[llvm] [RISCV] Introduce a new tune feature string syntax and its parser (PR #168160)

[Sam Elliott via llvm-commits]

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@@ -145,6 +149,101 @@ void getFeaturesForCPU(StringRef CPU,
       EnabledFeatures.push_back(F.substr(1));
 }
 
+using RISCVImpliedTuneFeature = std::pair<const char *, const char *>;
+
+#define GET_TUNE_FEATURES
+#define GET_IMPLIED_TUNE_FEATURES
+#include "llvm/TargetParser/RISCVTargetParserDef.inc"
+
+void getAllTuneFeatures(SmallVectorImpl<StringRef> &Features) {
+  Features.assign(std::begin(TuneFeatures), std::end(TuneFeatures));
+}
+
+Error parseTuneFeatureString(StringRef TFString,
+                             SmallVectorImpl<std::string> &ResFeatures) {
+  const StringSet<> AllTuneFeatureSet(llvm::from_range, TuneFeatures);
+  using SmallStringSet = SmallSet<StringRef, 4>;
+
+  TFString = TFString.trim();
+  // Note: StringSet is not really ergnomic to use in this case here.
+  SmallStringSet PositiveFeatures;
+  SmallStringSet NegativeFeatures;
+  // Phase 1: Collect explicit features.
+  StringRef FeatureStr;
+  do {
+    std::tie(FeatureStr, TFString) = TFString.split(",");
+    if (AllTuneFeatureSet.count(FeatureStr)) {
+      if (!PositiveFeatures.insert(FeatureStr).second)
+        return createStringError(inconvertibleErrorCode(),
+                                 "cannot specify more than one instance of '" +
+                                     Twine(FeatureStr) + "'");
+    } else if (FeatureStr.starts_with("no-")) {
+      // Check if this is a negative feature, like `no-foo` for `foo`.
+      StringRef ActualFeature = FeatureStr.drop_front(3);
+      if (AllTuneFeatureSet.count(ActualFeature)) {
+        if (!NegativeFeatures.insert(ActualFeature).second)
+          return createStringError(
+              inconvertibleErrorCode(),
+              "cannot specify more than one instance of '" + Twine(FeatureStr) +
+                  "'");
+      }
+    } else {
+      return createStringError(inconvertibleErrorCode(),
+                               "unrecognized tune feature directive '" +
+                                   Twine(FeatureStr) + "'");
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lenary wrote:

Agreed.

https://github.com/llvm/llvm-project/pull/168160