Merge pull request #34995 from zoecarver/tests/witness-table-opts

[nfc] Add tests for witness table size optimizations.

Author: zoecarver

test/Interop/Cxx/value-witness-table/Inputs/module.modulemap

@@ -2,3 +2,8 @@ module CustomDestructor {
   header "custom-destructors.h"
   requires cplusplus
 }
+
+module WitnessLayoutOpts {
+  header "witness-layout-opts.h"
+  requires cplusplus
+}

test/Interop/Cxx/value-witness-table/Inputs/witness-layout-opts.h

@@ -0,0 +1,10 @@
+#ifndef TEST_INTEROP_CXX_VALUE_WITNESS_TABLE_INPUTS_WITNESS_LAYOUT_H
+#define TEST_INTEROP_CXX_VALUE_WITNESS_TABLE_INPUTS_WITNESS_LAYOUT_H
+
+struct Empty { };
+
+struct I8Size { char value; };
+
+struct I32Size { char value[3]; char other; };
+
+#endif // TEST_INTEROP_CXX_VALUE_WITNESS_TABLE_INPUTS_WITNESS_LAYOUT_H

test/Interop/Cxx/value-witness-table/witness-layout-opts-irgen.swift

@@ -0,0 +1,24 @@
+// RUN: %target-swift-emit-ir %s -I %S/Inputs -enable-cxx-interop | %FileCheck %s
+
+// This test checks that the compiler uses well-known witness tables for types
+// that have the appropriate size/shape (for example, { i8 x 4 } -> i32).
+
+// These witness tables look very differnt on Windows so it doesn't make sense
+// to test them in the same file.
+// XFAIL: OS=windows-msvc
+
+import WitnessLayoutOpts
+
+protocol Dummy { }
+
+// CHECK-DAG: @"$sBi8_WV" = external global i8*, align 8
+// CHECK-DAG: @"$sSo5EmptyVMf" = linkonce_odr hidden constant {{.*}}@"$sBi8_WV"
+
+extension Empty : Dummy { }
+
+// CHECK-DAG: @"$sSo6I8SizeVMf" = linkonce_odr hidden constant {{.*}}@"$sBi8_WV"
+extension I8Size : Dummy { }
+
+// CHECK-DAG: @"$sSo7I32SizeVWV" = linkonce_odr hidden constant %swift.vwtable { {{.*}} i8* bitcast (i32 (%swift.opaque*, i32, %swift.type*)* @"$sSo7I32SizeVwet" to i8*), i8* bitcast (void (%swift.opaque*, i32, i32, %swift.type*)* @"$sSo7I32SizeVwst" to i8*)
+// CHECK-DAG: "$sSo7I32SizeVMf" = linkonce_odr hidden constant {{.*}}@"$sSo7I32SizeVWV"
+extension I32Size : Dummy { }