diff --git a/library/common.h b/library/common.h
index f392b7f..c20f6b2 100644
--- a/library/common.h
+++ b/library/common.h
@@ -294,18 +294,36 @@
 #define MBEDTLS_STATIC_ASSERT(expr, msg)
 #endif
 
-/* Define compiler branch hints */
 #if defined(__has_builtin)
-#if __has_builtin(__builtin_expect)
+#define MBEDTLS_HAS_BUILTIN(x) __has_builtin(x)
+#else
+#define MBEDTLS_HAS_BUILTIN(x) 0
+#endif
+
+/* Define compiler branch hints */
+#if MBEDTLS_HAS_BUILTIN(__builtin_expect)
 #define MBEDTLS_LIKELY(x)       __builtin_expect(!!(x), 1)
 #define MBEDTLS_UNLIKELY(x)     __builtin_expect(!!(x), 0)
-#endif
-#endif
-#if !defined(MBEDTLS_LIKELY)
+#else
 #define MBEDTLS_LIKELY(x)       x
 #define MBEDTLS_UNLIKELY(x)     x
 #endif
 
+/* MBEDTLS_ASSUME may be used to provide additional information to the compiler
+ * which can result in smaller code-size. */
+#if MBEDTLS_HAS_BUILTIN(__builtin_assume)
+/* clang provides __builtin_assume */
+#define MBEDTLS_ASSUME(x)       __builtin_assume(x)
+#elif MBEDTLS_HAS_BUILTIN(__builtin_unreachable)
+/* gcc and IAR can use __builtin_unreachable */
+#define MBEDTLS_ASSUME(x)       do { if (!(x)) __builtin_unreachable(); } while (0)
+#elif defined(_MSC_VER)
+/* Supported by MSVC since VS 2005 */
+#define MBEDTLS_ASSUME(x)       __assume(x)
+#else
+#define MBEDTLS_ASSUME(x)       do { } while (0)
+#endif
+
 #if defined(__GNUC__) && !defined(__ARMCC_VERSION) && !defined(__clang__) \
     && !defined(__llvm__) && !defined(__INTEL_COMPILER)
 /* Defined if the compiler really is gcc and not clang, etc */
diff --git a/library/psa_crypto_cipher.c b/library/psa_crypto_cipher.c
index f0bb3aa..3132854 100644
--- a/library/psa_crypto_cipher.c
+++ b/library/psa_crypto_cipher.c
@@ -30,45 +30,97 @@
     psa_algorithm_t alg,
     psa_key_type_t key_type)
 {
-    switch (alg) {
-        case PSA_ALG_STREAM_CIPHER:
-        case PSA_ALG_AEAD_WITH_SHORTENED_TAG(PSA_ALG_CHACHA20_POLY1305, 0):
-            if (key_type != PSA_KEY_TYPE_CHACHA20) {
-                return PSA_ERROR_NOT_SUPPORTED;
-            }
-            break;
+    /* Reduce code size - hinting to the compiler about what it can assume allows the compiler to
+       eliminate bits of the logic below. */
+#if !defined(PSA_WANT_KEY_TYPE_AES)
+    MBEDTLS_ASSUME(key_type != PSA_KEY_TYPE_AES);
+#endif
+#if !defined(PSA_WANT_KEY_TYPE_ARIA)
+    MBEDTLS_ASSUME(key_type != PSA_KEY_TYPE_ARIA);
+#endif
+#if !defined(PSA_WANT_KEY_TYPE_CAMELLIA)
+    MBEDTLS_ASSUME(key_type != PSA_KEY_TYPE_CAMELLIA);
+#endif
+#if !defined(PSA_WANT_KEY_TYPE_CHACHA20)
+    MBEDTLS_ASSUME(key_type != PSA_KEY_TYPE_CHACHA20);
+#endif
+#if !defined(PSA_WANT_KEY_TYPE_DES)
+    MBEDTLS_ASSUME(key_type != PSA_KEY_TYPE_DES);
+#endif
+#if !defined(PSA_WANT_ALG_CCM)
+    MBEDTLS_ASSUME(alg != PSA_ALG_AEAD_WITH_SHORTENED_TAG(PSA_ALG_CCM, 0));
+#endif
+#if !defined(PSA_WANT_ALG_GCM)
+    MBEDTLS_ASSUME(alg != PSA_ALG_AEAD_WITH_SHORTENED_TAG(PSA_ALG_GCM, 0));
+#endif
+#if !defined(PSA_WANT_ALG_STREAM_CIPHER)
+    MBEDTLS_ASSUME(alg != PSA_ALG_STREAM_CIPHER);
+#endif
+#if !defined(PSA_WANT_ALG_CHACHA20_POLY1305)
+    MBEDTLS_ASSUME(alg != PSA_ALG_AEAD_WITH_SHORTENED_TAG(PSA_ALG_CHACHA20_POLY1305, 0));
+#endif
+#if !defined(PSA_WANT_ALG_CCM_STAR_NO_TAG)
+    MBEDTLS_ASSUME(alg != PSA_ALG_CCM_STAR_NO_TAG);
+#endif
+#if !defined(PSA_WANT_ALG_CTR)
+    MBEDTLS_ASSUME(alg != PSA_ALG_CTR);
+#endif
+#if !defined(PSA_WANT_ALG_CFB)
+    MBEDTLS_ASSUME(alg != PSA_ALG_CFB);
+#endif
+#if !defined(PSA_WANT_ALG_OFB)
+    MBEDTLS_ASSUME(alg != PSA_ALG_OFB);
+#endif
+#if !defined(PSA_WANT_ALG_XTS)
+    MBEDTLS_ASSUME(alg != PSA_ALG_XTS);
+#endif
+#if !defined(PSA_WANT_ALG_ECB_NO_PADDING)
+    MBEDTLS_ASSUME(alg != PSA_ALG_ECB_NO_PADDING);
+#endif
+#if !defined(PSA_WANT_ALG_CBC_NO_PADDING)
+    MBEDTLS_ASSUME(alg != PSA_ALG_CBC_NO_PADDING);
+#endif
+#if !defined(PSA_WANT_ALG_CBC_PKCS7)
+    MBEDTLS_ASSUME(alg != PSA_ALG_CBC_PKCS7);
+#endif
+#if !defined(PSA_WANT_ALG_CMAC)
+    MBEDTLS_ASSUME(alg != PSA_ALG_CMAC);
+#endif
 
