadd_sat:
   case Intrinsic::usub_sat: {
+    bool IsAdd = (Opc == Intrinsic::sadd_sat || Opc == Intrinsic::ssub_sat);
+    bool IsSigned = (Opc == Intrinsic::sadd_sat || Opc == Intrinsic::ssub_sat);
+    Type *RetTy = ICA.getReturnType();
+
+    if (RetTy->isIntegerTy()) {
+      if (IsSigned && ST->hasDSP() && RetTy->isIntegerTy(32))
+        return 1; // qadd / qsub
+      if (ST->hasDSP() && (RetTy->isIntegerTy(8) || RetTy->isIntegerTy(16)))
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davemgreen wrote:

They would need to emit the cmp+sel for saturating to the original type.

https://github.com/llvm/llvm-project/pull/100988