[RISCV] Introduce a new syntax for specifying tuning feature strings

mshockwave · lenary · mshockwave · commit ef9637b5e743 · 2025-11-14T15:27:16.000-08:00
Co-Authored-By: Sam Elliott &lt;aelliott@qti.qualcomm.com&gt;
diff --git a/llvm/include/llvm/TargetParser/RISCVTargetParser.h b/llvm/include/llvm/TargetParser/RISCVTargetParser.h
@@ -16,6 +16,7 @@
 
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Compiler.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -54,6 +55,9 @@ static constexpr unsigned RVVBytesPerBlock = RVVBitsPerBlock / 8;
 LLVM_ABI void getFeaturesForCPU(StringRef CPU,
                                 SmallVectorImpl<std::string> &EnabledFeatures,
                                 bool NeedPlus = false);
+LLVM_ABI void getAllTuneFeatures(SmallVectorImpl<StringRef> &TuneFeatures);
+LLVM_ABI Error parseTuneFeatureString(
+    StringRef TFString, SmallVectorImpl<std::string> &TuneFeatures);
 LLVM_ABI bool parseCPU(StringRef CPU, bool IsRV64);
 LLVM_ABI bool parseTuneCPU(StringRef CPU, bool IsRV64);
 LLVM_ABI StringRef getMArchFromMcpu(StringRef CPU);
diff --git a/llvm/lib/Target/RISCV/RISCVFeatures.td b/llvm/lib/Target/RISCV/RISCVFeatures.td
@@ -1740,6 +1740,10 @@ def HasVendorXSMTVDot
 // LLVM specific features and extensions
 //===----------------------------------------------------------------------===//
 
+class RISCVTuneFeature<string name, string field_name, string value,
+                       string description, list<SubtargetFeature> implied = []>
+    : SubtargetFeature<name, field_name, value, description, implied>;
+
 // Feature32Bit exists to mark CPUs that support RV32 to distinguish them from
 // tuning CPU names.
 def Feature32Bit
@@ -1788,46 +1792,46 @@ def FeatureUnalignedVectorMem
                       "loads and stores">;
 
 def TuneNLogNVRGather
-   : SubtargetFeature<"log-vrgather", "RISCVVRGatherCostModel", "NLog2N",
+   : RISCVTuneFeature<"log-vrgather", "RISCVVRGatherCostModel", "NLog2N",
                       "Has vrgather.vv with LMUL*log2(LMUL) latency">;
 
-def TunePostRAScheduler : SubtargetFeature<"use-postra-scheduler",
+def TunePostRAScheduler : RISCVTuneFeature<"use-postra-scheduler",
     "UsePostRAScheduler", "true", "Schedule again after register allocation">;
 
-def TuneDisableMISchedLoadClustering : SubtargetFeature<"disable-misched-load-clustering",
+def TuneDisableMISchedLoadClustering : RISCVTuneFeature<"disable-misched-load-clustering",
     "EnableMISchedLoadClustering", "false", "Disable load clustering in the machine scheduler">;
 
-def TuneDisableMISchedStoreClustering : SubtargetFeature<"disable-misched-store-clustering",
+def TuneDisableMISchedStoreClustering : RISCVTuneFeature<"disable-misched-store-clustering",
     "EnableMISchedStoreClustering", "false", "Disable store clustering in the machine scheduler">;
 
-def TuneDisablePostMISchedLoadClustering : SubtargetFeature<"disable-postmisched-load-clustering",
+def TuneDisablePostMISchedLoadClustering : RISCVTuneFeature<"disable-postmisched-load-clustering",
     "EnablePostMISchedLoadClustering", "false", "Disable PostRA load clustering in the machine scheduler">;
 
-def TuneDisablePostMISchedStoreClustering : SubtargetFeature<"disable-postmisched-store-clustering",
+def TuneDisablePostMISchedStoreClustering : RISCVTuneFeature<"disable-postmisched-store-clustering",
     "EnablePostMISchedStoreClustering", "false", "Disable PostRA store clustering in the machine scheduler">;
 
 def TuneDisableLatencySchedHeuristic
-    : SubtargetFeature<"disable-latency-sched-heuristic", "DisableLatencySchedHeuristic", "true",
+    : RISCVTuneFeature<"disable-latency-sched-heuristic", "DisableLatencySchedHeuristic", "true",
                        "Disable latency scheduling heuristic">;
 
 def TunePredictableSelectIsExpensive
-    : SubtargetFeature<"predictable-select-expensive", "PredictableSelectIsExpensive", "true",
+    : RISCVTuneFeature<"predictable-select-expensive", "PredictableSelectIsExpensive", "true",
                        "Prefer likely predicted branches over selects">;
 
