[CostModel][AArch64] Fix ctpop intrinsic cost when NEON is disabled.

[efriedma]

Summary

If we don't have NEON, we use the generic fallback, which takes 12 instructions. Make sure the costs reflect that.

(On a related note, we could optimize the generic fallback a bit. It currently uses sequences like lsr+and+add; if we use and+lsr+add instead, we can fold the lsr into the add. But I'm not planning to look into that at the moment.)

[dmgreen]

12 sounds good. LGTM

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

if (Entry) {
           TLI->getValueType(DL, RetTy, true) == MVT::i16)
         return LegalisationCost.first * Entry->Cost + 1;
 
       return LegalisationCost.first * Entry->Cost;
     }
     break;
   }
   case Intrinsic::ctpop: {
+    if (!ST->hasNEON()) {
+      // 32-bit or 64-bit ctpop without NEON is 12 instructions.
+      return getTypeLegalizationCost(RetTy).first * 12;
+    }
     static const CostTblEntry CtpopCostTbl[] = {
         {ISD::CTPOP, MVT::v2i64, 4},
         {ISD::CTPOP, MVT::v4i32, 3},
         {ISD::CTPOP, MVT::v8i16, 2},
         {ISD::CTPOP, MVT::v16i8, 1},
         {ISD::CTPOP, MVT::i64,   4},
         {ISD::CTPOP, MVT::v2i32, 3},
         {ISD::CTPOP, MVT::v4i16, 2},

llvm/test/Analysis/CostModel/AArch64/ctpop.ll

 define <32 x i8> @test_ctpop_v32i8(<32 x i8> %a) {
 ; CHECK-LABEL: 'test_ctpop_v32i8'
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %ctpop = call <32 x i8> @llvm.ctpop.v32i8(<32 x i8> %a)
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret <32 x i8> %ctpop
   %ctpop = call <32 x i8> @llvm.ctpop.v32i8(<32 x i8> %a)
   ret <32 x i8> %ctpop
 }
 
+define i64 @test_ctpop_noneon_i64(i64 %a) "target-features"="-fp-armv8,-neon" {
+; CHECK-LABEL: 'test_ctpop_noneon_i64'
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 12 for instruction: %ctpop = call i64 @llvm.ctpop.i64(i64 %a)
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret i64 %ctpop
+  %ctpop = call i64 @llvm.ctpop.i64(i64 %a)
+  ret i64 %ctpop
+}
+
+define <2 x i64> @test_ctpop_noneon_v2i64(<2 x i64> %a) "target-features"="-fp-armv8,-neon" {
+; CHECK-LABEL: 'test_ctpop_noneon_v2i64'
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 24 for instruction: %ctpop = call <2 x i64> @llvm.ctpop.v2i64(<2 x i64> %a)
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret <2 x i64> %ctpop
+  %ctpop = call <2 x i64> @llvm.ctpop.v2i64(<2 x i64> %a)
+  ret <2 x i64> %ctpop
+}
+
 declare <2 x i64> @llvm.ctpop.v2i64(<2 x i64>)
 declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32>)
 declare <4 x i32> @llvm.ctpop.v4i32(<4 x i32>)
 declare <2 x i16> @llvm.ctpop.v2i16(<2 x i16>)
 declare <4 x i16> @llvm.ctpop.v4i16(<4 x i16>)
 declare <8 x i16> @llvm.ctpop.v8i16(<8 x i16>)
 declare <2 x i8> @llvm.ctpop.v2i8(<2 x i8>)
 declare <4 x i8> @llvm.ctpop.v4i8(<4 x i8>)
 declare <8 x i8> @llvm.ctpop.v8i8(<8 x i8>)
 declare <16 x i8> @llvm.ctpop.v16i8(<16 x i8>)
 
 declare <4 x i64> @llvm.ctpop.v4i64(<4 x i64>)
 declare <8 x i32> @llvm.ctpop.v8i32(<8 x i32>)
 declare <16 x i16> @llvm.ctpop.v16i16(<16 x i16>)
 declare <32 x i8> @llvm.ctpop.v32i8(<32 x i8>)