[slightly revise]

Author: kinke

CHANGELOG.md

@@ -7,7 +7,7 @@
 
 #### Platform support
 - Supports LLVM 11.0 - 16.0.
-- When nothing else specified now defaults to `-mattr=+m,+a,+f,+d,+c` when targeting hosted 64-bit RISC-V. (#4390)
+- 64-bit RISC-V: Now defaults to `-mattr=+m,+a,+f,+d,+c` ('rv64gc' ABI) for non-bare-metal targets, i.e., if the target triple includes a valid operating system. (#4390)
 
 #### Bug fixes
 - Fix function pointers/delegates on Harvard architectures (e.g., AVR). (#4432, #4465)

driver/targetmachine.cpp

@@ -57,7 +57,20 @@ static llvm::cl::opt<bool, true> preserveDwarfLineSection(
     llvm::cl::init(false));
 #endif
 
-const char *getABI(const llvm::Triple &triple, const llvm::SmallVector<llvm::StringRef, 8> &features) {
+// Returns true if 'feature' is enabled and false otherwise. Handles the
+// case where the feature is specified multiple times ('+m,-m'), and
+// takes the last occurrence.
+bool isFeatureEnabled(const llvm::SmallVectorImpl<llvm::StringRef> &features,
+                      llvm::StringRef feature) {
+  for (auto it = features.rbegin(), end = features.rend(); it != end; ++it) {
+    if (it->substr(1) == feature) {
+      return (*it)[0] == '+';
+    }
+  }
+  return false;
+};
+
+const char *getABI(const llvm::Triple &triple, const llvm::SmallVectorImpl<llvm::StringRef> &features) {
   llvm::StringRef ABIName(opts::mABI);
   if (ABIName != "") {
     switch (triple.getArch()) {
@@ -111,17 +124,6 @@ const char *getABI(const llvm::Triple &triple, const llvm::SmallVector<llvm::Str
             ABIName.str().c_str());
   }
 
-  // checks if the features include ±<feature>
-  auto hasFeature = [&features](llvm::StringRef feature) {
-    for (int i = features.size() - 1; i >= 0; i--) {
-      auto f = features[i];
-      if (f.substr(1) == feature) {
-	return f[0] == '+';
-      }
-    }
-    return false;
-  };
-
   switch (triple.getArch()) {
   case llvm::Triple::mips64:
   case llvm::Triple::mips64el:
@@ -131,9 +133,9 @@ const char *getABI(const llvm::Triple &triple, const llvm::SmallVector<llvm::Str
   case llvm::Triple::ppc64le:
     return "elfv2";
   case llvm::Triple::riscv64:
-    if (hasFeature("d"))
+    if (isFeatureEnabled(features, "d"))
       return "lp64d";
-    if (hasFeature("f"))
+    if (isFeatureEnabled(features, "f"))
       return "lp64f";
     return "lp64";
   case llvm::Triple::riscv32:
@@ -445,13 +447,9 @@ createTargetMachine(const std::string targetTriple, const std::string arch,
 
   // checks if the features include ±<feature>
   auto hasFeature = [&features](llvm::StringRef feature) {
-    for (int i = features.size() - 1; i >= 0; i--) {
-      auto f = features[i];
-      if (f.substr(1) == feature) {
-	return f[0] == '+';
-      }
-    }
-    return false;
+    return std::any_of(
+        features.begin(), features.end(),
+        [feature](llvm::StringRef f) { return f.substr(1) == feature; });
   };
 
   // cmpxchg16b is not available on old 64bit CPUs. Enable code generation
@@ -462,14 +460,12 @@ createTargetMachine(const std::string targetTriple, const std::string arch,
 
