riscv64: Implement Riscv64InstructionSetFeatures::AddFeaturesFromSplitString

This only parses a subset of the ISA string format: the known extensions
in their canonical order, as generated by GetFeatureString. The ISA
string is assumed to be complete, so when present we ignore the existing
value of bits_.

To simplify future changes, reuse kExtensionList in GetFeatureString.

Test: m test-art-host-gtest-art_runtime_tests64
Change-Id: I0e9cd0423d9850d2b4f81c338743b82d488c4fa4

3 files changed, 59 insertions, 14 deletions

diff --git a/runtime/arch/riscv64/instruction_set_features_riscv64.cc b/runtime/arch/riscv64/instruction_set_features_riscv64.cc
index 7e5299dce4..947ea54ddb 100644
--- a/runtime/arch/riscv64/instruction_set_features_riscv64.cc
+++ b/runtime/arch/riscv64/instruction_set_features_riscv64.cc
@@ -19,11 +19,14 @@
 #include <fstream>
 #include <sstream>
 
+#include "android-base/stringprintf.h"
 #include "android-base/strings.h"
 #include "base/logging.h"
 
 namespace art {
 
+using android::base::StringPrintf;
+
 // Basic feature set is rv64gcv, aka rv64imafdcv.
 constexpr uint32_t BasicFeatures() {
   return Riscv64InstructionSetFeatures::kExtGeneric |
@@ -83,26 +86,44 @@ bool Riscv64InstructionSetFeatures::Equals(const InstructionSetFeatures* other)
 
 uint32_t Riscv64InstructionSetFeatures::AsBitmap() const { return bits_; }
 
+static const std::pair<uint32_t, std::string> kExtensionList[] = {
+    {Riscv64InstructionSetFeatures::kExtGeneric, "rv64g"},
+    {Riscv64InstructionSetFeatures::kExtCompressed, "c"},
+    {Riscv64InstructionSetFeatures::kExtVector, "v"},
+};
+
 std::string Riscv64InstructionSetFeatures::GetFeatureString() const {
-  std::string result = "rv64";
-  if (bits_ & kExtGeneric) {
-    result += "g";
-  }
-  if (bits_ & kExtCompressed) {
-    result += "c";
-  }
-  if (bits_ & kExtVector) {
-    result += "v";
+  std::string result = "";
+  for (auto&& [ext_bit, ext_string] : kExtensionList) {
+    if (bits_ & ext_bit) {
+      result += ext_string;
+    }
   }
   return result;
 }
 
 std::unique_ptr<const InstructionSetFeatures>
-Riscv64InstructionSetFeatures::AddFeaturesFromSplitString(
-    [[maybe_unused]] const std::vector<std::string>& features,
-    [[maybe_unused]] std::string* error_msg) const {
-  UNIMPLEMENTED(WARNING);
-  return std::unique_ptr<const InstructionSetFeatures>(new Riscv64InstructionSetFeatures(bits_));
+Riscv64InstructionSetFeatures::AddFeaturesFromSplitString(const std::vector<std::string>& features,
+                                                          std::string* error_msg) const {
+  uint32_t bits = bits_;
+  if (!features.empty()) {
+    // There should be only one feature, the ISA string.
+    DCHECK_EQ(features.size(), 1U);
+    std::string_view isa_string = features.front();
+    bits = 0;
+    for (auto&& [ext_bit, ext_string] : kExtensionList) {
+      if (isa_string.substr(0, ext_string.length()) == ext_string) {
+        isa_string.remove_prefix(ext_string.length());
+        bits |= ext_bit;
+      }
+    }
+    if (!isa_string.empty()) {
+      *error_msg = StringPrintf("Unknown extension in ISA string: '%s'", features.front().c_str());
+      return nullptr;
+    }
+    DCHECK(bits & kExtGeneric);
+  }
+  return FromBitmap(bits);
 }
 
 }  // namespace art
diff --git a/runtime/arch/riscv64/instruction_set_features_riscv64.h b/runtime/arch/riscv64/instruction_set_features_riscv64.h
index 1ad2ffd830..56c41f085b 100644
--- a/runtime/arch/riscv64/instruction_set_features_riscv64.h
+++ b/runtime/arch/riscv64/instruction_set_features_riscv64.h
@@ -67,6 +67,13 @@ class Riscv64InstructionSetFeatures final : public InstructionSetFeatures {
   virtual ~Riscv64InstructionSetFeatures() {}
 
  protected:
+  // If `features` is empty, this method doesn't add/remove anything from the
+  // existing set of features.
+  // If `features` is not empty, this method expects it to have exactly one value
+  // which is assumed to be a complete and valid features string. In this case, the
+  // new features will override the old ones. For example, if the existing set of
+  // features were `rv64gcv_zba_zbb_zbs` but `features` is `{"rv64gcv"}`, then the
+  // new features will not have the bits set for Zba, Zbb, or Zbs.
   std::unique_ptr<const InstructionSetFeatures> AddFeaturesFromSplitString(
       const std::vector<std::string>& features, std::string* error_msg) const override;
 
diff --git a/runtime/arch/riscv64/instruction_set_features_riscv64_test.cc b/runtime/arch/riscv64/instruction_set_features_riscv64_test.cc
index 0f0cbda8b7..fd9e83b81a 100644
--- a/runtime/arch/riscv64/instruction_set_features_riscv64_test.cc
+++ b/runtime/arch/riscv64/instruction_set_features_riscv64_test.cc
@@ -37,4 +37,21 @@ TEST(Riscv64InstructionSetFeaturesTest, Riscv64FeaturesFromDefaultVariant) {
   EXPECT_EQ(riscv64_features->AsBitmap(), expected_extensions);
 }
 
+TEST(Riscv64InstructionSetFeaturesTest, Riscv64FeaturesFromString) {
+  std::string error_msg;
+  std::unique_ptr<const InstructionSetFeatures> generic_features(
+      InstructionSetFeatures::FromVariant(InstructionSet::kRiscv64, "generic", &error_msg));
+  ASSERT_TRUE(generic_features.get() != nullptr) << error_msg;
+
+  std::unique_ptr<const InstructionSetFeatures> rv64gv_features(
+      generic_features->AddFeaturesFromString("rv64gv", &error_msg));
+  ASSERT_TRUE(rv64gv_features.get() != nullptr) << error_msg;
+
+  EXPECT_FALSE(generic_features->Equals(rv64gv_features.get()));
+
+  uint32_t expected_extensions = Riscv64InstructionSetFeatures::kExtGeneric |
+                                 Riscv64InstructionSetFeatures::kExtVector;
+  EXPECT_EQ(rv64gv_features->AsBitmap(), expected_extensions);
+}
+
 }  // namespace art