tests: add an test to check the optimization result of a reverse-array function.

This is an end-to-end test to check if the optimization improvements of the previous commits result in good code generation for this function.

rdar://83825776
https://bugs.swift.org/browse/SR-15259

Author: eeckstein

test/SILOptimizer/reverse-array.swift

@@ -0,0 +1,68 @@
+// RUN: %target-swift-frontend  -primary-file %s -O -module-name=test -emit-sil | %FileCheck %s
+// RUN: %target-swift-frontend  -primary-file %s -O -module-name=test -emit-ir | %FileCheck %s -check-prefix=CHECK-LLVM
+
+// Also do an end-to-end test to check all components, including IRGen.
+// RUN: %empty-directory(%t) 
+// RUN: %target-build-swift -O -module-name=test %s -o %t/a.out
+// RUN: %target-run %t/a.out | %FileCheck %s -check-prefix=CHECK-OUTPUT
+
+// REQUIRES: libswift,executable_test,swift_stdlib_no_asserts,optimized_stdlib
+
+// Check that we create reasonable optimized code for this function.
+
+@inline(never)
+public func reverseArray(_ a: [Int]) -> [Int] {
+  var new: [Int] = []
+  new.reserveCapacity(a.count)
+
+  var fromIndex = a.count &- 1
+
+  while fromIndex >= 0 {
+    new.append(a[fromIndex])
+    fromIndex &-= 1
+  }
+
+  return new
+}
+
+
+// CHECK-LABEL: sil [noinline] @$s4test12reverseArrayySaySiGACF
+
+// There must not be more than two begin_cow_mutation - end_cow_mutation pairs:
+// * the first one for the initial reserveCapacity
+// * the second for the append.
+
+// CHECK-NOT: {{.*(_cow_mutation|cond_fail)}}
+// CHECK:     begin_cow_mutation
+// CHECK-NOT: {{.*(_cow_mutation|cond_fail)}}
+// CHECK:     end_cow_mutation
+// CHECK-NOT: {{.*(_cow_mutation|cond_fail)}}
+
+// In SIL we fail to eliminate the bounds check of the input array.
+// But that's okay, because LLVM can do that.
+// So we accept one cond_fail in the SIL output.
+
+// CHECK:     cond_fail {{.*}} "Index out of range"
+
+// The second begin_cow_mutation - end_cow_mutation pair:
+
+// CHECK-NOT: {{.*(_cow_mutation|cond_fail)}}
+// CHECK:     begin_cow_mutation
+// CHECK-NOT: {{.*(_cow_mutation|cond_fail)}}
+// CHECK:     end_cow_mutation
+// CHECK-NOT: {{.*(_cow_mutation|cond_fail)}}
+
+// CHECK: } // end sil function '$s4test12reverseArrayySaySiGACF'
+
+
+// Check that there are no cond_fails left in the LLVM output.
+// LLVM should be able to optimize away the bounds check of the input array.
+
+// CHECK-LLVM-LABEL: define {{.*}} @"$s4test12reverseArrayySaySiGACF"
+// CHECK-LLVM-NOT:     llvm.trap
+// CHECK-LLVM:       }
+
+
+// CHECK-OUTPUT: [3, 2, 1]
+print(reverseArray([1, 2, 3]))
+