[TTI] Provide a cost for memset_pattern which matches the libcall

The motivation is that differences in unrolling were noticed when
trying to swich from the libcall to the intrinsic.  Neither cost
is a good, well considered cost, but for the moment, let's have
them be equal to simplify migration.

Author: preames

llvm/include/llvm/CodeGen/BasicTTIImpl.h

@@ -2408,6 +2408,9 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
                                           CmpInst::ICMP_ULT, CostKind);
       return Cost;
     }
+    case Intrinsic::experimental_memset_pattern:
+      // This cost is set to match the cost of the memset_pattern16 libcall
+      return TTI::TCC_Basic * 4;
     case Intrinsic::abs:
       ISD = ISD::ABS;
       break;

llvm/test/Analysis/CostModel/X86/memset-pattern.ll

@@ -26,10 +26,10 @@ declare void @memset_pattern16(ptr, ptr, i64)
 
 define void @via_intrinsic(ptr %p) {
 ; CHECK-LABEL: 'via_intrinsic'
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: call void @llvm.experimental.memset.pattern.p0.i16.i64(ptr align 4 %p, i16 2, i64 100, i1 false)
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: call void @llvm.experimental.memset.pattern.p0.i32.i64(ptr align 4 %p, i32 2, i64 50, i1 false)
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: call void @llvm.experimental.memset.pattern.p0.i64.i64(ptr align 4 %p, i64 2, i64 25, i1 false)
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: call void @llvm.experimental.memset.pattern.p0.i128.i64(ptr align 4 %p, i128 2, i64 12, i1 false)
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: call void @llvm.experimental.memset.pattern.p0.i16.i64(ptr align 4 %p, i16 2, i64 100, i1 false)
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: call void @llvm.experimental.memset.pattern.p0.i32.i64(ptr align 4 %p, i32 2, i64 50, i1 false)
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: call void @llvm.experimental.memset.pattern.p0.i64.i64(ptr align 4 %p, i64 2, i64 25, i1 false)
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: call void @llvm.experimental.memset.pattern.p0.i128.i64(ptr align 4 %p, i128 2, i64 12, i1 false)
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;
   call void @llvm.experimental.memset.pattern(ptr align 4 %p, i16 2, i64 100, i1 false)