[llvm] [TableGen][RISCV] Add initial support for marking profiles as experimental (PR #91993)

[Alex Bradbury via llvm-commits]

https://github.com/asb created https://github.com/llvm/llvm-project/pull/91993

This is just the TableGen-side changes, split out as the minimal testable unit. It doesn't yet transition RVA23 and friends to be experimental (and add the necessary other changes for this to work).

Although choosing not to emit the SupportedExperimentalProfiles array if no experimental profiles are present isn't consistent with what we do for experimental extensions, we need to do this in order to avoid adding a warning for the empty array when building LLVM for as long as we don't have any experimental profiles defined.

>From 209a074c64843382b94a2491d0211309cfaed98c Mon Sep 17 00:00:00 2001
From: Alex Bradbury <asb at igalia.com>
Date: Mon, 13 May 2024 17:47:00 +0100
Subject: [PATCH] [TableGen][RISCV] Add initial support for marking profiles as
 experimental

This is just the TableGen-side changes, split out as the minimal
testable unit it doesn't yet transition RVA23 and friends to be
experimental (and add the necessary other changes for this to work).

Although choosing not to emit the SupportedExperimentalProfiles array if
no experimental profiles are present isn't consistent with what we do
for experimental extensions, we need to do this in order to avoid adding
a warning for the empty array when building LLVM for as long as we don't
have any experimental profiles defined.
---
 llvm/lib/Target/RISCV/RISCVProfiles.td        | 11 +++++-
 llvm/test/TableGen/riscv-target-def.td        | 13 ++++++-
 llvm/utils/TableGen/RISCVTargetDefEmitter.cpp | 35 ++++++++++++++-----
 3 files changed, 48 insertions(+), 11 deletions(-)

diff --git a/llvm/lib/Target/RISCV/RISCVProfiles.td b/llvm/lib/Target/RISCV/RISCVProfiles.td
index 5c13710faf65b..031f0a3881f75 100644
--- a/llvm/lib/Target/RISCV/RISCVProfiles.td
+++ b/llvm/lib/Target/RISCV/RISCVProfiles.td
@@ -8,7 +8,16 @@
 
 class RISCVProfile<string name, list<SubtargetFeature> features>
     : SubtargetFeature<name, "Is" # NAME, "true",
-                       "RISC-V " # name # " profile", features>;
+                       "RISC-V " # name # " profile", features> {
+  // Indicates if the profile is not yet ratified, so should be treated as
+  // experimental.
+  bit Experimental = false;
+}
+
+class RISCVExperimentalProfile<string name, list<SubtargetFeature> features>
+    : RISCVProfile<"experimental-"#name, features> {
+  let Experimental = true;
+}
 
 defvar RVI20U32Features = [Feature32Bit, FeatureStdExtI];
 defvar RVI20U64Features = [Feature64Bit, FeatureStdExtI];
diff --git a/llvm/test/TableGen/riscv-target-def.td b/llvm/test/TableGen/riscv-target-def.td
index 7f3d9bdb278ca..e328a6e3b5834 100644
--- a/llvm/test/TableGen/riscv-target-def.td
+++ b/llvm/test/TableGen/riscv-target-def.td
@@ -53,12 +53,19 @@ def FeatureDummy
 
 class RISCVProfile<string name, list<SubtargetFeature> features>
     : SubtargetFeature<name, "Is" # NAME, "true",
-                       "RISC-V " # name # " profile", features>;
+                       "RISC-V " # name # " profile", features> {
+  bit Experimental = false;
+}
+class RISCVExperimentalProfile<string name, list<SubtargetFeature> features>
+    : RISCVProfile<"experimental-"#name, features> {
+  let Experimental = true;
+}
 
 def RVI20U32 : RISCVProfile<"rvi20u32", [Feature32Bit, FeatureStdExtI]>;
 def RVI20U64 : RISCVProfile<"rvi20u64", [Feature64Bit, FeatureStdExtI]>;
 def ProfileDummy : RISCVProfile<"dummy", [Feature64Bit, FeatureStdExtI,
                                           FeatureStdExtF, FeatureStdExtZidummy]>;
+def RVI99U64 : RISCVExperimentalProfile<"rvi99u64", [Feature64Bit, FeatureStdExtI]>;
 
 class RISCVProcessorModel<string n,
                           SchedMachineModel m,
@@ -139,6 +146,10 @@ def ROCKET : RISCVTuneProcessorModel<"rocket",
 // CHECK-NEXT:     {"rvi20u64","rv64i2p1"},
 // CHECK-NEXT: };
 
+// CHECK:      static constexpr RISCVProfile SupportedExperimentalProfiles[] = {
+// CHECK-NEXT:     {"experimental-rvi99u64","rv64i2p1"},
+// CHECK-NEXT: };
+
 // CHECK:      #endif // GET_SUPPORTED_PROFILES
 
 // CHECK:      #ifndef PROC
diff --git a/llvm/utils/TableGen/RISCVTargetDefEmitter.cpp b/llvm/utils/TableGen/RISCVTargetDefEmitter.cpp
index bb409ea6ea692..d174b1961344f 100644
--- a/llvm/utils/TableGen/RISCVTargetDefEmitter.cpp
+++ b/llvm/utils/TableGen/RISCVTargetDefEmitter.cpp
@@ -122,6 +122,26 @@ static void printMArch(raw_ostream &OS, const std::vector<Record *> &Features) {
     OS << LS << Ext.first << Ext.second.Major << 'p' << Ext.second.Minor;
 }
 
+static void printProfileTable(raw_ostream &OS,
+                              const std::vector<Record *> &Profiles,
+                              bool Experimental) {
+  OS << "static constexpr RISCVProfile Supported";
+  if (Experimental)
+    OS << "Experimental";
+  OS << "Profiles[] = {\n";
+
+  for (const Record *Rec : Profiles) {
+    if (Rec->getValueAsBit("Experimental") != Experimental)
+      continue;
+
+    OS.indent(4) << "{\"" << Rec->getValueAsString("Name") << "\",\"";
+    printMArch(OS, Rec->getValueAsListOfDefs("Implies"));
+    OS << "\"},\n";
+  }
+
+  OS << "};\n\n";
+}
+
 static void emitRISCVProfiles(RecordKeeper &Records, raw_ostream &OS) {
   OS << "#ifdef GET_SUPPORTED_PROFILES\n";
   OS << "#undef GET_SUPPORTED_PROFILES\n\n";
@@ -129,15 +149,12 @@ static void emitRISCVProfiles(RecordKeeper &Records, raw_ostream &OS) {
   auto Profiles = Records.getAllDerivedDefinitionsIfDefined("RISCVProfile");
 
   if (!Profiles.empty()) {
-    llvm::sort(Profiles, LessRecordFieldName());
-    OS << "static constexpr RISCVProfile SupportedProfiles[] = {\n";
-    for (const Record *Rec : Profiles) {
-      OS.indent(4) << "{\"" << Rec->getValueAsString("Name") << "\",\"";
-      printMArch(OS, Rec->getValueAsListOfDefs("Implies"));
-      OS << "\"},\n";
-    }
-
-    OS << "};\n\n";
+    printProfileTable(OS, Profiles, /*Experimental=*/false);
+    bool HasExperimentalProfiles = any_of(Profiles, [&](auto &Rec) {
+      return Rec->getValueAsBit("Experimental");
+    });
+    if (HasExperimentalProfiles)
+      printProfileTable(OS, Profiles, /*Experimental=*/true);
   }
 
   OS << "#endif // GET_SUPPORTED_PROFILES\n\n";