 def TuneOptimizedZeroStrideLoad
-   : SubtargetFeature<"optimized-zero-stride-load", "HasOptimizedZeroStrideLoad",
+   : RISCVTuneFeature<"optimized-zero-stride-load", "HasOptimizedZeroStrideLoad",
                       "true", "Optimized (perform fewer memory operations)"
                       "zero-stride vector load">;
 
 foreach nf = {2-8} in
   def TuneOptimizedNF#nf#SegmentLoadStore :
-      SubtargetFeature<"optimized-nf"#nf#"-segment-load-store",
+      RISCVTuneFeature<"optimized-nf"#nf#"-segment-load-store",
                        "HasOptimizedNF"#nf#"SegmentLoadStore",
                        "true", "vlseg"#nf#"eN.v and vsseg"#nf#"eN.v are "
                        "implemented as a wide memory op and shuffle">;
 
 def TuneVLDependentLatency
-    : SubtargetFeature<"vl-dependent-latency", "HasVLDependentLatency", "true",
+    : RISCVTuneFeature<"vl-dependent-latency", "HasVLDependentLatency", "true",
                        "Latency of vector instructions is dependent on the "
                        "dynamic value of vl">;
 
@@ -1839,50 +1843,50 @@ def Experimental
 // and instead split over multiple cycles. DLEN refers to the datapath width
 // that can be done in parallel.
 def TuneDLenFactor2
-   : SubtargetFeature<"dlen-factor-2", "DLenFactor2", "true",
+   : RISCVTuneFeature<"dlen-factor-2", "DLenFactor2", "true",
                       "Vector unit DLEN(data path width) is half of VLEN">;
 
 def TuneNoDefaultUnroll
-    : SubtargetFeature<"no-default-unroll", "EnableDefaultUnroll", "false",
+    : RISCVTuneFeature<"no-default-unroll", "EnableDefaultUnroll", "false",
                        "Disable default unroll preference.">;
 
 // SiFive 7 is able to fuse integer ALU operations with a preceding branch
 // instruction.
 def TuneShortForwardBranchOpt
-    : SubtargetFeature<"short-forward-branch-opt", "HasShortForwardBranchOpt",
+    : RISCVTuneFeature<"short-forward-branch-opt", "HasShortForwardBranchOpt",
                        "true", "Enable short forward branch optimization">;
 def HasShortForwardBranchOpt : Predicate<"Subtarget->hasShortForwardBranchOpt()">;
 def NoShortForwardBranchOpt : Predicate<"!Subtarget->hasShortForwardBranchOpt()">;
 
 def TuneShortForwardBranchIMinMax
-    : SubtargetFeature<"short-forward-branch-i-minmax", "HasShortForwardBranchIMinMax",
+    : RISCVTuneFeature<"short-forward-branch-i-minmax", "HasShortForwardBranchIMinMax",
                        "true", "Enable short forward branch optimization for min,max instructions in Zbb",
                        [TuneShortForwardBranchOpt]>;
 
 def TuneShortForwardBranchIMul
-    : SubtargetFeature<"short-forward-branch-i-mul", "HasShortForwardBranchIMul",
+    : RISCVTuneFeature<"short-forward-branch-i-mul", "HasShortForwardBranchIMul",
                        "true", "Enable short forward branch optimization for mul instruction",
                        [TuneShortForwardBranchOpt]>;
 
 // Some subtargets require a S2V transfer buffer to move scalars into vectors.
 // FIXME: Forming .vx/.vf/.wx/.wf can reduce register pressure.
 def TuneNoSinkSplatOperands
-    : SubtargetFeature<"no-sink-splat-operands", "SinkSplatOperands",
+    : RISCVTuneFeature<"no-sink-splat-operands", "SinkSplatOperands",
                        "false", "Disable sink splat operands to enable .vx, .vf,"
                        ".wx, and .wf instructions">;
 
 def TunePreferWInst
-    : SubtargetFeature<"prefer-w-inst", "PreferWInst", "true",
+    : RISCVTuneFeature<"prefer-w-inst", "PreferWInst", "true",
                        "Prefer instructions with W suffix">;
 
 def TuneConditionalCompressedMoveFusion
-    : SubtargetFeature<"conditional-cmv-fusion", "HasConditionalCompressedMoveFusion",
+    : RISCVTuneFeature<"conditional-cmv-fusion", "HasConditionalCompressedMoveFusion",
                        "true", "Enable branch+c.mv fusion">;
 def HasConditionalMoveFusion : Predicate<"Subtarget->hasConditionalMoveFusion()">;
 def NoConditionalMoveFusion  : Predicate<"!Subtarget->hasConditionalMoveFusion()">;
 
 def TuneHasSingleElementVecFP64
-    : SubtargetFeature<"single-element-vec-fp64", "HasSingleElementVectorFP64", "true",
+    : RISCVTuneFeature<"single-element-vec-fp64", "HasSingleElementVectorFP64", "true",
                        "Certain vector FP64 operations produce a single result "
                        "element per cycle">;
 
