benchmarks: Remove the StackPromo benchmark and make it a lit test

This benchmark just wants to test if stack promotion of an array literal works.
This is so simple that it's better tested with a lit test.

Author: eeckstein

benchmark/CMakeLists.txt

@@ -181,7 +181,6 @@ set(SWIFT_BENCH_MODULES
     single-source/SortLargeExistentials
     single-source/SortLettersInPlace
     single-source/SortStrings
-    single-source/StackPromo
     single-source/StaticArray
     single-source/StrComplexWalk
     single-source/StrToInt

benchmark/single-source/StackPromo.swift

@@ -186,7 +186,6 @@ import SortIntPyramids
 import SortLargeExistentials
 import SortLettersInPlace
 import SortStrings
-import StackPromo
 import StaticArray
 import StrComplexWalk
 import StrToInt
@@ -388,7 +387,6 @@ register(SortIntPyramids.benchmarks)
 register(SortLargeExistentials.benchmarks)
 register(SortLettersInPlace.benchmarks)
 register(SortStrings.benchmarks)
-register(StackPromo.benchmarks)
 register(StaticArray.benchmarks)
 register(StrComplexWalk.benchmarks)
 register(StrToInt.benchmarks)

benchmark/utils/main.swift

@@ -6,9 +6,9 @@
 // This is an end-to-end test to check if the array literal in the loop is
 // stack promoted.
 
-// CHECK-LABEL: sil @{{.*}}testit
-// CHECK:  alloc_ref{{.*}} [stack] [tail_elems
-
+// CHECK-LABEL: sil @$s4test6testityySi_SitF :
+// CHECK:         alloc_ref{{.*}} [stack] [tail_elems
+// CHECK:       } // end sil function '$s4test6testityySi_SitF'
 public func testit(_ N: Int, _ x: Int) {
   for _ in 0..<N {
     for _ in 0..<10 {
@@ -19,3 +19,28 @@ public func testit(_ N: Int, _ x: Int) {
     }
   }
 }
+
+public protocol Proto {
+  func at() -> Int
+}
+
+// CHECK-LABEL: sil @$s4test5test2ySiAA5Proto_pF :
+// CHECK:         alloc_ref{{.*}} [stack] [tail_elems $any Proto
+// CHECK:         br bb1
+// CHECK:       bb1({{.*}}):
+// CHECK:         [[M:%.*]] = witness_method
+// CHECK:         apply [[M]]
+// CHECK:         cond_br
+// CHECK:       bb2:
+// CHECK:       } // end sil function '$s4test5test2ySiAA5Proto_pF'
+public func test2(_ p: Proto) -> Int {
+  var a = [p, p, p]
+  var b = 0
+  a.withUnsafeMutableBufferPointer {
+    let array = $0
+    for i in 0..<array.count {
+      b += array[i].at()
+    }
+  }
+  return b
+}