Add known instruction set variants to logging strings

If a user had a wrong variant, they would get a message like
`Unexpected CPU variant for X86 using defaults: x86` but they
wouldn't know which ones we accept, unless they take a look at
the code.

This change comes after a developer's suggestion when encountering
said warning string.

Test: Presubmit tests
Change-Id: I3a7b9408cf55114229843f6ff6013999350d7185

1 files changed, 10 insertions, 0 deletions

diff --git a/runtime/arch/instruction_set_features.cc b/runtime/arch/instruction_set_features.cc
index ec1e340245..5ae920bef1 100644
--- a/runtime/arch/instruction_set_features.cc
+++ b/runtime/arch/instruction_set_features.cc
@@ -267,6 +267,16 @@ bool InstructionSetFeatures::FindVariantInArray(const char* const variants[], si
   return std::find(begin, end, variant) != end;
 }
 
+void InstructionSetFeatures::CommaSeparateVariants(std::ostream& os,
+                                                   const char* const variants[],
+                                                   size_t num_variants) {
+  std::string separator = "";
+  for (size_t i = 0u; i < num_variants; ++i) {
+    os << separator << variants[i];
+    separator = ", ";
+  }
+}
+
 std::unique_ptr<const InstructionSetFeatures> InstructionSetFeatures::AddRuntimeDetectedFeatures(
     const InstructionSetFeatures *features ATTRIBUTE_UNUSED) const {
   UNIMPLEMENTED(FATAL) << kRuntimeISA;