@@ -1899,11 +1903,11 @@ def TuneVentanaVeyron : SubtargetFeature<"ventana-veyron", "RISCVProcFamily", "V
 def TuneAndes45 : SubtargetFeature<"andes45", "RISCVProcFamily", "Andes45",
                                    "Andes 45-Series processors">;
 
-def TuneVXRMPipelineFlush : SubtargetFeature<"vxrm-pipeline-flush", "HasVXRMPipelineFlush",
+def TuneVXRMPipelineFlush : RISCVTuneFeature<"vxrm-pipeline-flush", "HasVXRMPipelineFlush",
                                              "true", "VXRM writes causes pipeline flush">;
 
 def TunePreferVsetvliOverReadVLENB
-    : SubtargetFeature<"prefer-vsetvli-over-read-vlenb",
+    : RISCVTuneFeature<"prefer-vsetvli-over-read-vlenb",
                        "PreferVsetvliOverReadVLENB",
                        "true",
                        "Prefer vsetvli over read vlenb CSR to calculate VLEN">;
diff --git a/llvm/lib/TargetParser/RISCVTargetParser.cpp b/llvm/lib/TargetParser/RISCVTargetParser.cpp
@@ -12,7 +12,11 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/TargetParser/RISCVTargetParser.h"
+#include "llvm/ADT/SetOperations.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/StringSet.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/TargetParser/RISCVISAInfo.h"
 
@@ -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) + "'");
+    }
+  } while (!TFString.empty());
+
+  auto Intersection =
+      llvm::set_intersection(PositiveFeatures, NegativeFeatures);
+  if (!Intersection.empty()) {
+    std::string IntersectedStr = join(Intersection, "', '");
+    return createStringError(inconvertibleErrorCode(),
+                             "Feature(s) '" + Twine(IntersectedStr) +
+                                 "' cannot appear in both "
+                                 "positive and negative directives");
+  }
+
+  // Phase 2: Derive implied features.
+  StringMap<SmallVector<StringRef, 2>> ImpliedFeatureMap;
+  StringMap<SmallVector<StringRef, 2>> InverseImpliedFeatureMap;
+  for (auto [Feature, ImpliedFeature] : ImpliedTuneFeatures) {
+    ImpliedFeatureMap[Feature].push_back(ImpliedFeature);
+    InverseImpliedFeatureMap[ImpliedFeature].push_back(Feature);
+  }
+
+  for (StringRef PF : PositiveFeatures) {
+    auto ItFeatures = ImpliedFeatureMap.find(PF);
+    if (ItFeatures != ImpliedFeatureMap.end())
+      PositiveFeatures.insert(ItFeatures->second.begin(),
+                              ItFeatures->second.end());
+  }
+  for (StringRef NF : NegativeFeatures) {
+    auto ItFeatures = InverseImpliedFeatureMap.find(NF);
+    if (ItFeatures != InverseImpliedFeatureMap.end())
+      NegativeFeatures.insert(ItFeatures->second.begin(),
+                              ItFeatures->second.end());
+  }
+
+  Intersection = llvm::set_intersection(PositiveFeatures, NegativeFeatures);
+  if (!Intersection.empty()) {
+    std::string IntersectedStr = join(Intersection, "', '");
+    return createStringError(inconvertibleErrorCode(),
+                             "Feature(s) '" + Twine(IntersectedStr) +
+                                 "' were implied by both "
+                                 "positive and negative directives");
+  }
+
+  // Export the result.
+  const std::string PosPrefix("+");
+  const std::string NegPrefix("-");
+  for (StringRef PF : PositiveFeatures)
+    ResFeatures.emplace_back(PosPrefix + PF.str());
+  for (StringRef NF : NegativeFeatures)
+    ResFeatures.emplace_back(NegPrefix + NF.str());
+
+  return Error::success();
+}
 } // namespace RISCV
 
 namespace RISCVVType {
diff --git a/llvm/unittests/TargetParser/RISCVTargetParserTest.cpp b/llvm/unittests/TargetParser/RISCVTargetParserTest.cpp
@@ -7,6 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/TargetParser/RISCVTargetParser.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallVector.h"
 #include "gtest/gtest.h"
 
