[PATCH 10/12] aarch64: Add aarch64_feature_flags_from_index macro

[Andrew Carlotti <andrew.carlotti@arm.com>]

When aarch64_feature_flags grows to 128 bits, constructing a mask with a
specific indexed value set will become more complicated.  Extract this
operation into a separate macro, and preemptively annotate the feature
masks as possibly unused.

gcc/ChangeLog:

	* config/aarch64/aarch64-opts.h
	(aarch64_feature_flags_from_index): New macro.
	* config/aarch64/aarch64.h
	(AARCH64_FL_##IDENT): Mark as maybe unused, and use new macro.


diff --git a/gcc/config/aarch64/aarch64-opts.h b/gcc/config/aarch64/aarch64-opts.h
index c2d68716857b49db8f9c1393f11b3377f51fb60c..80926a008aa2ed7dffa79aaa425dd3d7fc9d2581 100644
--- a/gcc/config/aarch64/aarch64-opts.h
+++ b/gcc/config/aarch64/aarch64-opts.h
@@ -32,6 +32,9 @@ constexpr unsigned int AARCH64_NUM_ISA_MODES = (0
 #include "aarch64-isa-modes.def"
 );
 
+#define aarch64_feature_flags_from_index(index) \
+  (aarch64_feature_flags (uint64_t (1) << index))
+
 #define AARCH64_NO_FEATURES aarch64_feature_flags (0)
 #endif
 
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index af256c581aedc04e4194ac0158380fcdb8b65594..dd3437214e1597f03ac947a09c124ea0b04e27e8 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -185,8 +185,8 @@ enum class aarch64_feature : unsigned char {
 
 /* Define unique flags for each of the above.  */
 #define HANDLE(IDENT) \
-  constexpr auto AARCH64_FL_##IDENT \
-    = aarch64_feature_flags (1) << int (aarch64_feature::IDENT);
+  constexpr auto AARCH64_FL_##IDENT ATTRIBUTE_UNUSED \
+    = aarch64_feature_flags_from_index (int (aarch64_feature::IDENT));
 #define DEF_AARCH64_ISA_MODE(IDENT) HANDLE (IDENT)
 #define AARCH64_OPT_EXTENSION(A, IDENT, C, D, E, F) HANDLE (IDENT)
 #define AARCH64_ARCH(A, B, IDENT, D, E) HANDLE (IDENT)