   // For a hosted RISC-V 64-bit target default to rv64gc if nothing has
   // been selected
-  if (triple.getArch() == llvm::Triple::riscv64 &&
-      triple.getOS() != llvm::Triple::UnknownOS &&
-      features.empty()) {
-    features.push_back("+m");
-    features.push_back("+a");
-    features.push_back("+f");
-    features.push_back("+d");
-    features.push_back("+c");
+  if (triple.getArch() == llvm::Triple::riscv64 && features.empty()) {
+    const llvm::StringRef os = triple.getOSName();
+    const bool isFreeStanding = os.empty() || os == "unknown" || os == "none";
+    if (!isFreeStanding) {
+      features = {"+m", "+a", "+f", "+d", "+c"};
+    }
   }
 
   // Handle cases where LLVM picks wrong default relocModel

driver/targetmachine.h

@@ -76,4 +76,7 @@ const llvm::Target *lookupTarget(const std::string &arch, llvm::Triple &triple,
                                  std::string &errorMsg);
 
 const char *getABI(const llvm::Triple &triple,
-		   const llvm::SmallVector<llvm::StringRef, 8> &features);
+                   const llvm::SmallVectorImpl<llvm::StringRef> &features);
+
+bool isFeatureEnabled(const llvm::SmallVectorImpl<llvm::StringRef> &features,
+                      llvm::StringRef feature);

driver/tool.cpp

@@ -121,62 +121,45 @@ void appendTargetArgsForGcc(std::vector<std::string> &args) {
     }
     return;
 
-  case Triple::riscv64:
-    {
-      extern llvm::TargetMachine* gTargetMachine;
-      auto featuresStr = gTargetMachine->getTargetFeatureString();
-      llvm::SmallVector<llvm::StringRef, 8> features;
-      featuresStr.split(features, ",", -1, false);
-
-      std::string mabi = getABI(triple, features);
-      args.push_back("-mabi=" + mabi);
-
-      // Returns true if 'feature' is enabled and false otherwise. Handles the
-      // case where the feature is specified multiple times ('+m,-m'), and
-      // takes the last occurrence.
-      auto hasFeature = [&features](llvm::StringRef feature) {
-        for (int i = features.size() - 1; i >= 0; i--) {
-          auto f = features[i];
-          if (f.substr(1) == feature) {
-            return f[0] == '+';
-          }
-        }
-        return false;
-      };
-
-      std::string march;
-      if (triple.isArch64Bit())
-        march = "rv64";
-      else
-        march = "rv32";
-      bool m = hasFeature("m");
-      bool a = hasFeature("a");
-      bool f = hasFeature("f");
-      bool d = hasFeature("d");
-      bool c = hasFeature("c");
-      bool g = false;
-
-      if (m && a && f && d) {
-        march += "g";
-        g = true;
-      } else {
-        march += "i";
-        if (m)
-          march += "m";
-        if (a)
-          march += "a";
-        if (f)
-          march += "f";
-        if (d)
-          march += "d";
-      }
-      if (c)
-        march += "c";
-      if (!g)
-        march += "_zicsr_zifencei";
-      args.push_back("-march=" + march);
+  case Triple::riscv64: {
+    extern llvm::TargetMachine* gTargetMachine;
+    const auto featuresStr = gTargetMachine->getTargetFeatureString();
+    llvm::SmallVector<llvm::StringRef, 8> features;
+    featuresStr.split(features, ",", -1, false);
+
+    const std::string mabi = getABI(triple, features);
+    args.push_back("-mabi=" + mabi);
+
+    std::string march = triple.isArch64Bit() ? "rv64" : "rv32";
+    const bool m = isFeatureEnabled(features, "m");
+    const bool a = isFeatureEnabled(features, "a");
+    const bool f = isFeatureEnabled(features, "f");
+    const bool d = isFeatureEnabled(features, "d");
+    const bool c = isFeatureEnabled(features, "c");
+    bool g = false;
+
+    if (m && a && f && d) {
+      march += "g";
+      g = true;
+    } else {
+      march += "i";
+      if (m)
+        march += "m";
+      if (a)
+        march += "a";
+      if (f)
+        march += "f";
+      if (d)
+        march += "d";
     }
+    if (c)
+      march += "c";
+    if (!g)
+      march += "_zicsr_zifencei";
+    args.push_back("-march=" + march);
     return;
+  }
+
   default:
     break;
   }