-        case PSA_ALG_AEAD_WITH_SHORTENED_TAG(PSA_ALG_CCM, 0):
-        case PSA_ALG_AEAD_WITH_SHORTENED_TAG(PSA_ALG_GCM, 0):
-        case PSA_ALG_CCM_STAR_NO_TAG:
-            if ((key_type != PSA_KEY_TYPE_AES) &&
-                (key_type != PSA_KEY_TYPE_ARIA) &&
-                (key_type != PSA_KEY_TYPE_CAMELLIA)) {
-                return PSA_ERROR_NOT_SUPPORTED;
-            }
-            break;
-
-        case PSA_ALG_CTR:
-        case PSA_ALG_CFB:
-        case PSA_ALG_OFB:
-        case PSA_ALG_XTS:
-        case PSA_ALG_ECB_NO_PADDING:
-        case PSA_ALG_CBC_NO_PADDING:
-        case PSA_ALG_CBC_PKCS7:
-        case PSA_ALG_CMAC:
-            if ((key_type != PSA_KEY_TYPE_AES) &&
-                (key_type != PSA_KEY_TYPE_ARIA) &&
-                (key_type != PSA_KEY_TYPE_DES) &&
-                (key_type != PSA_KEY_TYPE_CAMELLIA)) {
-                return PSA_ERROR_NOT_SUPPORTED;
-            }
-            break;
-
-        default:
-            return PSA_ERROR_NOT_SUPPORTED;
+    if (alg == PSA_ALG_STREAM_CIPHER ||
+        alg == PSA_ALG_AEAD_WITH_SHORTENED_TAG(PSA_ALG_CHACHA20_POLY1305, 0)) {
+        if (key_type == PSA_KEY_TYPE_CHACHA20) {
+            return PSA_SUCCESS;
+        }
     }
 
-    return PSA_SUCCESS;
+    if (alg == PSA_ALG_AEAD_WITH_SHORTENED_TAG(PSA_ALG_CCM, 0) ||
+        alg == PSA_ALG_AEAD_WITH_SHORTENED_TAG(PSA_ALG_GCM, 0) ||
+        alg == PSA_ALG_CCM_STAR_NO_TAG) {
+        if (key_type == PSA_KEY_TYPE_AES ||
+            key_type == PSA_KEY_TYPE_ARIA ||
+            key_type == PSA_KEY_TYPE_CAMELLIA) {
+            return PSA_SUCCESS;
+        }
+    }
+
+    if (alg == PSA_ALG_CTR ||
+        alg == PSA_ALG_CFB ||
+        alg == PSA_ALG_OFB ||
+        alg == PSA_ALG_XTS ||
+        alg == PSA_ALG_ECB_NO_PADDING ||
+        alg == PSA_ALG_CBC_NO_PADDING ||
+        alg == PSA_ALG_CBC_PKCS7 ||
+        alg == PSA_ALG_CMAC) {
+        if (key_type == PSA_KEY_TYPE_AES ||
+            key_type == PSA_KEY_TYPE_ARIA ||
+            key_type == PSA_KEY_TYPE_DES ||
+            key_type == PSA_KEY_TYPE_CAMELLIA) {
+            return PSA_SUCCESS;
+        }
+    }
+
+    return PSA_ERROR_NOT_SUPPORTED;
 }
 
 psa_status_t mbedtls_cipher_values_from_psa(