[embedded] Avoid unsafeBitCast, use Builtin.castFromNativeObject instead, add armv7 test

Author: kubamracek

stdlib/public/core/StringObject.swift

@@ -983,7 +983,7 @@ extension _StringObject {
     #if !$Embedded
     return _unsafeUncheckedDowncast(storage, to: __StringStorage.self)
     #else
-    return unsafeBitCast(_nativeObject(toNative: storage), to: __StringStorage.self)
+    return Builtin.castFromNativeObject(storage)
     #endif
 #else
 #error("Unknown platform")
@@ -1022,7 +1022,7 @@ extension _StringObject {
     #if !$Embedded
     return _unsafeUncheckedDowncast(storage, to: __SharedStringStorage.self)
     #else
-    return unsafeBitCast(_nativeObject(toNative: storage), to: __SharedStringStorage.self)
+    return Builtin.castFromNativeObject(storage)
     #endif
 #else
 #error("Unknown platform")

test/embedded/stdlib-strings-interpolation3.swift

@@ -0,0 +1,31 @@
+// RUN: %target-swift-frontend -target armv7-apple-none-macho -module-name main -parse-as-library -Xcc -D__MACH__ -emit-ir %s -enable-experimental-feature Embedded
+// RUN: %target-swift-frontend -target armv7-apple-none-macho -module-name main -parse-as-library -Xcc -D__MACH__ -emit-ir %s -enable-experimental-feature Embedded -O
+// RUN: %target-swift-frontend -target armv7-apple-none-macho -module-name main -parse-as-library -Xcc -D__MACH__ -emit-ir %s -enable-experimental-feature Embedded -Osize
+
+// REQUIRES: swift_in_compiler
+// REQUIRES: OS=macosx || OS=linux-gnu
+// REQUIRES: CODEGENERATOR=ARM
+
+@main
+struct Main {
+  static func main() {
+    let n = 42
+    let m = -42
+    let s = "str"
+    let str = "Hello \(s) \(n) \(s) \(m)"
+    print(str)
+
+    print("hex: \(hex: 42)")
+    print("ptr: \(UnsafeRawPointer(bitPattern: UInt(0xffff0000))!)")
+  }
+}
+
+extension DefaultStringInterpolation {
+  mutating func appendInterpolation(hex value: Int) {
+    appendInterpolation("0x" + String(value, radix: 16))
+  }
+
+  mutating func appendInterpolation(_ value: UnsafeRawPointer) {
+    appendInterpolation("0x" + String(UInt(bitPattern: value), radix: 16))
+  }
+}