 using namespace llvm;
@@ -30,4 +32,90 @@ TEST(RISCVVType, CheckSameRatioLMUL) {
   EXPECT_EQ(RISCVVType::LMUL_F2,
             RISCVVType::getSameRatioLMUL(8, RISCVVType::LMUL_F4, 16));
 }
+
+TEST(RISCVTuneFeature, AllTuneFeatures) {
+  SmallVector<StringRef> AllTuneFeatures;
+  RISCV::getAllTuneFeatures(AllTuneFeatures);
+  EXPECT_EQ(AllTuneFeatures.size(), 28U);
+  for (auto F : {"conditional-cmv-fusion",
+                 "dlen-factor-2",
+                 "disable-latency-sched-heuristic",
+                 "disable-misched-load-clustering",
+                 "disable-misched-store-clustering",
+                 "disable-postmisched-load-clustering",
+                 "disable-postmisched-store-clustering",
+                 "single-element-vec-fp64",
+                 "log-vrgather",
+                 "no-default-unroll",
+                 "no-sink-splat-operands",
+                 "optimized-nf2-segment-load-store",
+                 "optimized-nf3-segment-load-store",
+                 "optimized-nf4-segment-load-store",
+                 "optimized-nf5-segment-load-store",
+                 "optimized-nf6-segment-load-store",
+                 "optimized-nf7-segment-load-store",
+                 "optimized-nf8-segment-load-store",
+                 "optimized-zero-stride-load",
+                 "use-postra-scheduler",
+                 "predictable-select-expensive",
+                 "prefer-vsetvli-over-read-vlenb",
+                 "prefer-w-inst",
+                 "short-forward-branch-i-minmax",
+                 "short-forward-branch-i-mul",
+                 "short-forward-branch-opt",
+                 "vl-dependent-latency",
+                 "vxrm-pipeline-flush"})
+    EXPECT_TRUE(is_contained(AllTuneFeatures, F));
+}
+
+TEST(RISCVTuneFeature, LegalTuneFeatureStrings) {
+  SmallVector<std::string> Result;
+  EXPECT_FALSE(errorToBool(RISCV::parseTuneFeatureString(
+      "log-vrgather,no-short-forward-branch-opt,vl-dependent-latency",
+      Result)));
+  EXPECT_TRUE(is_contained(Result, "+log-vrgather"));
+  EXPECT_TRUE(is_contained(Result, "+vl-dependent-latency"));
+  EXPECT_TRUE(is_contained(Result, "-short-forward-branch-opt"));
+  EXPECT_TRUE(is_contained(Result, "-short-forward-branch-i-minmax"));
+  EXPECT_TRUE(is_contained(Result, "-short-forward-branch-i-mul"));
+
+  Result.clear();
+  EXPECT_FALSE(errorToBool(RISCV::parseTuneFeatureString(
+      "no-short-forward-branch-i-mul,short-forward-branch-i-minmax", Result)));
+  EXPECT_TRUE(is_contained(Result, "+short-forward-branch-i-minmax"));
+  EXPECT_TRUE(is_contained(Result, "+short-forward-branch-opt"));
+  EXPECT_TRUE(is_contained(Result, "-short-forward-branch-i-mul"));
+
+  Result.clear();
+  EXPECT_FALSE(errorToBool(RISCV::parseTuneFeatureString(
+      "no-no-default-unroll,no-sink-splat-operands", Result)));
+  EXPECT_TRUE(is_contained(Result, "+no-sink-splat-operands"));
+  EXPECT_TRUE(is_contained(Result, "-no-default-unroll"));
+}
+
+TEST(RISCVTuneFeature, UnrecognizedTuneFeature) {
+  SmallVector<std::string> Result;
+  EXPECT_EQ(toString(RISCV::parseTuneFeatureString("32bit", Result)),
+            "unrecognized tune feature directive '32bit'");
+}
+
+TEST(RISCVTuneFeature, DuplicatedFeatures) {
+  SmallVector<std::string> Result;
+  EXPECT_EQ(toString(RISCV::parseTuneFeatureString("log-vrgather,log-vrgather",
+                                                   Result)),
+            "cannot specify more than one instance of 'log-vrgather'");
+
+  EXPECT_EQ(toString(RISCV::parseTuneFeatureString(
+                "log-vrgather,no-log-vrgather,short-forward-branch-i-mul,no-"
+                "short-forward-branch-i-mul",
+                Result)),
+            "Feature(s) 'log-vrgather', 'short-forward-branch-i-mul' cannot "
+            "appear in both positive and negative directives");
+
+  EXPECT_EQ(
+      toString(RISCV::parseTuneFeatureString(
+          "short-forward-branch-i-mul,no-short-forward-branch-opt", Result)),
+      "Feature(s) 'short-forward-branch-i-mul', 'short-forward-branch-opt' "
+      "were implied by both positive and negative directives");
+}
 } // namespace
diff --git a/llvm/utils/TableGen/Basic/RISCVTargetDefEmitter.cpp b/llvm/utils/TableGen/Basic/RISCVTargetDefEmitter.cpp
